Low-Level Environmental Lead Exposure and Dysglycemia in Adult Individuals: Results from the Canadian Health and Measure Survey 2007-2011

Assessing the impact of arsenic, lead, mercury, and cadmium exposure on glycemic and lipid profile markers: A systematic review and meta-analysis protocol

The toxicity of metals presents a significant threat to human health due to the metabolic changes they induce. Thus, it is crucial to understand the impact of exposure to toxic elements on glycemic and lipid profiles. To this end, we developed a systematic review protocol registered in PROSPERO (CRD42023393681), following PRISMA-P guidelines. This review aims to assess environmental exposure to arsenic, cadmium, mercury, and lead in individuals aged over ten years and elucidate their association with glycemic markers such as fasting plasma glucose, glycated hemoglobin, as well as lipid parameters including total cholesterol, triglycerides, high-density lipoprotein, and low-density lipoprotein cholesterol. Articles published in the MEDLINE (PubMed), EMBASE, Web of Science, LILACS, and Google Scholar databases until March 2024 will be included without language restrictions. The modified Newcastle-Ottawa scale will be employed to assess the quality of the included studies, and the results will be presented through narrative synthesis. If adequate data are available, a meta-analysis will be conducted. This review can help understand the metabolic responses to exposure to toxic elements and the associated health risks.

Consequences of Disturbing Manganese Homeostasis

Manganese (Mn) is an essential trace element with unique functions in the body; it acts as a cofactor for many enzymes involved in energy metabolism, the endogenous antioxidant enzyme systems, neurotransmitter production, and the regulation of reproductive hormones. However, overexposure to Mn is toxic, particularly to the central nervous system (CNS) due to it causing the progressive destruction of nerve cells. Exposure to manganese is widespread and occurs by inhalation, ingestion, or dermal contact. Associations have been observed between Mn accumulation and neurodegenerative diseases such as manganism, Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. People with genetic diseases associated with a mutation in the gene associated with impaired Mn excretion, kidney disease, iron deficiency, or a vegetarian diet are at particular risk of excessive exposure to Mn. This review has collected data on the current knowledge of the source of Mn exposure, the experimental data supporting the dispersive accumulation of Mn in the brain, the controversies surrounding the reference values of biomarkers related to Mn status in different matrices, and the competitiveness of Mn with other metals, such as iron (Fe), magnesium (Mg), zinc (Zn), copper (Cu), lead (Pb), calcium (Ca). The disturbed homeostasis of Mn in the body has been connected with susceptibility to neurodegenerative diseases, fertility, and infectious diseases. The current evidence on the involvement of Mn in metabolic diseases, such as type 2 diabetes mellitus/insulin resistance, osteoporosis, obesity, atherosclerosis, and non-alcoholic fatty liver disease, was collected and discussed.

Low-level lead exposure promotes hepatic gluconeogenesis and contributes to the elevation of fasting glucose level

BACKGROUND

Lead (Pb) is considered an endocrine-disrupting chemical. However, few studies have investigated the effects of low-level Pb exposure on plasma glucose levels. Herein, we aimed to investigate whether low-level Pb exposure causes elevated plasma glucose levels and the possible mechanisms involved.

METHODS

We conducted a cross-sectional study of 5747 participants from 16 sites in China. The participants underwent measurements of anthropometric factors, blood lead level (BLL) and fasting plasma glucose (FPG). Wistar rats were exposed to 0.05% Pb through drinking water or fed with a high-fat diet (HFD) for 28 weeks. The relevant parameters of glucose homeostasis, hepatic glucose production (HGP) and gene expression levels of hepatic gluconeogenesis enzymes, including phosphoenolpyruvate carboxy kinase (PEPCK), glucose-6-phosphatase (G6PC) and fructose-1,6-bisphosphatase (FBP1), were measured. In addition, gene expression levels of gluconeogenesis enzymes were also measured in HepG2 cells administered with different concentrations of lead acetate for 24 h.

RESULTS

In humans, after adjusting for confounders, the odds of having High_FPG (≥5.6 mmol/L) were significantly increased by 25% in the participants in the fourth BLL quartile (OR 1.25, 95% CI 1.05, 1.49). In the animals exposed to 0.05% Pb, FPG, HGP and hepatic gene expression levels of PEPCK, G6PC and FBP1 were increased. In addition, the mRNA expression levels of PEPCK, G6PC and FBP1 in HepG2 cells were also increased in response to Pb exposure.

