From the Guidelines
Selenium supplementation in a 26-year-old female for 5 months could potentially contribute to a TSH drop to 0.38, as supported by a Danish RCT that showed selenium supplementation decreased TSH and FT4 concentrations in euthyroid subjects with marginal selenium deficiency 1. Selenium is an essential micronutrient that plays an important role in thyroid hormone metabolism, primarily through selenoproteins like deiodinases that convert T4 to the more active T3 hormone. When selenium intake increases, it can enhance thyroid hormone production and potentially lower TSH levels as part of the body's feedback mechanism. The normal TSH range is typically 0.4-4.0 mIU/L, so a level of 0.38 is just slightly below the conventional lower limit. If you're taking selenium supplements, typical doses range from 50-200 mcg daily, and exceeding this amount for extended periods could influence thyroid function. It's essential to consult with a healthcare provider about this TSH result, as other factors beyond selenium supplementation could be responsible, including autoimmune conditions, medication effects, or normal physiological variations. Your doctor may want to repeat the test or check free T3 and T4 levels to better understand your thyroid function before making any treatment decisions, considering the lack of direct evidence that treatment of thyroid dysfunction based on risk level alters final health outcomes 1. Key considerations include:
- The USPSTF found no direct evidence that treatment of thyroid dysfunction based on risk level alters final health outcomes 1
- The principal treatment for hypothyroidism is oral T4 monotherapy, while hyperthyroidism is treated with antithyroid medications or nonreversible thyroid ablation therapy 1
- Treatment is generally recommended for patients with a TSH level that is undetectable or less than 0.1 mIU/L, particularly those with overt Graves disease or nodular thyroid disease 1
From the Research
Selenium Supplementation and Thyroid Function
- Selenium supplementation has been associated with a reduction in TSH levels in some studies 2, 3, 4.
- A study published in the European Journal of Endocrinology found that selenium supplementation decreased serum TSH concentrations in a dose-dependent manner 2.
- A systematic review and meta-analysis of randomized clinical trials found that selenium supplementation decreased TSH levels in patients with Hashimoto thyroiditis without thyroid hormone replacement therapy 3.
- Another study found that selenium supplementation significantly decreased TPOAb, TGAb, and TSH levels in patients with Hashimoto's thyroiditis, accompanied by increased selenium, glutathione peroxidase 3, and selenoprotein P1 levels 4.
Effects of Selenium on TSH Levels
- The decrease in TSH levels associated with selenium supplementation may be dose-dependent, with higher doses resulting in greater reductions in TSH 2.
- The exact mechanism by which selenium supplementation affects TSH levels is not fully understood, but it may be related to the antioxidant properties of selenium and its role in thyroid hormone metabolism 5, 6.
- It is worth noting that the studies mentioned above were conducted in different populations and with varying doses and durations of selenium supplementation, which may affect the generalizability of the results.
Relevance to a 26-Year-Old Female
- While the studies mentioned above provide some insight into the effects of selenium supplementation on thyroid function, it is difficult to determine whether selenium supplementation would cause a specific individual's TSH level to drop to 0.38 without more information about the individual's health status, diet, and other factors that may influence thyroid function.
- However, based on the available evidence, it is possible that selenium supplementation could contribute to a decrease in TSH levels in some individuals, particularly those with autoimmune thyroiditis or other thyroid disorders 3, 4.