Associations between urinary phthalate metabolites and bisphenol A levels, and serum thyroid hormones among the Korean adult population - Korean National Environmental Health Survey (KoNEHS) 2012-2014

Association between multipollutant exposure and thyroid hormones in elderly people: A cross-sectional study in China

Environmental chemicals have been indicated to cause disruption of thyroid homeostasis in human populations. However, previous studies mostly focused on single group of chemicals. Herein, we investigate the independent and combined effects of multiple pollutants on thyroid homeostasis, including thyroid-stimulating hormone (TSH), total and free thyroxine (tT4 and fT4) and total and free triiodothyronine (tT3 and fT3) in elderly people. These environmental pollutants (n = 144) are from ten categories, including phenols, parabens, perfluoroalkyl substances (PFASs), polychlorinated biphenyls (PCBs), phthalate esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), synthetic pyrethroids (SPs), herbicides, and metals. Few studies have evaluated the health risks of these 144 chemicals, especially their joint effects. In single-pollutant evaluations, multiple linear regression (MLR) models were used to estimate the independent associations between multiple exposures and thyroid biomarkers. In multi-pollutant evaluations, elastic net regression and Bayesian kernel machine regression (BKMR) models were used to estimate the combined associations. The MLR models showed that 41 chemicals were significantly related to THs levels. BKMR models revealed the most important chemical groups: metals for TSH, PAHs, SPs and PCBs for tT4, herbicides and SPs for tT3. This study will contribute to the understanding of multipollutant exposure and help prioritize specific chemical groups related to thyroid hormone disruption.

Connecting Bisphenol A Exposure to PCOS: Findings from a Case-Control Investigation

Polycystic Ovary Syndrome (PCOS) is a multifaceted condition influenced by genetic, hormonal, and environmental factors. Among environmental factors, Bisphenol A (BPA)-a recognized endocrine disruptor-has been implicated in the development of PCOS. The study aimed to compare BPA levels in women diagnosed with PCOS with those in healthy controls, using the high-performance liquid chromatography (HPLC) technique. The study involved 80 women diagnosed with PCOS and 50 healthy control participants. Demographic and biochemical parameters were recorded, including age, Body Mass Index (BMI), and levels of testosterone, estradiol, Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH), Prolactin (PRL), Dehydroepiandrosterone Sulfate (DHEA-S), Thyroid Stimulating Hormone (TSH), and Insulin Resistance as measured by the Homeostatic Model Assessment (HOMA-IR). Furthermore, BPA levels were measured using the HPLC technique. Women with PCOS exhibited significantly higher mean age and BMI compared to healthy controls (p = 0.01, p < 0.0001, respectively). Additionally, higher levels of testosterone (p = 0.04), LH (p = 0.03) and BPA (p < 0.0001) were observed in women with PCOS. However, estradiol, FSH, PRL, LH/FSH ratio, DHEA-S, and TSH levels were not significantly different between the two groups. HOMA-IR levels were not recorded for the control group. A notable positive relationship emerged between Bisphenol A and luteinizing hormone (LH) levels (r = 0.23, p = 0.03), also significant negative correlation appeared between Bisphenol A and thyroid-stimulating hormone (TSH) levels. This study found that women with PCOS have elevated BPA levels compared with healthy controls, showing a need for further research on the relationship between BPA exposure and the development of PCOS.

Sex-specific association of exposure to a mixture of phenols, parabens, and phthalates with thyroid hormone and antibody levels in US adolescents and adults

Individuals are exposed to multiple phenols, parabens, and phthalates simultaneously since they are important endocrine-disrupting compounds (EDCs) and share common exposure pathways. It is necessary to assess the effects of the co-exposure of these EDCs on thyroid hormones (THs). In this study, data included 704 adolescents and 2911 adults from the 2007-2012 National Health and Nutrition Examination Survey (NHANES). Serum THs measured total triiodothyronine (T3), total thyroxine (T4), free forms of T3 (FT3) and T4 (FT4), thyroid-stimulating hormone (TSH), thyroglobulin (Tg), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb). And 16 EDCs (3 phenols, 2 parabens, and 11 phthalates) were measured from urine. The relationship between single EDCs and single THs was analyzed using generalized linear regression. And results showed that several EDCs were positively associated with serum T3 and FT3 levels in boys but negatively associated with serum T4 and FT4 levels in girls. And in adults, five EDCs were negatively associated with T3, T4, or FT4. The effects of co-exposure to 16 EDCs on THs were calculated using Bayesian kernel machine regression and quantile-based g-computational modeling, confirmed that co-exposure was related to the increase of T3 in adolescents and the decrease of T4 in both adolescents and adults. Besides, nonlinear and linear relationships were identified between co-exposure and the risk of positive TPOAb and TgAb in girls and adult females, respectively. In conclusion, phenols, parabens, and phthalates as a mixture might interfere the concentrations of THs and thyroid autoantibodies, and the interfering effect varies significantly by sex as well as by age. Further prospective research is warranted to investigate the causal effects and underlying mechanisms of co-exposure on thyroid dysfunction.

Association of urinary bisphenols with thyroid function in the general population: a cross-sectional study of an industrial park in China

Bisphenols (BPs) are potential thyroid disruptors that are widely used in many consumer products, leading to their widespread exposure in the general population. Current cross-sectional and case-control studies have found associations between exposure to BPs and serum thyroid function, but the results were contradictory. The objectives of this study are to describe demographic characteristics, BP exposure levels, and thyroid function measurements in potentially exposed and control districts and to investigate the association of urinary BPs with thyroid function. Data were collected from a general population aged 3-79 years (N = 281) recruited by the Zhejiang Human Biomonitoring Program (ZJHBP). The concentrations of 10 kinds of BPs in urine and serum free triiodothyronine (FT3), total triiodothyronine (TT3), free thyroxine (FT4), total thyroxine (TT4), thyroid-stimulating hormone (TSH), thyroglobulin (Tg), thyroglobulin antibodies (TgAb), thyroid peroxidase antibodies (TPOAb), and thyrotropin receptor antibody (TRAb) in serum were measured. Multiple linear regression and weighted quantile sum (WQS) regression were used to estimate the relationship between single and mixed exposure of BPs and thyroid function. Bisphenol A (BPA), bisphenol S (BPS), and bisphenol P (BPP) were detected, respectively, in 82.73%, 94.24%, and 55.40% of the population in the exposed area and 81.69%, 61.27%, and 43.66% of the population in the control area. Among adult females, serum TT3 was negatively associated with urinary BPA (β = -0.033, 95% CI = -0.071, -0.008, P = 0.021). Among minor females, FT4 and Tg levels were negatively associated with the urinary BPA (β = -0.026, 95% CI = -0.051, -0.002, P = 0.032 for FT4; β = -0.129, 95% CI = -0.248, -0.009, P = 0.035 for Tg), and TPOAb was positively associated with urinary BPA (β = 0.104, 95% CI = 0.006, 0.203, P = 0.039). In WQS models, BPs mixture was positively associated with FT3 (βWQS = 0.022, 95% CI = 0.002, 0.042) and TT3 (βWQS = 0.033, 95% CI = 0.004, 0.062), and negatively associated with FT4 (βWQS = -0.024, 95% CI = -0.044, 0.004). We found widespread exposure to BPA, BPS, and BPP in the general population of Zhejiang province and found an association between BPA and thyroid hormones. This association is gender- and age-dependent and needs to be confirmed in further studies.

Are New Phthalate Ester Substitutes Safer than Traditional DBP and DiBP? Comparative Endocrine-Disrupting Analyses on Zebrafish Using In Vivo, Transcriptome, and In Silico Approaches

Although previous studies have confirmed the association between phthalate esters (PAEs) exposure and endocrine disorders in humans, few studies to date have systematically assessed the threats of new PAE alternatives to endocrine disruptions. Herein, zebrafish embryos were continuously exposed to two PAEs [di-n-butyl phthalate (DBP) and diisobutyl phthalate (DiBP)], two structurally related alternatives [diiononyl phthalate (DINP) and diisononyl hexahydrophthalate (DINCH)], and two non-PAE substitutes [dipropylene glycol dibenzoate (DGD) and glyceryl triacetate (GTA)], and the endocrine-disrupting effects were investigated during the early stages (8-48 hpf). For five endogenous hormones, including progesterone, testosterone, 17β-estradiol, triiodothyronine (T3), and cortisol, the tested chemicals disturbed the contents of at least one hormone at environmentally relevant concentrations (≤3.9 μM), except DINCH and GTA. Then, the concentration-dependent reduced zebrafish transcriptome analysis was performed. Thyroid hormone (TH)- and androgen/estrogen-regulated adverse outcome pathways (AOPs) were the two types of biological pathways most sensitive to PAE exposure. Notably, six compounds disrupted four TH-mediated AOPs, from the inhibition of deiodinases (molecular initiating event, MIE), a decrease in T3 levels (key event, KE), to mortality (adverse outcome, AO) with the quantitatively linear relationships between MIE-KE (|r| = 0.96, p = 0.002), KE-AO (|r| = 0.88, p = 0.02), and MIE-AO (|r| = 0.89, p = 0.02). Multiple structural analyses showed that benzoic acid is the critical toxicogenic fragment. Our data will facilitate the screening and development of green alternatives.