CONCLUSIONS

These findings support the possibility that low-level Pb exposure may increase HGP by affecting key enzymes of hepatic gluconeogenesis, eventually resulting in impaired FPG and hyperglycemia.

Associations between metabolic syndrome and four heavy metals: A systematic review and meta-analysis

Four most concerned heavy metal pollutants, arsenic, cadmium, lead, and mercury may share common mechanisms to induce metabolic syndrome (MetS). However, recent studies exploring the relationships between MetS and metal exposure presented inconsistent findings. We aimed to clarify the relationship between heavy metal exposure biomarkers and MetS using a meta-analysis and systematic review approach. Literature search was conducted in international and the Chinese national databases up to June 2020. Of selected studies, we extracted the relevant data and evaluated the quality of each study's methodology. We then calculated the pooled effect sizes (ESs), standardized mean differences (SMDs), and their 95% confidence intervals (CIs) using a random-effect meta-analysis approach followed by stratification analyses for control of potential confounders. Involving 55,536 participants, the included 22 articles covered 52 observational studies reporting ESs and/or metal concentrations on specific metal and gender. Our results show that participants with MetS had significantly higher levels of heavy metal exposure [pooled ES = 1.16, 95% CI: 1.09, 1.23; n = 42, heterogeneity I2 = 75.6%; and SMD = 0.22, 95% CI: 0.15, 0.29; n = 32, I2 = 94.2%] than those without MetS. Pooled ESs in the subgroups stratified by arsenic, cadmium, lead, and mercury were 1.04 (95% CI: 0.97, 1.10; n = 8, I2 = 61.0%), 1.10 (0.95, 1.27; 11, 45.0%), 1.21 (1.00, 1.48; 12, 82.9%), and 1.26 (1.06, 1.48; 11, 67.7%), respectively. Pooled ESs in the subgroups stratified by blood, urine, and the other specimen were 1.22 (95% CI: 1.08, 1.38; n = 26, I2 = 75.8%), 1.06 (1.00, 1.13; 14, 58.1%), and 2.41 (1.30, 4.43; 2, 0.0%), respectively. In conclusion, heavy metal exposure was positively associated with MetS. Further studies are warranted to examine the effects of individual metals and their interaction on the relationship between MetS and heavy metals.

The effect of crocin supplementation on lipid concentrations and fasting blood glucose: A systematic review and meta-analysis and meta-regression of randomized controlled trials

OBJECTIVE

This meta-analysis aimed to assess the effects of crocin supplementation on fasting blood glucose (FBG) and lipid profile levels in clinical trial studies.

DESIGN

A systematic literature search was performed in PubMed, Scopus, Embase, Web of Science, and the Cochrane Library databases for clinical trials published from the beginning up to November 2019. Of the 547 papers identified from all searched databases, eight eligible studies with nine effect sizes have all needed criteria for inclusion in this meta-analysis.

RESULTS

Results of the pooled random-effect size analysis showed just a significant decreasing effect of crocin supplementation on FBG (WMD: -6.52 mg/l, 95 % CI, -11.96, -1.08; p = 0.019) and TC (WMD: -4.64 mg/l, 95 % CI, -8.19, -1.09; p = 0.010). Crocin supplements did not have any significant effect on serum TG (p = 0.144) levels, LDL-C (p = 0.161), and HDL-C (p = 0.872) levels. Results showed that crocin supplementation could beneficially have effect on TG level only when trial duration less than 12 weeks and LDL-C levels in trials that used high dose intervention and trials that conducted on subjects with metabolic disorders. However, crocin supplementation did not significantly change FBG in trials that used low dose intervention. Meta-regression analysis indicated a linear relationship between the duration of intervention and significant change in FBG (p = 0.019).

CONCLUSION

Results of this systematic review and meta-analysis study have shown that crocin supplementation can decrease significantly FBS and TC without any beneficial effects on TG, LDL-C, and HDL-C levels.

Efficacy and safety of Rhizoma curcumea longae with respect to improving the glucose metabolism of patients at risk for cardiovascular disease: a meta-analysis of randomised controlled trials

BACKGROUND

Clinical evidence suggests that curcuminoids, as a natural polyphenol, can provide support for cardioprotection and glucose metabolism. This meta-analysis assessed the efficacy and safety of curcumin with respect to improving glucose metabolism in patients with cardiovascular risk factors.

