Nutritional support for thyroid function
Thyroid dysfunctions impair physical and mental health, and their incidence is increasing in western countries, in part due to exposure to insidious environmental pollutants and widespread chronic stress. Diseases of the thyroid are typically classified as thyroid dysfunction; hypothyroidism and hyperthyroidism, or as structural disease presenting as nodules, goitre and cancer.
Autoimmune thyroid disease results from environmental factors (e.g. stress, environmental pollutants such as endocrine disrupting compounds, nutrient deficiency, iodine status, infections, certain drugs and pregnancy) triggering immune-endocrine interactions in genetically susceptible individuals. It is estimated that genetics contribute 70%-80% to the pathogenesis of autoimmune thyroid disease, while environmental factors contribute 20%-30%.
Nutritional support for the thyroid
Iodine – Iodine deficiency is the most common cause of hypothyroidism worldwide. Iodine is essential for thyroid hormone synthesis and is well known for its role in thyroid function. Deficiency may lead to low T4 levels, hence adequate intake should be ensured to maintain healthy thyroid function.
Selenium – The thyroid gland contains the highest concentration of selenium per gram of tissue. Adequate selenium is required for the function of iodothyronine deiodinases (DIOs) and conversion of T4 to T3. Therefore, deficiency in selenium can lead to decreased DIO enzyme function, decreased synthesis of thyroid hormone, and increased TSH production due to lack of negative feedback control and stimulation of the HPA axis.
In autoimmune thyroid disease, the benefits of selenium supplementation are thought to be due to modification of immune and inflammatory responses by enhancing glutathione peroxidase (GPX) and thioredoxin reductase (TR) activity, thus reducing oxidative stress, and toxic concentrations of hydrogen peroxide and lipid hydroperoxides that are produced from thyroid hormone synthesis.
Several studies have investigated the effects of selenium supplementation (100-200 µg/day) in autoimmune thyroid disease with many studies reporting reductions in inflammatory markers (antibodies).
Zinc – Preliminary evidence suggests that zinc may play a role in thyroid function by influencing aspects of peripheral thyroid hormone conversion. In addition, zinc appears to be involved in the formation and mechanism of action of thyrotropin-releasing hormone (TRH) and T3 binding to its nuclear receptor.
Vitamin D – A deficiency of vitamin D has been linked to a number of autoimmune conditions, including autoimmune thyroid disease. Several studies have shown that low vitamin D status is correlated with the presence of both Hashimoto’s thyroiditis and Grave’s disease, as well as TPO antibodies. Immunomodulatory and anti-inflammatory effects are likely to underlie the role of vitamin D in autoimmunity.
Vitamin A – Vitamin A has been shown to regulate thyroid hormone metabolism and inhibit TSH secretion via downregulation of TSH-ß gene expression. A deficiency of vitamin A may aggravate thyroid dysfunction caused by iodine deficiency, hence maintaining adequate intake is important.