Sex-specific interactive effect of melamine and DEHP on a marker of early kidney damage in Taiwanese adults: A national population-based study from the Taiwan Biobank

Taiwan had the high incidence of chronic kidney disease (CKD) worldwide. Our objective was to examine associations between daily exposure of phthalates and melamine, two common nephrotoxins, and kidney damage risk in a well-established nationwide cohort. Study subjects were from Taiwan Biobank (TWB) with existing data of questionnaire and biochemical examinations. Average daily intake (ADI) levels of melamine and seven parental phthalates, including DEHP (di-2-ethylhexylphthalate), DiBP (Dibutyl phthalate), DnBP (Di-n-butyl phthalate), BBzP (Butyl benzyl phthalate), DEP (Diethyl phthalate), and DMP (Dimethyl phthalate) were estimated using a creatinine excretion-based model from urine melamine and 10 phthalate metabolites. Urine microalbumin to creatinine ratio (ACR) was used to represent for the outcome of kidney damage. Two statistical strategies were used: First, a weighted quantile sum (WQS) regression model to select the most important exposure variables of ADI levels of phthalates and melamine associated with ACR; Second, to examine effects of those most important exposure variables on ACR in multivariable linear regression models. In total, 1153 eligible adults were left for analyses. Of them, 591 (51.3%) and 562 (48.7%) were men and women, respectively, with a median age of 49 years old. By WQS, a significant and positive association was found between ADI of melamine and phthalates and ACR (β = 0.14, p = 0.002). ADI levels of melamine had the highest weight (0.57), followed by DEHP (0.13). Next, examining the two most important exposures in association with ACR, we found that the higher the melamine and DEHP intakes, the higher the ACR levels were found. An interaction effect was also found between melamine and DEHP intakes on urine ACR (p = 0.015). This result was more prominent in men (p = 0.008) than in women (p = 0.651). Environmental co-exposure of melamine and DEHP can potentially affect ACR in the community-dwelling Taiwanese adult population.

Endocrine-disrupting chemicals and autoimmune diseases

Endocrine-disrupting chemicals (EDCs) widely exist in people's production and life which have great potential to damage human and animal health. Over the past few decades, growing attention has been paid to the impact of EDCs on human health, as well as immune system. So far, researchers have proved that EDCs (such as bisphenol A (BPA), phthalate, tetrachlorodibenzodioxin (TCDD), etc.) affect human immune function and promotes the occurrence and development of autoimmune diseases (ADs). Therefore, in order to better understand how EDCs affect ADs, we summarized the current knowledge about the impact of EDCs on ADs, and elaborated the potential mechanism of the impact of EDCs on ADs in this review.

Re-evaluation of the risks to public health related to the presence of bisphenol A (BPA) in foodstuffs

In 2015, EFSA established a temporary tolerable daily intake (t-TDI) for BPA of 4 μg/kg body weight (bw) per day. In 2016, the European Commission mandated EFSA to re-evaluate the risks to public health from the presence of BPA in foodstuffs and to establish a tolerable daily intake (TDI). For this re-evaluation, a pre-established protocol was used that had undergone public consultation. The CEP Panel concluded that it is Unlikely to Very Unlikely that BPA presents a genotoxic hazard through a direct mechanism. Taking into consideration the evidence from animal data and support from human observational studies, the immune system was identified as most sensitive to BPA exposure. An effect on Th17 cells in mice was identified as the critical effect; these cells are pivotal in cellular immune mechanisms and involved in the development of inflammatory conditions, including autoimmunity and lung inflammation. A reference point (RP) of 8.2 ng/kg bw per day, expressed as human equivalent dose, was identified for the critical effect. Uncertainty analysis assessed a probability of 57-73% that the lowest estimated Benchmark Dose (BMD) for other health effects was below the RP based on Th17 cells. In view of this, the CEP Panel judged that an additional uncertainty factor (UF) of 2 was needed for establishing the TDI. Applying an overall UF of 50 to the RP, a TDI of 0.2 ng BPA/kg bw per day was established. Comparison of this TDI with the dietary exposure estimates from the 2015 EFSA opinion showed that both the mean and the 95th percentile dietary exposures in all age groups exceeded the TDI by two to three orders of magnitude. Even considering the uncertainty in the exposure assessment, the exceedance being so large, the CEP Panel concluded that there is a health concern from dietary BPA exposure.

Influence of mobile phase composition on the analytical sensitivity of LC-ESI-MS/MS for the concurrent analysis of bisphenols, parabens, chlorophenols, benzophenones, and alkylphenols

Phenols are significant environmental endocrine disruptors that can have adverse health effects on exposed individuals. Correlating phenol exposure to potential health implications requires the development of a comprehensive and sensitive analytical method capable of analyzing multiple phenols in a single sample preparation and analytical run. Currently, no such method is available for multiple classes of phenols due to electrospray ionization (ESI) limitations in concurrent ionization and lack of sensitivity to certain phenols, particularly alkylphenols. In this study, we investigated the influence of mobile phase compositions in ESI on concurrent ionization and analytical sensitivity of liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) during the analysis of multiple classes of phenols, and we propose a comprehensive and sensitive analytical method for various classes of phenols (i.e., bisphenols, parabens, benzophenones, chlorophenols, and alkylphenols). The proposed method was affected by 0.5 mM ammonium fluoride under methanol conditions. It enabled the concurrent ionization of all the phenols and significantly improved the analytical sensitivity for bisphenols and alkylphenols, which typically have poor ionization efficiency. This method, combined with a "dilute and shoot" approach, allowed us to simultaneously quantify 38 phenols with good chromatographic behavior and sensitivity. Furthermore, the method was successfully applied to the analysis of 61 urine samples collected from aquatic (swimming) and land (indoor volleyball and outdoor football) athletes.

Human exposure to a mixture of endocrine disruptors and serum levels of thyroid hormones: A cross-sectional study

Exposure to endocrine disruptors (EDCs) could disrupt thyroid hormone homeostasis. However, human epidemiological studies reported inconsistent observations, and scarce information on the effect of a mixture of chemicals. The aim of the present study was to examine the associations of multiple chemicals with thyroid hormones among adults from China. We measured serum levels of thyroid hormones and urinary levels of 11 EDCs, including six phthalate metabolites, bisphenol A (BPA), bisphenol F (BPF), bisphenol S (BPS), perchlorate, and thiocyanate among 177 healthy adults without occupational exposure. Associations of multiple urinary analytes with serum thyroid hormones were examined by performing general linear regression analysis and bayesian kernal machine regression analysis. These EDCs were detected in almost all samples. After adjusting for various covariates, we observed only BPF significantly associated with total thyroxin (TT4) (β=-0.27, 95% confidence interval (CI) [-0.41, -0.14]), total triiodothyronine (TT3) (β=-0.02 95% CI [-0.03, -0.01]), free T4 (fT4) (β=-0.02, 95% CI [-0.03, -0.01]), and free T3 (fT3) (β=-0.04, 95% CI [-0.07, -0.01]), and mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) and monoethyl phthalate (MEP) positively associated with TT4 (β=0.24, 95% CI [0.01, 0.48]) and fT4 (β=0.02, 95% CI [0.01, 0.04]), respectively. Moreover, we observed significant dose-response relationships between TT4 and the mixture of 11 EDCs, and BPF was the main contributor to the mixture effect, suggesting the priority of potential effect of BPF on disrupting thyroid function under a real scenario of human exposure to multiple EDCs. Our findings supported the hypothesis that human exposure to low levels of EDCs could alter thyroid hormones homeostasis among non-occupational healthy adults.

Association between bisphenol A exposure and thyroid dysfunction in adults: a systematic review and meta-analysis

The occurrence of thyroid dysfunction is affected by environmental factors, and BPA is a ubiquitous environmental pollutant with the potential to cause thyroid dysfunction. However, the limited epidemiological evidence shows an inconsistent association between BPA exposure and thyroid dysfunction. Therefore, the literature on the impact of BPA on thyroid was sorted and analyzed to study the relationship between BPA and adult thyroid function. The studies published on or before 23rd May 2022 from PubMed, Web of Science, and Scopus were collected analyzing the association between BPA exposure and the levels of thyroid hormones. The methodological quality of each study was assessed, the sensitivity analysis and subgroup analysis based on study population and gender were also performed, and publication bias was evaluated. A total of 2969 literature studies were retrieved. Based on inclusion and exclusion criteria, eleven studies were included. Our results showed that BPA concentration was negatively correlated with FT4 and TSH in males. Pooled correlation coefficients between BPA and FT4/TSH were -0.027 (95%CI = -0.030∼-0.024) and -0.058 (95%CI = -0.111∼-0.004). BPA concentration was positively correlated with FT4 in females, and the pooled correlation coefficient was 0.006 (95%CI = 0.003-0.008). The effects of BPA on thyroid hormone levels were significantly different between males and females. BPA may significantly decrease the levels of FT4 and TSH in males but increase the levels of FT4 in females. Considering the high heterogeneity among studies and the limited investigations into subgroups, the relationship between BPA exposure and thyroid dysfunction needs to be further investigated.

Assessing human exposure to phthalate esters in drinking water migrated from various pipe materials and water filter elements during water treatments and storage

Plastic water-supply pipes and filter element are frequently used in municipal water supply systems. Leaching of phthalate esters (PAEs) from these pipes and filter elements to drinking water has become a common concern among the public. In this study, the migrations of 16 phthalate esters (PAEs) in seven different kinds of water-supply product materials were investigated. Di-n-butyl phthalate (DBP) had the highest detection frequency of 54.4% in the water leaching samples of various water supply pipes and water filter elements samples, followed by Diisobutyl phthalate (DIBP, 46/90, 51.1%). The maximum detected concentration level for di(2-ethylhexyl) phthalate (DEHP), diethyl phthalate (DEP), and DBP in the leaching experiment was below the regulatory limit values of 8 µg/L, 300 µg/L, and 3 µg/L for each compound in China standards for drinking water quality. The increasing of the water temperature, the lower pH of the water, and the increasing of the leaching time will increase the migration of PAEs from plastic pipes into water. The chronic daily intake of children aged < 1-12 years to PAEs through drinking water was higher than the rest of the population groups. Carcinogenic risks (CR) of DEHP via drinking water were neglectable for most groups of people, while for young children with age of 1-2 years old, the CR is an acceptable risk.

Endocrine disrupting chemicals: effects on pituitary, thyroid and adrenal glands

BACKGROUND

In recent years, scientific research has increasingly focused on Endocrine Disrupting Chemicals (EDCs) and demonstrated their relevant role in the functional impairment of endocrine glands. This induced regulatory authorities to ban some of these compounds and to carefully investigate others in order to prevent EDCs-related conditions. As a result, we witnessed a growing awareness and interest on this topic.

