Hyperthyroidism is a condition where the thyroid gland produces excessive hormones, accelerating the body’s metabolism. Selenium is an essential trace element obtained through diet, playing a role in protecting cells from damage and supporting thyroid hormone metabolism. The potential connection between selenium and hyperthyroidism is a subject of ongoing scientific interest.
Understanding Hyperthyroidism and Selenium’s General Role
Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone. This overproduction speeds up bodily systems, leading to symptoms such as nervousness, irritability, increased sweating, fine or brittle hair, weight loss despite increased appetite, and a rapid or irregular heartbeat. Graves’ disease, an autoimmune disorder, is the most common cause of hyperthyroidism, where antibodies mistakenly stimulate the thyroid.
Selenium is a trace mineral. It is incorporated into proteins called selenoproteins, which are involved in DNA synthesis, protection against cell damage, and the metabolism of thyroid hormones. The thyroid gland has the highest concentration of selenium per gram of tissue in the body. Within the thyroid, selenium-dependent enzymes, such as deiodinases and glutathione peroxidases, are crucial for converting thyroid hormones to their active forms and protecting the gland from oxidative stress generated during hormone production.
Scientific Insights on Selenium and Hyperthyroidism
Research into selenium’s role in hyperthyroidism, particularly Graves’ disease, explores its potential to modulate the immune response and reduce oxidative stress. Graves’ hyperthyroidism is associated with increased oxidative stress, and selenium, as an antioxidant, could help mitigate this. However, scientific findings on selenium’s direct impact on hyperthyroidism are not always consistent.
Some studies suggest selenium supplementation might improve certain aspects for patients with Graves’ disease. A meta-analysis indicated that selenium supplementation significantly decreased levels of free thyroxine (FT4) and free triiodothyronine (FT3) at three months, and thyroid-stimulating hormone receptor antibodies (TRAb) at six months, in Graves’ disease patients compared to placebo. Another trial suggested selenium could lead to faster attainment of normal thyroid function when combined with antithyroid drugs, especially in individuals with baseline selenium insufficiency.
Despite these observations, other randomized clinical trials have not consistently shown a beneficial effect of selenium on short-term control of hyperthyroidism or its clinical manifestations when patients already have sufficient selenium levels. For example, an Italian study found no short-term benefit for selenium supplements in Graves’ disease patients with adequate selenium levels. This suggests selenium’s effects might be more pronounced in populations with existing selenium deficiency.
It is important to distinguish selenium’s role in hyperthyroidism from its more established benefits in autoimmune hypothyroidism, specifically Hashimoto’s thyroiditis. In Hashimoto’s, selenium supplementation has been more consistently associated with a reduction in thyroid antibody levels and improved thyroid ultrasound features. For Graves’ orbitopathy (thyroid eye disease), a common extrathyroidal manifestation of Graves’ disease, some evidence suggests selenium supplementation can improve quality of life and reduce disease progression, particularly in mild cases.
Safe Use and Important Considerations
Obtaining selenium primarily through dietary sources is preferred. Foods rich in selenium include Brazil nuts, seafood (such as tuna and sardines), meat, poultry, eggs, and grains. Brazil nuts are an exceptionally concentrated source; just one to two nuts can provide the daily recommended intake of 55 micrograms (mcg) for adults. However, their selenium content can vary considerably depending on the soil where they are grown.
While selenium is essential, excessive intake can lead to toxicity, known as selenosis. Symptoms of selenosis include hair loss, brittle nails, gastrointestinal issues like nausea and diarrhea, fatigue, irritability, and a garlic-like odor on the breath. The tolerable upper intake level for selenium in adults is 400 mcg per day. Consuming amounts regularly above this limit, especially through high-dose supplements or excessive Brazil nut consumption, can lead to adverse effects.
Given the potential for toxicity and nuanced scientific findings, selenium supplementation for hyperthyroidism should only be considered under the direct supervision of a healthcare professional. Selenium is not a standalone treatment for hyperthyroidism and should not replace conventional medical therapies. Accurate diagnosis and ongoing medical management are crucial for individuals with hyperthyroidism. A healthcare provider can assess an individual’s selenium status and determine if supplementation is appropriate, ensuring safe and effective use alongside existing treatments.