Effect of soy isoflavones on thyroid hormones in intact and ovariectomized cynomolgus monkeys (Macaca fascicularis)

The relationship between dietary inflammatory index values and thyroid function in the US adult population: An analysis of the NHANES 2007-2012 cohort

OBJECTIVE

Researchers have developed the Dietary Inflammatory Index (DII) as a tool to quantify the inflammatory potential of a given diet. Higher DII scores indicated a more proinflammatory diet. While inflammation is known to have a strong impact on thyroid function, the precise nature of the association between DII scores and thyroid function has yet to be clarified. This study was conducted with the goal of exploring this relationship in a representative population of adults from the United States.

METHODS

For this study, we used data from the National Health and Nutrition Examination Survey (NHANES). Standardized questionnaires were used to collect demographic and dietary data from the participants, and laboratory tests were used to collect data on the participants' thyroid parameters and other relevant data. Linear regression models and smoothed curve fitting were used to assess the relationship between DII scores and thyroid function, with weighted data analyses and subgroup analyses being conducted as appropriate.

RESULTS

In total, 7712 subjects were recruited from the NHANES 2007-2012 cohort. Their weighted mean age was 44.87 (0.47) years, mean DII score was 1.41 (0.05). Mean FT3 was 3.20 (0.01) pg/mL and mean TT4 was 7.81 (0.03) µg/dL. In adjusted analyses, higher DII values were related to increases in FT3 (β = .007; p = .027) and TT4 (β = .050; p = .005) levels. Subgroup analyses showed a negative correlation between FT3 levels and DII scores in a population with high urinary iodine concentrations.

CONCLUSION

These data indicate that the consumption of a more proinflammatory diet, as evidenced by elevated DII scores, is correlated with significant increases in FT3 and TT4 levels. However, for people with high urinary iodine concentrations, a more proinflammatory diet was associated with lower FT3 levels. Additional research will be vital to clarify the mechanistic basis for these findings.

Exploratory analysis of the associations between urinary phytoestrogens and thyroid hormones among adolescents and adults in the United States: National Health and Nutrition Examination Survey 2007-2010

Phytoestrogens are naturally plant-derived compounds that could bind to estrogen receptors and mimic estrogenic effects. Previous studies showed a positive association between phytoestrogens and hypothyroidism; however, little is known on phytoestrogens and thyroid hormones. This study was designed to investigate the associations between urinary phytoestrogens and thyroid hormone levels. Based on the US National Health and Nutrition Examination Survey (NHANES) 2007-2010, 4103 participants were recruited in this cross-sectional study. Linear regression models and multiple linear regressions models were applied to examine the relationships between urinary phytoestrogens and thyroid hormone levels. Urinary O-desmethylangolensin (O-DMA) was found to be correlated with serum FT₄ levels in the female 20-60-year-of-age group (β=0.018, 95% CI: 0.006, 0.031). Higher enterolactone (ENT) levels were significantly positively associated with TSH levels in the 12-19-year-of-age female group (β=0.196, 95% CI: 0.081, 0.311). In the male group, enterodiol (END) was significantly positively correlated with TSH and TT₃ in the 12-19-year-of-age group, respectively (TT₃: β=3.444, 95% CI: 0.150, 6.737; TSH: β=0.104, 95% CI: 0.005, 0.203). However, equol (EQU) levels were negatively associated with TT₄ (12-19-year-of-age: β=- 0.166, 95% CI: - 0.279, - 0.034; 20-60-year-of-age: β=- 0.132, 95% CI: - 0.230, - 0.034). Our study provided epidemiological evidence that urinary phytoestrogens were powerfully associated with thyroid hormone levels. The results also supported that phytoestrogens acted as endocrine disruptors. It is imperative and important to pay attention to the intake of phytoestrogens.

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.

The comparison of the effect of soybean and fish oil on supplementation on menopausal symptoms in postmenopausal women: A randomized, double-blind, placebo-controlled trial

BACKGROUND

The effect of soybean and omega-3 fatty acid supplementation on menopausal symptoms in postmenopausal women was investigated.

MATERIALS AND METHODS

In a randomized, double-blind, placebo-controlled trial postmenopausal women were randomly given either soybean (Soygan 500 mg capsule; n = 60), or omega-3 fatty acids (Omega-rex 1000 mg soft gel; n = 60), or placebo (n = 60) daily for 12 weeks. The primary outcome was a change on the menopause rating scale score (MRS), while the secondary outcome was any adverse symptoms and effect was effect of soybean or omega-3 fatty acid supplements on the blood lipids and thyroid hormone.