AIMS

This paper aims to summarize current evidence regarding the detrimental effects of EDCs on pivotal endocrine glands like pituitary, thyroid and adrenal ones. Particularly, we directed our attention on the known and the hypothesized mechanisms of endocrine dysfunction brought by EDCs. We also gave a glimpse on recent findings from pioneering studies that could in the future shed a light on the pathophysiology of well-known, but poorly understood, endocrine diseases like hormone-producing adenomas.

CONCLUSIONS

Although intriguing, studies on endocrine dysfunctions brought by EDCs are challenging, in particular when investigating long-term effects of EDCs on humans. However, undoubtedly, it represents a new intriguing field of science research.

Di(2-ethylhexyl) phthalate induced thyroid toxicity via endoplasmic reticulum stress: In vivo and in vitro study

Di(2-ethylhexyl) phthalate (DEHP) could induce thyroid injury but the mechanism was unclear. This study combined in vivo and in vitro experiments to clarify the mechanism. In vivo, the offspring of Sprague Dawley rats were gavaged with different doses of DEHP (5, 50, and 250 mg/[kg⋅d]) from in utero to 12 weeks-old. Transcriptome sequencing was used to detect the mRNA expression profile of the offspring's thyroids. Differentially expressed genes were identified, followed by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. In vitro, Nthy-ori 3-1 cells were exposed to DEHP's metabolite mono (2-ethylhexyl) phthalate (MEHP) to verify the pathway we found by KEGG analysis. The results indicated that DEHP could disorder the thyroid hormones. Compared with the offspring in control group, the mRNA levels of 656 genes were upregulated in the offspring exposed to 50 mg/(kg⋅d) DEHP. The upregulated genes were enriched in the pathway of "protein processing in the endoplasmic reticulum (ER)." It indicated that the ER stress might play significant role in the thyroid toxicity induced by DEHP. In vitro, the mitochondrial membrane potential (ΔΨm) level of cells was decreased while the reactive oxygen species level was increased after MEHP exposure. MEHP increased the intracellular Ca²⁺ level and induced ER stress. After ER stress was inhibited by the 4-phenylbutyric acid, the thyroid toxicity caused by MEHP was alleviated. Taken together, our results indicated that DEHP could induce thyroid toxicity by activating ER stress.

Role of estrogen receptors in thyroid toxicity induced by mono (2-ethylhexyl) phthalate via endoplasmic reticulum stress: An in vitro mechanistic investigation

Mono(2-ethylhexyl) phthalate (MEHP) can influence the expression of estrogen receptors (ERs) and induce thyroid injury. The expression of ERs can be related to thyroid disease and abnormal expression of ERs has been associated with activation of endoplasmic reticulum stress. This study aimed to clarify the role of ERs in MEHP-induced thyroid damage via endoplasmic reticulum stress. We exposed Nthy-ori 3-1 cells to different doses of MEHP. We found that after the exposure, the cell viability and the expression levels of thyroid hormone metabolism-related proteins decreased, while the apoptosis level and the expression levels of ERs (ERα and GPR30) increased. Three endoplasmic reticulum stress-related signaling pathways were activated by MEHP. After ERα and GPR30 were knocked down, these three pathways were inhibited and the thyroid toxicity was alleviated. Taken together, our results indicate that MEHP can induce thyroid toxicity by upregulating the expression of ERs, further activating endoplasmic reticulum stress.

The independent and interactive effects of phthalates exposure and hypertension on the indicators of early renal injury in US adults: Evidence from NHANES 2001-2004

The association between phthalates and early renal injury is largely unknown in adults. We aim to explore the associations of phthalates and hypertension with early renal injury, and the interactive effects of phthalate and hypertension on the early renal injury. This study enrolled 3283 U.S. adults from NHANES 2001-2004. We detected nine phthalate metabolites in spot urine. We also measured the multiple indicators of early renal injury, including albumin-to-creatinine (Cr) ratio (ACR), β2-microglobulin (B2M), cystatin C (CYST), and calculated the estimated glomerular filtration rate (eGFR), including Cr-based eGFR, CYST-based eGFR, and Cr-CYST-based eGFR. Multiple linear regression and multivariable logistic regression were used to explore the associations among urinary phthalate metabolites, hypertension, and the indicators of early renal injury. The results showed that monobenzyl phthalate (MBzP), mono (3-carboxypropyl) phthalate (MCPP), and mono (2-ethylhexyl) phthalate (MEHP) were positively associated with ACR, B2M, CYST and negatively associated with three eGFR. Mono(2-ethyl-5-oxohexyl) phthalate (MEOHP) was positively associated with ACR, with a β value of 0.099 (95% CI: 0.046, 0.152). Meanwhile, MEHP was associated with a higher risk of ACR abnormality, with an OR value of 1.258 (95% CI: 1.067, 1.482). MBzP, MCPP, and MEOHP increased the risks of ACR, B2M, CYST, and eGFR abnormality. Hypertension was positively associated with ACR, with a β value of 0.460 (95% CI: 0.360, 0.561). We also found interactive effects of monoethyl phthalate (MEP), MCPP, MBzP, monobutyl phthalate (MnBP), and hypertension on B2M, CYST, and three kinds of eGFR. Our results indicated that certain phthalate metabolites might contribute to increased risks of early renal injury. The hypertension population may be more sensitive to the early renal injury caused by phthalates exposure than the non-hypertension population.

Occurrence of Phthalate Acid Esters (PAEs) in Protected Agriculture Soils and Implications for Human Health Exposure

This study explored occurrence of phthalic acid esters (PAEs) in protected agriculture soils and assessed their potential health risks to humans. Results showed that DEHP and DBP were the most abundant PAEs congeners, with mean concentrations of 318.68 μg/kg and 137.56 μg/kg, respectively. DOP and BBP concentrations were relatively low, and DMP and DEP were not detected in all samples. DBP concentrations were higher than the allowable concentration standard value. Additionally, soil pH and organic matter were key environmental parameters which may play the vital roles to the occurrence of organic pollutants. Heath risk assessment results indicated that dermal contact was the predominant human exposure route under non-dietary conditions, and children obtained higher health risk scores than adults. In summary, the overall health risk scores were at an acceptable level. These results provide insights for assessing soil environmental safety and ecological risks in protected agricultural soil.

Mediation effects of thyroid function in the associations between phthalate exposure and lipid metabolism in adults

Phthalates are a group of industrial chemicals widely used in everyday products including cosmetics, food packaging and containers, plastics, and building materials. Previous studies have indicated that urinary phthalate metabolites are associated with metabolic effects including those on lipid metabolism, but the results are mixed. Furthermore, whether thyroid function mediates the association between phthalate exposure and lipid metabolism remains unclear. In the present study, we explored whether changes in thyroid function markers mediate the associations between phthalate exposure and lipid metabolism indicators in Taiwanese adults. The cross-sectional data were obtained from the Taiwan Environmental Survey for Toxicants conducted in 2013. Levels of 11 urinary phthalate metabolites, levels of 5 thyroid hormones, and 8 indicators of lipid metabolism were assessed in 222 Taiwanese adults. The relationships of urinary phthalate metabolite levels with serum thyroid hormone levels and lipid metabolism indicators were explored using multiple regression models. Mediation analysis was conducted to evaluate the role of thyroid function in the association between phthalate exposure and lipid metabolism. The metabolite of di(- 2-ethylhexyl) phthalate (∑DEHPm) exhibited a significant positive association with the lipid metabolite indicator of high-density lipoprotein cholesterol (HDL-C; β = 0.059, 95% confidence interval [CI] = 0.009, 0.109) in adults, and the thyroid function indicator thyroxine (T₄) had a significant negative association with the metabolite ∑DEHPm (β = - 0.059, 95% CI = - 0.101, - 0.016) and a significant negative association with HDL-C (β = - 0.284, 95% CI = - 0.440, - 0.128). The T₄ indirect effect was 0.015 (95% CI = - 0.0087, 0.05), and the mediation effect was 32.2%. Our results support the assumption that exposure to phthalates influences the homeostasis of lipid metabolism by interfering with thyroid function.

Gestational exposure to bisphenol A induces region-specific changes in brain metabolomic fingerprints in sheep

Fetal brain development depends on maternofetal thyroid function. In rodents and sheep, perinatal BPA exposure is associated with maternal and/or fetal thyroid disruption and alterations in central nervous system development as demonstrated by metabolic modulations in the encephala of mice. We hypothesized that a gestational exposure to a low dose of BPA affects maternofetal thyroid function and fetal brain development in a region-specific manner. Pregnant ewes, a relevant model for human thyroid and brain development, were exposed to BPA (5 µg/kg bw/d, sc). The thyroid status of ewes during gestation and term fetuses at delivery was monitored. Fetal brain development was assessed by metabolic fingerprints at birth in 10 areas followed by metabolic network-based analysis. BPA treatment was associated with a significant time-dependent decrease in maternal TT4 serum concentrations. For 8 fetal brain regions, statistical models allowed discriminating BPA-treated from control lambs. Metabolic network computational analysis revealed that prenatal exposure to BPA modulated several metabolic pathways, in particular excitatory and inhibitory amino-acid, cholinergic, energy and lipid homeostasis pathways. These pathways might contribute to BPA-related neurobehavioral and cognitive disorders. Discrimination was particularly clear for the dorsal hippocampus, the cerebellar vermis, the dorsal hypothalamus, the caudate nucleus and the lateral part of the frontal cortex. Compared with previous results in rodents, the use of a larger animal model allowed to examine specific brain areas, and generate evidence of the distinct region-specific effects of fetal BPA exposure on the brain metabolome. These modifications occur concomitantly to subtle maternal thyroid function alteration. The functional link between such moderate thyroid changes and fetal brain metabolomic fingerprints remains to be determined as well as the potential implication of other modes of action triggered by BPA such as estrogenic ones. Our results pave the ways for new scientific strategies aiming at linking environmental endocrine disruption and altered neurodevelopment.