METHODS

Four databases (PubMed, Cochrane Library, Web of Science and Embase) were searched up to June 2018. The inclusion criteria included (i) randomised controlled trials (RCT) and (ii) subjects with risk factors for cardiovascular disease supplemented with curcumin and curcuminoids. A random-effects model and a standardised mean difference with a 95% confidence interval were used to perform quantitative data synthesis. Sensitivity and subgroup analyses were conducted to assess the effects.

RESULTS

Fourteen eligible RCT with 1277 subjects were included. In the overall analyses, curcumin led to significant decreases in fasting blood glucose (FBG), glycated haemoglobin (HbA1c) and homeostatic model assessment of insulin resistance (HOMA-IR). The subgroup analyses suggested that curcumin or combined curcuminoids were more effective at reducing FBG and HbA1c in type 2 diabetes patients than in individuals with metabolic syndrome. Supplementation with curcuminoids at doses ≥300 mg day^-1 showed significant decreases in FBG, HbA1c and HOMA-IR. The effects of supplementation on FBG, HbA1c and HOMA-IR were more significant over long periods (≥12 weeks) than short periods. Curcumin and curcuminoids were well tolerated, with no serious adverse events.

CONCLUSIONS

Curcumin or combined curcuminoids could exert cardioprotective effects in patients at risk for cardiovascular disease by improving glucose metabolism. However, further high-quality studies and larger sample sizes are required to confirm these results.

Associations of blood lead levels with reproductive hormone levels in men and postmenopausal women: Results from the SPECT-China Study

We examined whether blood lead levels (BLLs) were associated with reproductive hormone levels in a cross-sectional study using data from the SPECT-China study. We selected 2286 men and 1571 postmenopausal women without hormone replacement therapy. BLLs, blood cadmium, total testosterone (TT), oestradiol (E2), luteinizing hormone (LH), follicle stimulating hormone (FSH) and sex hormone binding globulin(SHBG) levels were measured. The results showed that median values (interquartile range) of BLLs were 44.00 μg/L (29.00–62.30) for men and 41.00 μg/L (27.00–59.81) for postmenopausal women. In linear regression, after adjusting for age, current smoking status, body mass index, systolic blood pressure, diabetes and blood cadmium level, TT (P for trend = 0.001) and SHBG (P for trend < 0.001) levels were still positively associated with BLLs in men. Meanwhile, significant positive associations were found for BLLs with SHBG (P for trend = 0.002), FSH (P for trend = 0.001) and LH (P for trend = 0.026) levels in postmenopausal women. Additionally, the association between BLL and SHBG was modified by dysglycaemia (P for interaction = 0.03) in postmenopausal women. In conclusion, BLLs were associated with reproductive hormone levels in the general population of Chinese men and postmenopausal women, which may have important implications for human health. Concerted efforts to reduce adult lead exposure are warranted.

Associations of Serum Manganese Levels with Prediabetes and Diabetes among ≥60-Year-Old Chinese Adults: A Population-Based Cross-Sectional Analysis

Older adults can experience glucose metabolism dysfunction, and although manganese may help regulate glucose metabolism, there is little information regarding this association among older people. This cross-sectional study included 2402 Chinese adults who were ≥60 years old in 2013 (Tianjin, China), and evaluated the associations of serum manganese with prediabetes and diabetes. Serum manganese levels were measured using inductively coupled plasma mass spectrometry. Multivariable logistic regression models were used to evaluate the sex-specific associations of manganese levels with diabetes and prediabetes after adjusting for confounding factors (age, sex, life style factors, and health status). Based on the WHO criteria, prediabetes was observed in 15.1% of men and 13.4% of women, while diabetes was observed in 30.0% of men and 34.4% of women. In the final model, the odds ratios (95% confidence interval) for prediabetes according to manganese quartile were 1.000, 0.463 (0.269–0.798), 0.639 (0.383–1.065), and 0.614 (0.365–1.031) among men and 1.000, 0.773 (0.498–1.200), 0.602 (0.382–0.947), and 0.603 (0.381–0.953) among women (p for trend = 0.134 and 0.015, respectively). The lowest prevalence of diabetes among men occurred at a moderate range of serum manganese (p < 0.05). Therefore, appropriate serum manganese levels may help prevent and control prediabetes and diabetes.