RESULTS

Based on the results of post-hoc in terms of overall MRS score there was a significant difference between the control and Soygan (p < 0.001) and Omega-rex groups (p = 0.03); however, there was no significant difference between the two intervention groups (p = 0.86). Soygan and Omega-rex had no effects on the blood lipids and thyroid hormone.

CONCLUSION

Soygan and Omega-rex reduced the MRS score and improved menopausal symptoms in postmenopausal women.

Nutraceuticals in Thyroidology: A Review of in Vitro, and in Vivo Animal Studies

Nutraceuticals are defined as a food, or parts of a food, that provide medical or health benefits, including the prevention of different pathological conditions, and thyroid diseases, or the treatment of them. Nutraceuticals have a place in complementary medicines, being positioned in an area among food, food supplements, and pharmaceuticals. The market of certain nutraceuticals such as thyroid supplements has been growing in the last years. In addition, iodine is a fundamental micronutrient for thyroid function, but also other dietary components can have a key role in clinical thyroidology. Here, we have summarized the in vitro, and in vivo animal studies present in literature, focusing on the commonest nutraceuticals generally encountered in the clinical practice (such as carnitine, flavonoids, melatonin, omega-3, resveratrol, selenium, vitamins, zinc, and inositol), highlighting conflicting results. These experimental studies are expected to improve clinicians’ knowledge about the main supplements being used, in order to clarify the potential risks or side effects and support patients in their use.

Effects of isoflavones on breast tissue and the thyroid hormone system in humans: a comprehensive safety evaluation

Isoflavones are secondary plant constituents of certain foods and feeds such as soy, linseeds, and red clover. Furthermore, isoflavone-containing preparations are marketed as food supplements and so-called dietary food for special medical purposes to alleviate health complaints of peri- and postmenopausal women. Based on the bioactivity of isoflavones, especially their hormonal properties, there is an ongoing discussion regarding their potential adverse effects on human health. This review evaluates and summarises the evidence from interventional and observational studies addressing potential unintended effects of isoflavones on the female breast in healthy women as well as in breast cancer patients and on the thyroid hormone system. In addition, evidence from animal and in vitro studies considered relevant in this context was taken into account along with their strengths and limitations. Key factors influencing the biological effects of isoflavones, e.g., bioavailability, plasma and tissue concentrations, metabolism, temporality (pre- vs. postmenopausal women), and duration of isoflavone exposure, were also addressed. Final conclusions on the safety of isoflavones are guided by the aim of precautionary consumer protection.

Effects of Dietary Protein on Thyroid Axis Activity

Thyroid hormones (TH) are essential for the normal development and function of every vertebrate. The hypothalamic-pituitary-thyroid (HPT) axis is regulated to maintain euthyroid status. One of the most influential environmental factors that determines HPT axis activity is nutrition. Both food availability and substrate diversity affect thyroid hormone economy. The present paper aims to summarize literature data concerning the influence of the amount and the type of protein on thyroid axis activity. This review sheds light on the contribution of a low-protein diet or insufficient intake of essential amino acids to TH abnormalities. We believe that the knowledge of these dependencies could improve the results of nutritional interventions in thyroid axis disorders and enhance the efficiency of animal breeding.

Lifelong exposure to dietary isoflavones reduces risk of obesity in ovariectomized Wistar rats

SCOPE

Traditional Asian diet rich in soy isoflavones (ISOs) is discussed to be linked to a lower obesity prevalence. In lifelong and short-term exposure scenarios we investigated effects of an ISO-rich diet on the body composition and development of obesity in female rats.

METHODS AND RESULTS

Female Wistar rats grew up on ISO-free or ISO-rich control diet (CON ISO: 467 mg/kg diet). Starting postnatal day 83, ovariectomized and intact animals received high calorie Western diet (WD) in the absence or presence of ISO (WD ISO: 431 mg/kg diet) for 12 weeks to induce obesity or maintained on respective control diet (CON). One group starting ISO exposure after ovariectomy mimics short-term ISO exposure in postmenopausal Western women. Lifelong but not short-term ISO exposure resulted in reduced body weight, visceral fat mass, serum leptin, and smaller adipocytes. ISO decreased hepatic SREBP-1c, ACC, FAS, and PPARγ mRNA expression in nonobese animals. Moreover, ovariectomy reduced skeletal muscle weight, which was antagonized by both short-term and lifelong ISO exposure.

CONCLUSION

Our results indicate that in female rats lifelong but not short-term ISO intake reduces the risk to develop obesity. Furthermore, lifelong and short-term ISO exposure may antagonize loss of skeletal muscle mass induced by ovariectomy.