Plasticizers: negative impacts on the thyroid hormone system

This review aims to understand the impacts of plasticizers on the thyroid system of animals and humans. The thyroid gland is one of the earliest endocrine glands that appear during embryogenesis. The thyroid gland synthesizes thyroid hormones (TH), triiodothyronine (T3), and thyroxine (T4) that are important in the regulation of body homeostasis. TH plays critical roles in regulating different physiological functions, including metabolism, cell growth, circadian rhythm, and nervous system development. Alteration in thyroid function can lead to different medical problems. In recent years, thyroid-related medical problems have increased and this could be due to rising environmental pollutants. Plasticizers are one such group of a pollutant that impacts thyroid function. Plasticizers are man-made chemicals used in a wide range of products, such as children's toys, food packaging items, building materials, medical devices, cosmetics, and ink. The increased use of plasticizers has resulted in their detection in the environment, animals, and humans. Studies indicated that plasticizers could alter thyroid function in both animals and humans at different levels. Several studies demonstrated a positive and/or negative correlation between plasticizers and serum T4 and T3 levels. Plasticizers could also change the expression of various TH-related genes and proteins, including thyroid-stimulating hormone (TSH), thyrotropin-releasing hormone (TRH), and transporters. Histological analyses demonstrated thyroid follicular cell hypertrophy and hyperplasia in response to several plasticizers. In conclusion, plasticizers could disrupt TH homeostasis and the mechanisms of toxicity could be diverse.

Maternal exposure to bis(2-ethylhexyl) phthalate during the thyroid hormone-dependent stage induces persistent emotional and cognitive impairment in middle-aged offspring mice

Prenatal DEHP exposure can cause offspring neurodevelopmental toxicity, but the persistent effects of such exposure window are unclear. This study aimed to investigate the lasting neurobehavioral impact of DEHP on offspring following early exposure from GD9.5 (fetal neural tube closure) to GD16.5 (fetal thyroxin, TH, synthesis). Data showed maternal exposure to DEHP during the thyroid hormone-dependent stage induced a range of neurobehavioral phenotypic changes in adult and middle-aged mice, including anxiety, depression and cognitive impairment. Significant reductions in free TH, TH transporters, and TH metabolic enzyme deiodinase II (D2) were observed in the fetal brain, whereas D3 was elevated, indicating that TH signaling disruption was caused by in utero exposure. Gene expression analyses suggested the expression levels of the TH receptors Trα1, Trβ1 and their downstream target, brain-derived neurotrophic factor, were significantly attenuated, which may partially explain the mechanisms of neurodevelopmental impairment. This study provides new evidence of the persistent effects of sex-specific neurodevelopmental impairment due to in utero DEHP exposure, possibly through damage to the fetal brain TH signaling systems that causes lifelong brain damage. These results further suggest a profound neurobehavioral toxicity of DEHP that may be programmed during early developmental stage exposure and manifested later in life.

Risk of Nonalcoholic Fatty Liver Disease Is Associated with Urinary Phthalate Metabolites Levels in Adults with Subclinical Hypothyroidism: Korean National Environmental Health Survey (KoNEHS) 2012-2014

Nonalcoholic fatty liver disease (NAFLD) is a condition of excess accumulation of fats in the liver. Thyroid dysfunction is commonly observed in adult populations with NAFLD. In subjects with thyroid dysfunction, phthalates, which are chemical compounds widely used to increase the flexibility of various plastic products, may increase the risk of NAFLD prevalence. Therefore, our study aimed to evaluate the relationship between the levels of urinary phthalate metabolites and the risk of NAFLD stratified by the levels of thyroid-stimulating hormone (TSH). Data (n = 2308) were obtained from the Korean National Environmental Health Survey II (2012−2014). Using the hepatic steatosis index, participants were classified into non-NAFLD (<30) and NAFLD (>36) groups. Participants with euthyroidism were defined as 0.45−4.5 mIU/L for serum TSH and normal thyroxine (T4) levels (n = 2125). Subclinical hypothyroidism (SCH) was defined as a higher TSH level (4.5−10 mIU/L) with normal total T4 levels in the serum (n = 183). A multivariate analysis was performed to assess the association of the urinary phthalate concentration with the risk of NAFLD after stratification based on the thyroid hormone levels. The levels of phthalate metabolites in urine were not significantly associated with NAFLD in adults with euthyroidism. However, a significant increased risk of NAFLD in those with SCH was observed in the fourth quartile of mono (2-ethyl-5-hydroxyhexyl) phthalate (odds ratio (OR) 13.59, 95% confidence interval (CI) 12.13−86.44), mono (2-ethyl-5-oxohexyl) phthalate (OR 8.55, 95% CI 1.20−60.53), mono-(2-ethyl-5-carboxypentyl) phthalate (OR 9.06, 95% CI 1.78−45.96), and mono-benzyl phthalate (OR 6.05, 95% CI 1.62−22.54) compared to those of the lowest quartile after being adjusted with covariates. In conclusion, the levels of phthalate metabolites in urine are positively associated with NAFLD in adults with SCH. More experimental studies are needed to clarify the risk of NAFLD caused by phthalate exposure in cases with poor thyroid function.

The associations of urinary DEHP metabolite levels, serum thyroid hormones, and thyroid-related genes among the adolescent students from China: a cross-sectional study

Our study aimed to investigate the associations between DEHP exposure and serum thyroid hormone levels in 347 adolescents and young adults. We measured DEHP metabolites including mono(2-ethylhexyl) phthalate (MEHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-carboxypentyl) phthalate (MECPP), and mono(2-carboxymethyl)hexyl phthalate (MCMHP) in their urine. Total thyroxine (TT4), total triiodothyronine, free triiodothyronine, free thyroxine (FT4), thyroid-stimulating hormone and the mRNA levels of thyroid peroxidase (TPO), thyroglobulin (TG), sodium iodide symporter (NIS), thyroid transcription factor 1 (TTF-1), and paired box gene 8 (PAX-8) in serum were measured. The results of statistical analysis showed that urinary DEHP metabolites were generally negatively associated with TT4 levels in serum. In the males, the FT4 levels showed positive associations with urinary MEHP, MECPP, MCMHP, and ∑DEHP. The mRNA level of TG was significantly positively correlated with the levels of MECPP, MCMHP, and ∑DEHP, while the levels of TTF-1 and PAX-8 mRNA were significantly positively correlated with the levels of DEHP metabolites. Taken together, DEHP may affect the synthesis of TG by altering the normal transcription of TTF-1 and PAX-8, leading to decreased TT4 levels in Chinese adolescents.

Lead, mercury, and cadmium exposures are associated with obesity but not with diabetes mellitus: Korean National Environmental Health Survey (KoNEHS) 2015-2017

BACKGROUND

Associations of heavy metal exposures with obesity and obesity-related traits have been suggested, while those with nonalcoholic fatty liver disease (NAFLD) and diabetes mellitus (DM) are often inconsistent.

METHODS

This study included 3787 adults aged ≥19 years who participated in the Korean National Environmental Health Survey 2015-2017, and investigated the association of toxic heavy metals with metabolic diseases. Lead (Pb), mercury (Hg), and cadmium (Cd) were measured either in urine (uHg, uCd) or total blood (bPb, bHg). Body mass index (BMI) was calculated, and DM cases were identified through a self-answered medication history. Hepatic Steatosis Index (HSI) as a surrogating index of NAFLD, was calculated using hepatic enzyme measurements, including aspartate aminotransferase (AST) and alanine aminotransferase (ALT).

RESULTS

Adults in the highest quartile of bPb, bHg, and uHg showed significantly elevated odds of obesity (BMI ≥25 kg/m²), compared to the lowest quartile (OR 1.58 for bPb, 1.92 for bHg, and 1.81 for uHg). HSI was positively correlated with bHg, uHg, and uCd concentrations. The odds of NAFLD (HSI ≥36) were also increased with increasing quartile of bHg, uHg, and uCd concentrations. For DM, bPb showed a significant negative association, while bHg and uCd exhibited non-monotonic and inconclusive associations.

CONCLUSIONS

Among the general adult population of Korea, both Pb and Hg exposures were associated with an increased risk of obesity. In addition, both Hg and Cd exposures were associated with increased odds of NAFLD. These metals, however, were not associated with an increased risk of DM.

Maternal Thyroid Anomalies and Attention-Deficit Hyperactivity Disorder in Progeny

Previous epidemiologic investigations suggested that maternal thyroid anomalies are a possible causal factor in attention-deficit hyperactivity disorder (ADHD) in progeny, yet clinical trials indicated that levothyroxine treatment was ineffective in preventing neurodevelopmental impairments. We used an Israeli cohort of 385,542 singleton births from 1999-2012 to explore the interrelated roles of maternal thyroid conditions, laboratory gestational thyroid hormone measurements, use of thyroid medications, and offspring ADHD. Analyses were performed using Cox proportional hazards models. Results indicated that maternal hypothyroidism diagnosis was associated with an elevated progeny ADHD hazard (adjusted hazard ratio = 1.14, 95% confidence interval = 1.10, 1.18). However, this association was unmitigated by gestational use of levothyroxine and was unexplained by maternal gestational thyroid hormone levels. Associations with gestational thyrotropin values and hypothyroxinemia were also observed but were robust only in mothers without other records indicative of a thyroid problem. Results indicated that maternal thyroid hypofunction was associated with progeny ADHD but possibly not due to a direct causal relationship. Instead, maternal thyroid hypofunction may serve as a proxy indicator for other factors that affect neurodevelopment through thyroid hormone independent pathways, which are thus unaffected by pharmaceutical treatments for thyroid hypofunction. Factors known to disrupt thyroid functioning should be examined for their independent ADHD-related effects.

