Effect of Nitrates, Thiocyanates and Selenium on the Iron and Iodine Status of Postpartum Women

Serum selenium concentration in patients with autoimmune thyroid disease

Abstract.

Consumption of water contaminated by nitrate and its deleterious effects on the human thyroid gland: a review and update

Nowadays, the nitrates have been established as carcinogenic components due to the endogenous formation of N-nitroso compounds, however, the consumption of water contaminated with nitrates has only been strongly related to the presence of methemoglobinemia in infants, as an acute effect, leaving out other side effects that demand attention. The thyroid gland takes relevance because it can be altered by many pollutants known as endocrine disruptors, which are agents capable of interfering with the synthesis of hormones, thus far, it is known that nitrates may disrupt the amount of iodine uptake causing most of the time hypothyroidism and affecting the metabolic functions of the organism in all development stages, resulting in an important health burden for the exposed population. Here, this review and update highlighted the impact of consumption of water contaminated with nitrates and effects on the thyroid gland in humans, concluding that nitrates could act as true endocrine disruptor.

Association Between Serum Nitric Oxide Level and Changes in Thyroid Function Test in a Population-based Study: Tehran Thyroid Study Participants (TTS)

BACKGROUND

Nitric oxide (NO) plays a key role in thyroid function regulation through the inhibition of iodide (I) uptake at the thyroidal sodium-iodide symporter (NIS) and impacts on the thyroid vascularity and blood flow.

OBJECTIVES

This study aimed to evaluate the association between serum NO metabolites (NOx) and thyroid-stimulating hormone (TSH), free thyroxin (FT4), and anti-thyroid peroxidase (TPOAb) changes. Also, it aimed at evaluating the correlation between serum NOx and the incidence of clinical hypothyroidism, characterized by elevated TSH level and decreased FT4 concentration, and subclinical hypothyroidism, characterized by mildly elevated TSH level despite FT4 concentration within the normal range, over three years of follow-up.

METHODS

This study included 1,137 participants of the Tehran Thyroid study (TTS), aged > 20 years old, for whom data on serum TSH, FT4, and TPOAb in the third and fourth phases, and serum NOx in the third phase were available. Changes in TSH (ΔTSH), FT4 (ΔFT4), and TPOAb (ΔTPO) between the third and fourth phases were calculated, and the associations between serum NOx and ΔTSH, ΔFT4, and ΔTPOAb were assessed after multivariable adjustment using linear regression analysis.

RESULTS

No significant association was found between serum NOx and ΔTSH, ΔFT4, and ΔTPOAb after the multivariable adjustment; neither was any observed in TPOAb split groups after multivariable adjustment. No significant association was found between serum NOx tertiles and clinical and subclinical hypothyroidism incidence in the fourth phase of TTS.

CONCLUSIONS

There was no association between serum NOx levels and changes in TSH, FT4, and TPOAb and clinical and subclinical hypothyroidism incidence.

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.