Association of phthalates and early menarche in Korean adolescent girls from Korean National Environmental Health Survey (KoNEHS) 2015-2017

Background

Phthalates are one of renowned endocrine-disrupting chemicals, although inconsistent results are present around their effect on onset of menarche. Our hypothesis is that pre-pubertal exposure to phthalates is associated with acceleration of menarche.

Methods

We analyzed a total of 236 middle school (7th to 9th grade) girls from Korean National Environmental Health Survey 2015-2017. We used multiple linear regression to investigate impact of eight phthalate metabolites on age of menarche. We also conducted logistic regression to evaluate association between phthalate metabolite concentrations and early onset of menarche, adjusting for grade, maternal age of menarche and body mass index (BMI).

Results

In linear regression analysis, no significant association was found for any phthalate metabolites. In logistic regression analysis, however, odds ratios (ORs) of early menarche were significantly increased for mono-n-butyl phthalate (MnBP) and for sum of all phthalates. When compared to group with the lowest level, high concentration group for MnBP presented significantly increased odds of early menarche (OR: 2.09; 95% confidence interval [CI]: 1.03, 4.23) after adjusting for grade, maternal age of menarche and BMI. Furthermore, high concentrations of sum of all phthalates were associated with significant increase of OR of early menarche (OR: 2.22; 95% CI: 1.10, 4.49) after adjustment, compared to the lowest concentration group.

Conclusions

Results of our study suggest that exposure to phthalates around puberty may be associated with increased risk of early menarche.

Structural binding perspectives of common plasticizers and a flame retardant, BDE-153, against thyroxine-binding globulin: potential for endocrine disruption

The human exposure to diverse endocrine-disrupting chemicals (EDCs) has increased dramatically over several decades with very adverse health effects. Plasticizers and flame retardants constitute important classes of EDCs interfering in endocrine physiology including the thyroid function. Thyroxine (T4) is an important hormone regulating metabolism and playing key roles in developmental processes. In this study, six phthalate and nonphthalate plasticizers and one flame retardant (BDE-153) were subjected to structural binding against thyroxine-binding globulin (TBG). The aim was to understand their potential role in thyroid dysfunction using structural binding approach. The structural study was performed using Schrodinger's induced fit docking, followed by binding energy estimations of ligands and the molecular interaction analysis between the ligands and the amino acid residues in the TBG ligand-binding pocket. The results indicated that all the compounds packed tightly into the TBG ligand-binding pocket with similar binding pattern to that of TBG native ligand, T4. A high majority of TBG interacting amino acid residues for ligands showed commonality with native ligand, T4. The estimated binding energy values were highest for BDE-153 followed by nonphthalate plasticizer, DINCH, with values comparable with native ligand, T4. The estimated binding energy values of other plasticizers DEHP, DEHT, DEHA, ATBC, and TOTM were less than DINCH. In conclusion, the tight docking conformations, amino acid interactions, and binding energy values of the most of the indicated ligands were comparable with TBG native ligand, T4, suggesting their potential for thyroid dysfunction. The results revealed highest potential thyroid disruptive action for BDE-153 and DINCH.

Internal exposure of Chinese children from a typical coastal city to bisphenols and possible association with thyroid hormone levels

Bisphenols (BPs) are widely used in consumer products, and human exposure to BPs is nearly ubiquitous. However, human biomonitoring data are scarce, especially for children. In this study, we quantified eight BPs in the serum of 345 children from a typical coastal city in China. Bisphenol A (BPA), bisphenol F (BPF), and bisphenol S (BPS) were frequently detected (63% BPA, 68% BPF, 43% BPS), with geometric mean (GM) concentrations of 1.6, 0.08, and 0.04 ng/mL, respectively. The other five BPs had low detection frequencies (<5%). The distribution of BPA, BPF, and BPS in children's serum samples was independent of sex whereas the concentrations of BPS and BPF both significantly increased with age (P < 0.01). The GM values of estimated daily intake for BPA and BPS were 0.61 and 0.014 μg/kg body weight (bw)/day, respectively, indicating a relatively higher exposure risk of BPA in comparison with BPS. Compared with the population with euthyroid or nonhyperthyroid thyroid dysfunction, children with hyperthyroidism suffered higher exposure to BPA. By multiple linear regression analysis, thyroid-stimulating hormone showed a significantly negative relationship with log₁₀-BPA concentration for euthyroid children (R² = 0.477, P < 0.001), whereas a significantly positive correlation (R² = 0.753, P = 0.033) was found for hyperthyroid children.

Associations of serum phthalate metabolites with thyroid hormones in GraMo cohort, Southern Spain

The general population is continuously exposed to phthalates via various consumer products. Epidemiological research relating phthalate exposure to thyroid function during non-developmental periods is limited. This study aimed to investigate the associations between specific serum phthalate metabolites and indicators of thyroid function in adults. We measured 10 serum phthalate metabolites and thyroid hormones - total triiodothyronine (TT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) - in a subsample of 207 adults from the GraMo cohort. This subsample was made up of men and women (in equal proportions) of middle age (49 ± 17 years) and from Southern Spain (province of Granada). Data on age, sex, body mass index, residence area, tobacco use, alcohol consumption and attained education were obtained from a questionnaire. Phthalate metabolites were log-transformed and categorized into tertiles. Cross-sectional associations of each metabolite with thyroid hormones were analyzed using multivariable-adjusted linear regression models. The mixture effect of metabolite phthalates was assessed using weighted quantile sum regression. After multivariable-adjustment, the following phthalate metabolites were significantly associated with TT3 in a dose-response manner: MMP (β = 0.90: 95% confidence interval 0.68,1.12), MEP (β = 0.67: 0.44, 0.90), MiBP (β = 0.49: 0.21, 0.77), MiDP (β = 0.27: 0.03, 0.52), MBzP (β = 0.51: 0.28, 0.73), MEHP (β = -0.59: -0.82, -0.35) and MiNP (β = -0.43: -0.71, -0.14), when comparing highest vs. lowest exposed. The sum of all metabolites was also linked to FT4 levels. No significant associations were observed for TSH except for MiNP. Although phthalate metabolites with different molecular weight showed opposite associations, overall metabolite concentrations seem to associate with increased TT3 and FT4 serum levels. The cross-sectional nature of this analysis limits causal inference.

The effects of phthalate ester exposure on human health: A review

Phthalate esters (PAEs) are one of the most widely used plasticizers in polymer products and humans are increasingly exposed to them. The constant exposure to PAEs-contained products has raised some concerns against human health. Thus, the impacts of PAEs and their metabolites on human health require a comprehensive study for a better understanding of the associated risks. Here, we attempt to review eight main health effects of PAE exposure according to the most up-to-date studies. We found that epidemiological studies demonstrated a consistent association between PAE exposure (especially DEHP and its metabolites) and a decrease in sperm quality in males and symptom development of ADHD in children. Overall, we found insufficient evidence and lack of consistency of the association between PAE exposure and cardiovascular diseases (hypertension, atherosclerosis, and CHD), thyroid diseases, respiratory diseases, diabetes, obesity, kidney diseases, intelligence performance in children, and other reproductive system-related diseases (anogenital distance, girl precocious puberty, and endometriosis). Future studies (longitudinal and follow-up investigations) need to thoroughly perform in large-scale populations to yield more consistent and powerful results and increase the precision of the association as well as enhance the overall understanding of potential human health risks of PAEs in long-term exposure.

Endocrine disrupting chemicals and thyroid hormone action

Thyroid hormones (predominantly thyroxine, T4, and triiodothyronine, T3) are essential for normal development and for adult physiology. There are several challenges, however, that make identifying chemicals that produce adverse effects by interfering with the thyroid system difficult. First, individual variability in serum concentrations of thyroid hormones represent only about 10% of the population reference range that is considered to be "normal." This means that populations studies evaluating the relationship between chemical exposure and serum thyroid hormones must be large enough to overcome this internal variance. In addition, we know that there are chemicals that do not produce changes in thyroid hormone levels, but nevertheless impact thyroid signaling in target tissues. A good example is that of polychlorinated biphenyls (PCBs). PCB exposure during development are clearly associated with cognitive deficits in humans. But PCB exposure isn't uniformly associated with a reduction in serum thyroid hormone in human populations despite mechanistic studies showing that PCBs reduce serum T4 in animals. In contrast, perchlorate is a chemical that inhibits iodide uptake, thereby reducing thyroid hormone synthesis and serum hormone levels. Human studies have been variable in identifying a relationship between thyroid hormone and perchlorate exposure, but studies also show that dietary iodine, cigarette smoking and other factors can modify this relationship. The conclusion is that identifying chemicals that interfere with thyroid hormone could depend on in vitro analysis of chemicals that interact with different proteins important for thyroid hormone to function properly.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

Thyroid hormones are necessary for the normal functioning of physiological systems. Therefore, knowledge of any factor (whether genetic, environmental or intrinsic) that alters the levels of thyroid-stimulating hormone (TSH) and thyroid hormones is crucial. Genetic factors contribute up to 65% of interindividual variations in TSH and thyroid hormone levels, but many environmental factors can also affect thyroid function. This review discusses studies that have analyzed the impact of environmental factors on TSH and thyroid hormone levels in healthy adults. We included lifestyle factors (smoking, alcohol consumption, diet and exercise) and pollutants (chemicals and heavy metals). Many inconsistencies in the results have been observed between studies, making it difficult to draw a general conclusion about how a particular environmental factor influences TSH and thyroid hormone levels. However, lifestyle factors that showed the clearest association with TSH and thyroid hormones were smoking, body mass index (BMI) and iodine (micronutrient taken from the diet). Smoking mainly led to a decrease in TSH levels and an increase in triiodothyronine (T3) and thyroxine (T4) levels, while BMI levels were positively correlated with TSH and free T3 levels. Excess iodine led to an increase in TSH levels and a decrease in thyroid hormone levels. Among the pollutants analyzed, most studies observed a decrease in thyroid hormone levels after exposure to perchlorate. Future studies should continue to analyze the impact of environmental factors on thyroid function as they could contribute to understanding the complex background of gene-environment interactions underlying the pathology of thyroid diseases.

A critical review on human internal exposure of phthalate metabolites and the associated health risks

Phthalates (PAEs) are popular synthetic chemicals used as plasticizers and solvents for various products, such as polyvinyl chloride or personal care products. Human exposure to PAEs is associated with various diseases, resulting in PAE biomonitoring in humans. Inhalation, dietary ingestion, and dermal absorption are the major human exposure routes. However, estimating the actual exposure dose of PAEs via an external route is difficult. As a result, estimation by internal exposure has become the popular analytical methods to determine the concentrations of phthalate metabolites (mPAEs) in human matrices (such as urine, serum, breast milk, hair, and nails). The various exposure sources and patterns result in different composition profiles of PAEs in biomatrices, which vary from country to country. Nevertheless, the mPAEs of diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), di-iso-butyl phthalate (DiBP), and di-(2-ethylhexyl) phthalate (DEHP) are predominant in the urine. These mPAEs have greater potential health risks for humans. Children have been observed to exhibit higher exposure risks to several mPAEs than adults. Besides age, other influencing factors for phthalate exposure are gender, jobs, and residential areas. Although many studies have reported biological monitoring of PAEs, only a few reviews that adequately summarized the reports are available. The current review appraised available studies on mPAE quantitation in human biomatrices and estimated the dose and health risks of phthalate exposure. While some countries lack biomonitoring data, some countries' data do not reflect the current PAE exposure. Thence, future studies should involve frequent PAE biomonitoring to accurately estimate human exposure to PAEs, which will contribute to health risk assessments of human exposure to PAEs. Such would aid the formulation of corresponding regulations and restrictions by the government.

Mediation effects of thyroid function in the associations between phthalate exposure and glucose metabolism in adults

The mediating influence of thyroid function on the association of phthalate exposure with glucose metabolism, including insulin resistance, remains unclear. We explored the mediating influence of thyroid hormone levels on the phthalate exposure-insulin resistance association. This cross-sectional study of 217 Taiwanese adults assessed insulin resistance (Homeostatic Model Assessment for Insulin Resistance, HOMA-IR scores) and the levels of 11 urinary phthalate metabolites and 5 thyroid hormones. Multiple regression models were used to analyze the associations among serum thyroid hormone levels, urinary phthalate metabolite levels, and HOMA-IR scores. The mediation analysis assessed the influence of thyroid function on the phthalate exposure-HOMA-IR association. Our data indicated urinary mono-ethylhexyl phthalate (MEHP) levels was negatively associated with free thyroxine (T₄) (β = -0.018; 95% confidence interval [CI]: -0.031, -0.005) and positively associated with HOMA-IR scores (β = 0.051, 95% CI: 0.012, 0.090). The study also revealed urinary mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) levels was negatively associated with free T₄ (β = -0.036, 95% CI: -0.056, -0.017) and HOMA-IR (β = 0.070, 95% CI: 0.013, 0.126). Free T₄ and HOMA-IR had a negative association (β = -0.757, 95% CI: -1.122, -0.392). In the mediation analysis, free T₄ mediated 24% and 35% of the associations of urinary MEHP and MEOHP with HOMA-IR, respectively. Our findings revealed the mediating role of thyroid function in the phthalate exposure-glucose metabolism association in adults.

Human biomonitoring reference values and characteristics of Phthalate exposure in the general population of Taiwan: Taiwan Environmental Survey for Toxicants 2013-2016

Since a 2011 incident involving phthalate-tainted food, Taiwanese people have become concerned with food quality, and they are still being exposed to certain levels of phthalates. However, no nationwide human biomonitoring survey had been conducted to gather information on levels or reference values (RVs) of phthalates in the Taiwanese population. We aimed to establish the urinary levels and RVs of phthalate metabolites and identify exposure characteristics among Taiwan's population. We enrolled 1857 participants 7 years of age and older from the Taiwan Environmental Survey for Toxicants (TESTs) conducted during 2013-2016. Levels of 11 phthalate metabolites in each participant's urine samples were determined using liquid chromatography-tandem mass spectrometry. For all phthalate metabolites except for mono-methyl phthalate (MMP), mono-ethyl phthalate (MEP), and mono-ethylhexyl phthalate (MEHP), urinary median levels were significantly higher in the 7-17-year old group than in the ≧18-year-old group. For most phthalate metabolites and in the general population, the geometric mean decreased with increasing age. Median levels of MEP (19.55 μg/L), mono-benzyl phthalate (MBzP) (2.11 μg/L), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) (22.82 μg/L), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEOHP) (16.08 μg/L), ΣDibutyl phthalate metabolites (ΣDBPm) (0.17 nmol/mL), Σdi-(2-ethylhexyl) phthalate metabolites (ΣDEHPm) (0.29 nmol/mL) were higher in participants from central Taiwan than those from other areas. The median level of DBP (ΣDBPm: 0.20 nmol/mL) was significantly higher in participants from harbor areas than those from other urbanization groups. The RV of the 95 percentile (P₉₅) for phthalate metabolites in the 7-17/≧18-year-old groups were 185.95/208.19 μg/L for MMP, 198.46/265.81 μg/L for MEP, 119.85/69.99 μg/L for mono-isononyl phthalate (MiBP), 165.19/204.32 μg/L for Mono-n-butyl phthalate (MnBP), 15.61/11.73 μg/L for MBzP, 62.09/59.23 μg/L for MEHP, 149.70/69.66 μg/L for MEHHP, 112.06/35.07 μg/L for MEOHP, 195.20/93.83 μg/L for mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), 45.66/27.69 μg/L for mono-(2-carboxymethylhexyl) phthalate (MCMHP), and 9.09/12.13 μg/L for mono-iso-nonyl phthalate (MiNP). We concluded that phthalate exposure of the general population in Taiwan varies by sex, age, region, and urbanization level. Exposure by the 7-17-year-old group to DMP, DBP, and DEHP in Taiwan remains higher than that of youth from other countries. RV of phthalate metabolites in Taiwan were established in the current study.

Bisphenol A as a Factor in the Mosaic of Autoimmunity

The population worldwide is largely exposed to bisphenol A (BPA), a commonly used plasticizer, that has a similar molecular structure to endogenous estrogens. Therefore, it is able to influence physiological processes in human body, taking part in the pathophysiology of various endocrinopathies, as well as, cardiovascular, neurological and oncological diseases. BPA has been found to affect the immune system, leading to the development of autoimmunity and allergies, too. In the last few decades, the prevalence of autoimmune diseases has significantly increased, that could be explained by a rising exposure of the population to environmental factors, such as BPA. BPA has been found to play a role in the pathogenesis of systemic autoimmune diseases and also organ-specific autoimmunity (thyroid autoimmunity, diabetes mellitus type 1, myocarditis, inflammatory bowel disease, multiple sclerosis, encephalomyelitis etc), but the results of some studies remain still controversial, so further research is needed.

Urinary Biomarkers of Phthalates Exposure, Blood Lead Levels, and Risks of Thyroid Nodules

Thyroid nodules (TNs) are becoming increasingly prevalent. However, few studies have reported the effects of phthalates and lead (Pb) on TNs. In this study, we aimed to explore the associations of phthalates and Pb with the risks of TN. We sex-age-matched 220 TNs patients and 220 healthy controls from Zhejiang Shangyu, China. We measured 13 phthalate metabolites in spot urine samples. Blood lead levels (BLLs) were determined by atomic absorption spectrometry. The multivariable logistic regression models were used to assess the associations between urinary phthalate metabolites and BLLs and the risks of TNs. We found BLLs were associated with increased risk of TNs in total population. Female-specific positive associations of mono-2-ethyl-5-carboxypentylphthalate (MECPP), mono-2-ethyl-5-hydroxyhexylphthalate (MEHHP), mono-2-ethyl-5-oxohexylphthalate (MEOHP), mono-2-carboxymethyl-hexyl phthalate (MCMHP), and mono-isononyl phthalate (MiNP) with increased risk of TNs were also observed. Moreover, the positive association between phthalates and TNs was modified by BLLs. At the highest tertile of BLLs, monoethylphthalate (MEP), MECPP, MEHHP, MEOHP, and MiNP were significantly associated with increased risk of TNs. Our results indicated that certain phthalate metabolites and BLLs may contribute to increased risks of TNs.

Maternal Thyroid Disorders and Risk of Autism Spectrum Disorder in Progeny

BACKGROUND

Maternal thyroid dysfunction is suspected of causing adverse neurodevelopmental effects, but current evidence is inconclusive. Epidemiologic investigations generally suggest an association between maternal thyroid dysfunction and neurodevelopment impairments in progeny, but clinical trials of thyroid treatment during pregnancy reported null effects. To better understand these discrepant findings, we evaluated the association between maternal thyroid conditions and autism spectrum disorder (ASD), including examining the role of gestational thyroid-related hormone concentrations and thyroid medications use.

METHODS

Analyses considered 437,222 singleton live births occurring in a large Israeli health fund in 1999-2013, followed through 2016. Thyroid conditions and ASD cases were identified through International Classification of Diseases-9 codes with subsequent validation through review of medical records. Laboratory gestational thyroid hormone measurements were also considered.

RESULTS

Children of mothers who ever experienced hypothyroidism had a higher risk of ASD compared with children of mothers without hypothyroidism (adjusted odds ratio [aOR] = 1.26, 95% confidence interval [CI] = 1.12, 1.42). The association with hyperthyroidism was less consistent, but elevated in main analyses (aOR = 1.42, 95% CI = 1.04, 1.94). These associations were not explained by maternal gestational thyroid hormones levels nor mitigated by gestational use of thyroid medications.

CONCLUSIONS

Results indicate that maternal thyroid conditions are associated with increased ASD risk in progeny, but suggestively not due to direct effects of thyroid hormones. Instead, factors that influence maternal thyroid function could have etiologic roles in ASD through pathways independent of maternal gestational thyroid hormones and thus be unaffected by medication treatment. Factors known to disrupt thyroid function should be examined for possible involvement in ASD etiology.

The Association of Bisphenol A and Phthalates with Risk of Breast Cancer: A Meta-Analysis

Background: Breast cancer is the most common cancer and the second leading cause of cancer-related death amongst American women. Endocrine-disrupting chemicals (EDCs), especially bisphenol A (BPA) and phthalates, have adverse effects on human health. However, the association of BPA and phthalates with breast cancer remains conflicting. This study aims to investigate the association of BPA and phthalates with breast cancer. Methods: Correlative studies were identified by systematically searching three electronic databases, namely, PubMed, Web of Sciences, and Embase, up to November 2020. All data were analyzed using Stata 15.0. Results: A total of nine studies, consisting of 7820 breast cancer cases and controls, were included. The urinary phthalate metabolite mono-benzyl phthalate (MBzP) and mono-2-isobutyl phthalate (MiBP) were negatively associated with breast cancer (OR = 0.73, 95% CI: 0.60–0.90; OR = 0.75, 95% CI: 0.58–0.98, respectively). However, the overall ORs for BPA, mono-ethyl phthalate (MEP), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-2-ethylhexyl phthalate (MEHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono-(3-carboxypropyl) phthalate (MCPP), and mono-butyl phthalate (MBP) were 0.85 (95% CI: 0.69–1.05), 0.96 (95% CI: 0.62–1.48), 1.12 (95% CI: 0.88–1.42), 1.13 (95% CI: 0.74–1.73), 1.01 (95% CI: 0.74–1.40), 0.74 (95% CI: 0.48–1.14), and 0.80 (95% CI: 0.55–1.15), respectively, suggesting no significant association. The sensitivity analysis indicated that the results were relatively stable. Conclusion: Phthalate metabolites MBzP and MiBP were passively associated with breast cancer, whereas no associations were found between BPA, MEP, MEHHP, MEHP, MEOHP, MCPP, and MBP and breast cancer. More high-quality case-control studies or persuasive cohort studies are urgently needed to draw the best conclusions.

Urinary phthalate metabolite concentrations, oxidative stress and thyroid function biomarkers among patients with thyroid nodules

Prior human studies have explored effects of phthalate exposures on thyroid function, but the underlying biological mechanisms remain poorly unclear. We aimed to explore the associations between phthalate exposures and thyroid function among a potentially susceptible population such as patients with thyroid nodules, and further to assess the mediating role of oxidative stress. We measured eight phthalate metabolites, three oxidative stress biomarkers [8-hydroxy-2-deoxyguanosine (8-OHdG), 8-iso-prostaglandin F_2α (8-isoPGF_2α) and 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA)] in urine and three thyroid function biomarkers [thyroid-stimulating hormone (TSH), free triiodothyronine (FT3) and free thyroxine (FT4)] in serum among 214 patients with thyroid nodules. Multivariate regression models were applied to assess the associations among urinary phthalate metabolites, oxidative stress and thyroid function biomarkers. The potential mediating role of oxidative stress was explored by mediation analysis. We observed that multiple urinary phthalate metabolites were associated with altered FT4 and increased oxidative stress biomarkers (all FDR-adjusted P ≤ 0.05). Meanwhile, we found that 8-isoPGF_2α was negatively associated with FT3/FT4 among patients with benign thyroid nodules (FDR-adjusted P = 0.08). The mediation analysis indicated that 8-isoPGF_2α mediated the associations of urinary MEHHP and %MEHP with FT3/FT4, with 55.6% and 32.6% proportion of the mediating effects, respectively. Our data suggest that lipid peroxidation may be an intermediate mechanism involved in the effects of certain phthalate exposures on altered thyroid function among patients with benign thyroid nodules.

Gestational Exposure to Phthalates and Social Responsiveness Scores in Children Using Quantile Regression: The EARLI and HOME Studies

Linear regression is often used to estimate associations between chemical exposures and neurodevelopment at the mean of the outcome. However, the potential effect of chemicals may be greater among individuals at the 'tails' of outcome distributions. Here, we investigated distributional effects on the associations between gestational phthalate exposure and child Autism Spectrum Disorder (ASD)-related behaviors using quantile regression. We harmonized data from the Early Autism Risk Longitudinal Investigation (EARLI) (n = 140) Study, an enriched-risk cohort of mothers who had a child with ASD, and the Health Outcomes and Measures of the Environment (HOME) Study (n = 276), a general population cohort. We measured concentrations of 9 phthalate metabolites in urine samples collected twice during pregnancy. Caregivers reported children's ASD-related behaviors using the Social Responsiveness Scale (SRS) at age 3-8 years; higher scores indicate more ASD-related behaviors. In EARLI, associations between phthalate concentrations and SRS scores were predominately inverse or null across SRS score quantiles. In HOME, positive associations of mono-n-butyl phthalate, monobenzyl phthalate, mono-isobutyl phthalate, and di-2-ethylhexyl phthalate concentrations with SRS scores increased in strength from the median to 95th percentile of SRS scores. These results suggest associations between phthalate concentrations and SRS scores may be stronger in individuals with higher SRS scores.

Association of Phthalate Exposure with Thyroid Function and Thyroid Homeostasis Parameters in Type 2 Diabetes

AIMS

Phthalates, which are recognized environmental endocrine-disrupting chemicals, are associated with thyroid hormone disruption. We aimed to evaluate the relationship of phthalate metabolites with thyroid function and thyroid homeostasis parameters in type 2 diabetes and to explore whether thyroid autoimmunity status and metformin, the most common antidiabetic drug, may influence such associations.

METHODS

Concurrent urine and blood samples were collected from 639 participants with type 2 diabetes in the METAL (Environmental Pollutant Exposure and Metabolic Diseases in Shanghai) study. We measured urinary concentrations of thirteen phthalate metabolites along with serum levels of thyroid-stimulating hormone (TSH), total T₄ and T₃, free T₄ (FT₄) and T₃ (FT₃), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb). Four parameters of thyroid homeostasis, including the sum activity of step-up deiodinases (SPINA-GD), thyroid secretory capacity (SPINA-GT), Jostel's TSH index (TSHI), and thyrotroph thyroid hormone resistance index (TTSI), were also calculated.

RESULTS

Among all participants, after full adjustment, multivariable regression analysis showed that some urine phthalate metabolites were negatively associated with TSH, TSHI, and TTSI levels and positively associated with FT₃, T₃, SPINA-G_D, and SPINA-G_T levels. None of the urine phthalate metabolites exhibited a significant association with thyroid autoimmunity. The associations of phthalate metabolites with thyroid function and thyroid homeostasis parameters differed based on thyroid autoantibody and metformin treatment status.

CONCLUSIONS

Urinary phthalate metabolites may be associated with thyroid function and thyroid homeostasis parameters among participants with type 2 diabetes. Furthermore, our present study suggested that thyroid autoantibody status and metformin treatment status are potential mediators of such associations.

Data integration, analysis, and interpretation of eight academic CLARITY-BPA studies

"Consortium Linking Academic and Regulatory Insights on BPA Toxicity" (CLARITY-BPA) was a comprehensive "industry-standard" Good Laboratory Practice (GLP)-compliant 2-year chronic exposure study of bisphenol A (BPA) toxicity that was supplemented by hypothesis-driven independent investigator-initiated studies. The investigator-initiated studies were focused on integrating disease-associated, molecular, and physiological endpoints previously found by academic scientists into an industry standard guideline-compliant toxicity study. Thus, the goal of this collaboration was to provide a more comprehensive dataset upon which to base safety standards and to determine whether industry-standard tests are as sensitive and predictive as molecular and disease-associated endpoints. The goal of this report is to integrate the findings from the investigator-initiated studies into a comprehensive overview of the observed impacts of BPA across the multiple organs and systems analyzed. For each organ system, we provide the rationale for the study, an overview of methodology, and summarize major findings. We then compare the results of the CLARITY-BPA studies across organ systems with the results of previous peer-reviewed studies from independent labs. Finally, we discuss potential influences that contributed to differences between studies. Developmental exposure to BPA can lead to adverse effects in multiple organs systems, including the brain, prostate gland, urinary tract, ovary, mammary gland, and heart. As published previously, many effects were at the lowest dose tested, 2.5μg/kg /day, and many of the responses were non-monotonic. Because the low dose of BPA affected endpoints in the same animals across organs evaluated in different labs, we conclude that these are biologically - and toxicologically - relevant.

Bisphenol A and thyroid hormones: Bibliometric analysis of scientific publications

Bisphenol A (BPA) is a well-known endocrine-disrupting chemical which can cause potential health risks and interfere with thyroid hormones through multiple avenues. This study aimed to evaluate the hotspots and emerging trends on BPA and thyroid hormones by using a bibliometric method.Publications related on BPA and thyroid hormones were downloaded from Science Citation Index-Expanded database. Annual outputs, high yield journals, countries, institutions, authors and their cited times were summarized. In addition, keywords co-occurrence, burst references and citation networks were bibliometric analyzed.From 2000 to 2019, 418 articles were published. Both of the Environment International and Environmental Health Perspectives, United States, Chinese Academy of Sciences and Antonia M. Calafat were the most recorded journals, countries, institutions and authors, respectively. The main research area was Toxicology. In addition of the retrieve term "bisphenol-a" and "thyroid-hormone", "in-vitro", "exposure" and "endocrine disruptors", were the hotspot keywords and "triclosan", "oxidative stress" and "united-states" were the most recent trends keywords. "Thyroid hormone action is disrupted by Bisphenol A as an antagonist" published on The Journal of Clinical Endocrinology & Metabolism by Kenji Moriyama in 2002 got both the highest burst score and citation score. Six groups were clustered and the mechanism of BPA's effect on thyroid hormones, and the exposure of BPA and potential risks in children and pregnant women were the two main large fields.The number of publications in the field of BPA and thyroid hormones has increased tremendously since 2000. The research hotspot ranged from mechanism researches in animal models to epidemiological studies. "Thyroid hormone action is disrupted by bisphenol A as an antagonist" of Kenji Moriyama provided important building blocks in the field. The impact of BPA on thyroid hormones, especially pregnant women and children, was the latest research frontiers and might be the future direction of this filed in the following years.

Combined effects of di (2-ethylhexyl) phthalate and bisphenol A on thyroid hormone homeostasis in adolescent female rats

Phthalates and bisphenols are two typical classes of endocrine-disrupting chemicals (EDCs) which cause endocrine disorder in humans and animals. Phthalates and bisphenols are suggested to be associated with thyroid dysfunction. However, the effects of combined exposure and the detailed mechanisms are yet poorly understood. We investigated the combined effects of di (2-ethylhexyl) phthalate (DEHP) and bisphenol A (BPA) on thyroid function during puberty. Female Sprague Dawley rats were gavaged from postnatal 28 to 70 days with a single or combined exposure of DEHP (0, 150, and 750 mg/kg/day) and BPA (0, 20, and 100 mg/kg/day) according to a 3 × 3 factorial design. The thyroid weights reduced after combined exposure to the highest dose of DEHP and BPA, which noted their adverse effects on thyroid. Additionally, DEHP could increase the number of follicular epithelial cells in thyroid. Both DEHP and in combination with BPA could disturb the levels of thyroid hormones in serum, such as TT3 and TT4. Meanwhile, the possible mechanism was also discussed in the present study. DEHP treatment induced a significant increase of phosphorylation of cAMP-response element binding protein (Creb) via estrogen receptor α (Esr1), while the upregulation was nullified by the concomitant presence of BPA. In conclusion, the complex action of DEHP/BPA mixture may disturb the thyroid hormone homeostasis, which ultimately would affect the development of thyroid during puberty.

Meconium Exposure to Phthalates, Sex and Thyroid Hormones, Birth Size and Pregnancy Outcomes in 251 Mother-Infant Pairs from Shanghai

Phthalates are hormonally active pollutants. In-utero exposure to phthalates has been reported to be associated with birth size parameters and pregnancy outcomes. However, previous reports were inconsistent. We examined the associations between meconium exposure to phthalates and the effects on birth size parameters, pregnancy outcomes and sex and thyroid hormones in 251 mother–infant pairs from a Shanghai hospital. We measured 10 metabolites of phthalates in meconium samples collected during the first 24h after delivery. Information on seven birth size parameters (birth weight, birth length, abdominal circumference, head circumference, femur length, biparietal diameter and anogenital distance) and three pregnancy outcomes (gestational diabetes, premature rupture of membrane, and premature birth) was available from the birth record. Concentrations of free testosterone, estradiol (E2), thyroid stimulating hormone, concentrations of total and free thyroxine and triiodothyronine were measured from cord blood. Multivariate linear regression and logistic regression were used to estimate associations between phthalate exposure and health outcomes. mono-iso-butylphthalate (MiBP), mono-n-butylphthalate (MnBP) and mono-2-ethyl-5-oxohexyl phthalate (MEOHP) were positively associated with birth length and femur length which seemed more obvious in female newborn; MiBP, MnBP and mono-2-ethylhexylphthalate (MEHP) were positively associated with gestational diabetes mellitus (GDM) only in mothers with male newborns; monomethyl phthalate (MMP), MiBP and MEOHP were positively associated with E2 in male newborns. This study indicates that meconium exposure to phthalates may adversely affect some fetal growth parameters and GDM with a potential gender effect.

Prenatal and early childhood phthalate exposures and thyroid function among school-age children

BACKGROUND

Limited studies have investigated the association between prenatal and early childhood phthalate exposures and thyroid function among children.

OBJECTIVES

To investigate the association between early life phthalate exposure and thyroid function among school-age children, considering both prenatal and early childhood exposures, using longitudinal data from an established prospective cohort.

METHODS

We measured urinary phthalate metabolite levels during pregnancy and at 2, 4, and 6 years of age and conducted thyroid function tests at 6 years of age. We assessed the associations between phthalate metabolite levels and thyroid function using linear regression and Bayesian kernel machine regression (BKMR) models (n = 492).

RESULTS

In linear regression models, a doubling of urinary mono-n-butyl phthalate (MnBP) levels, measured during pregnancy and at 4 years of age, was associated with lower thyroid-stimulating hormone (TSH) levels at 6 years of age (-5.0%, 95% confidence interval [CI]: -8.8%, -1.0% and -5.7%, 95% CI: -9.7%, -1.5%, respectively). A similar association was found between mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) levels at 4 years of age and TSH levels at 6 years of age (-5.5%, 95% CI: -9.7%, -1.1%). Urinary mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) (2.3%, 95% CI: 0.1%, 4.5%) and MEOHP levels at 2 years of age (2.2%, 95% CI: 0.1%, 4.4%) and mono-2-ethyl-5-carboxypentyl phthalate (1.4%, 95% CI: 0.1%, 2.7%) and mono-benzyl phthalate levels at 6 years of age (1.1%, 95% CI: 0.4%, 1.9%) were associated with higher triiodothyronine (T3) levels at 6 years of age. Urinary MnBP during pregnancy, MEHHP, MEOHP, and MnBP at 4 years of age were also associated with lower free thyroxine (fT4) × TSH. In BKMR models, urinary MnBP levels during pregnancy were associated with lower TSH levels and fT4 × TSH (both posterior inclusion probabilities: 0.99).

CONCLUSIONS

Our findings suggest that early life phthalate exposure influences subsequent thyroid function. However, the results should be interpreted cautiously, because a single spot urine sample was used to quantify the phthalate exposures at each time point.

Mediating role of oxidative/nitrosative stress biomarkers in the associations between phthalate exposure and thyroid function in Taiwanese adults

Phthalate exposure was shown to alter thyroid function, however it is unclear, whether oxidative and nitrosative stress explains the intermediate biological mechanism. This study aimed to investigate the associations between phthalate exposure, oxidative/nitrosative stress, and thyroid function in adults, and to examine the mediating role of oxidative/nitrosative stress in the associations between phthalate exposure and thyroid function. Levels of eleven urinary phthalate metabolites, three urinary biomarkers of oxidative/nitrosative stress (malondialdehyde [MDA], 8-OHdG, and 8-NO₂Gua) and five serum thyroid hormones (thyroxine [T₄], free T₄, triiodothyronine, thyroid-stimulating hormone, and thyroxine-binding globulin) were measured in 266 Taiwanese adults. Cross-sectional associations between phthalate metabolites, biomarkers of oxidative/ nitrosative stress and thyroid hormones were analyzed using multivariate regression models. Mediation analysis was conducted to assess the role of oxidative/nitrosative stress in the associations between phthalate metabolites and thyroid hormone levels. Sum of di-(2-ethylhexyl) phthalate (DEHP) metabolites was positively associated with MDA (β_T1-T2 = 0.253, 95%CI [0.060, 0.447]; β _{≧ T2} = 0.317, 95% CI [0.098, 0.536]; P_trend = 0.005) and 8-NO₂Gua (β_T1-T2 = -0.010, 95%CI [-0.138, 0.118]; β _{≧ T2} = 0.144, 95% CI [-0.001, 0.289]; P_trend = 0.045). Mono-n-butyl phthalate (MnBP) was positively associated with 8-NO₂Gua (β_T1-T2 = 0.201, 95% CI [0.078, -0.324]; β _{≧ T2} = 0.161, 95% CI [0.031, -0.292]; P_trend = 0.018). T₄ was negatively associated with MDA (β_T1-T2 =  -0.027, 95% CI [-0.088, 0.0034]; β_≧T2 = -0.094, 95% CI [-0.161, -0.028]; P_trend = 0.005) and 8-NO₂Gua (β_T1-T2 = -0.068, 95% CI [-0.127, -0.010]; β_≧T2 = -0.125, 95% CI [-0.184, -0.066]; P_trend < 0.001). Free T₄ was positively associated with MDA (P_trend = 0.047) and with 8-NO₂Gua (P_trend < 0.001). 8-NO₂Gua mediated 11% of the association between the sum of DEHP metabolites and T₄, and 17% of the association between MnBP and free T₄. These results suggest that phthalate exposure may influence thyroid hormone levels through induced oxidative/nitrosative stress.

Thyroxine-binding globulin, peripheral deiodinase activity, and thyroid autoantibody status in association of phthalates and phenolic compounds with thyroid hormones in adult population

Exposure to consumer chemicals such as phthalates and phenolic compounds has been associated with thyroid hormone disruption in humans. However, information related to factors that may influence such associations, e.g., transport and activation of the hormones, and autoimmunity status, is limited. In the present study, we employed a subpopulation of adults (n = 1,254) who participated in the Korean National Environmental Health Survey (KoNEHS) 2015-2017, and associated urinary concentrations of major phthalate metabolites, bisphenol A (BPA), and parabens, with thyroid hormone-related measures, including free and total T3 and T4, TSH, thyroxine-binding globulin (TBG), calculated peripheral deiodinase (DIO) activity, and thyroid autoantibodies of thyroperoxidase (TPO) and thyroglobulin (Tg). Phthalate metabolites were negatively associated with total T4 and free T3, and positively associated with total T3. These observations could be explained by TBG levels and calculated peripheral DIO activity that were positively associated with phthalates exposure. In contrast, BPA was positively associated with total T4 and negatively associated with total T3, without any changes in TBG concentration. Serum TPO and Tg antibodies were not associated with urinary phthalate metabolites and BPA. However, thyroid autoantibody status appeared to modulate the association of some phthalates with thyroid hormones. For parabens, little to negligible association was observed. The results of our observation show potential underlying mechanisms of phthalates-induced thyroid hormone disruption, and suggests the importance of consideration of thyroid autoimmunity status in association studies for thyroid disrupting chemicals.