How Does Selenium Affect Your Hormones?

October 29, 2025 •

4 min read

According to the National Institutes of Health, selenium is a vital trace mineral, but what does selenium do for your hormones? The thyroid gland contains the highest concentration of selenium in the body, which is crucial for producing and regulating thyroid hormones that control metabolism. Beyond its impact on the thyroid, selenium is essential for reproductive health and overall hormonal balance.

Quick Summary

Selenium plays a critical role in hormonal function, primarily by supporting the thyroid gland and protecting hormone-producing tissues from oxidative stress. It is integral to the conversion of thyroid hormones, aids male and female fertility, and helps regulate key sex hormones like testosterone, estrogen, and progesterone.

Key Points

Thyroid Hormone Conversion: Selenium is essential for the enzymes (deiodinases) that convert inactive T4 hormone into its active T3 form, regulating metabolism.
Antioxidant Protection: Selenoproteins protect hormone-producing glands, especially the thyroid and testes, from damaging oxidative stress.
Male Fertility Support: The mineral is critical for healthy testicular function, testosterone production, and improving sperm motility and quality.
Female Hormone Regulation: Selenium aids in the synthesis of estrogen and progesterone and helps protect eggs from oxidative damage during ovulation.
Autoimmune Modulation: Supplementation can reduce thyroid antibody levels and inflammation in autoimmune conditions like Hashimoto's thyroiditis.
Balanced Intake is Key: There is a narrow window between sufficient selenium intake and toxic levels (selenosis), emphasizing the need for appropriate dosage.
Rich Food Sources: Brazil nuts, seafood (tuna, halibut), meats, eggs, and grains are excellent dietary sources of selenium.

Selenium's Role in Thyroid Hormone Metabolism

Selenium is critical for the proper functioning of the thyroid, the master gland of metabolism. The thyroid gland is home to a high concentration of selenoproteins, which are enzymes that require selenium to work correctly. These selenoproteins are fundamental to thyroid hormone synthesis and metabolism.

Conversion of T4 to T3: Selenium-dependent deiodinase enzymes are responsible for converting the inactive thyroid hormone, thyroxine (T4), into the active hormone, triiodothyronine (T3). A selenium deficiency can impair this conversion, potentially leading to symptoms of hypothyroidism.
Antioxidant Protection: The process of producing thyroid hormones naturally generates reactive oxygen species (ROS), which can cause oxidative damage. Selenoproteins, particularly glutathione peroxidases, act as potent antioxidants, neutralizing these harmful free radicals and protecting the delicate thyroid tissue.
Reducing Autoimmune Attack: In autoimmune thyroid diseases like Hashimoto's and Graves' disease, selenium supplementation has been shown to reduce thyroid antibody levels (TPOAb), decrease inflammation, and improve patient quality of life, especially in selenium-deficient individuals.

Supporting Male Reproductive Health

Selenium is vital for male fertility and the production of sex hormones like testosterone. It's concentrated in the testes and is necessary for optimal sperm health and function.

Testosterone Production: Selenium helps maintain testicular tissue and protects the Leydig cells, which are responsible for testosterone synthesis, from oxidative damage. Some research indicates that selenium supplementation, particularly when combined with other antioxidants like zinc and vitamin E, may help increase testosterone levels.
Sperm Health: Oxidative stress is a known contributor to male infertility. Selenium acts as an antioxidant within the testes, reducing this stress and improving sperm motility, morphology, and overall quality. A deficiency is associated with impaired testicular function and reduced sperm parameters.

The Impact on Female Hormones

For women, selenium plays a multifaceted role in hormonal balance, from reproductive cycles to pregnancy.

Estrogen and Progesterone: Selenium is important for the production of female sex hormones, including estrogen and progesterone, which are crucial for fertility. Studies in rat models have also shown a relationship between estrogen status and selenium metabolism, suggesting that estrogen can influence the distribution of selenium throughout the body.
Ovulation and Egg Quality: As an antioxidant, selenium helps protect developing eggs (oocytes) from oxidative stress during maturation. This is particularly important for folliculogenesis and can impact fertility outcomes.
Polycystic Ovary Syndrome (PCOS): Low selenium levels are potentially linked with PCOS, a hormonal disorder impacting ovulation and menstrual regularity. While evidence is still developing, studies have shown that improving antioxidant status through selenium can benefit women with PCOS.
Pregnancy and Lactation: Adequate selenium is essential during pregnancy and lactation for both maternal and fetal health. It protects against oxidative stress in the placenta and aids lactation.

Comparison of Selenium's Hormonal Effects


Aspect	Thyroid Health	Male Hormonal Health	Female Hormonal Health
Primary Function	Cofactor for enzymes converting T4 to T3 and antioxidant protection of the gland.	Supports testosterone synthesis by protecting Leydig cells and improves sperm quality and motility.	Aids in the production of estrogen and progesterone, protects oocytes from damage, and supports pregnancy.
Key Hormones Involved	Thyroid hormones (T3 and T4).	Testosterone.	Estrogen and Progesterone.
Associated Conditions	Hypothyroidism, Hashimoto's thyroiditis, Graves' disease.	Infertility, low testosterone.	PCOS, infertility, pregnancy complications.
Mechanism	Integrated into selenoproteins, which act as deiodinases and glutathione peroxidases.	Antioxidant protection of testicular tissue and activation of signaling pathways.	Antioxidant protection of ovarian tissues and support for hormone-producing processes.

Sources and Supplementation

Most people can meet their selenium needs through a balanced diet, but intake can vary depending on the selenium content of the soil where food is grown. Animal products are generally reliable sources, while the selenium content of plant-based foods can be less consistent.

Food Sources: Excellent sources include Brazil nuts (but be mindful of high amounts), seafood (tuna, sardines, halibut), meats (beef, chicken), eggs, and whole grains.
Supplements: Supplementation may be necessary for those with deficiencies, which can be identified via testing. The recommended daily intake for adults is 55 micrograms, with a safe upper limit of 400 micrograms per day to avoid toxicity. It is crucial to consult a healthcare provider before starting supplementation. For those considering supplementing, it's worth noting the varying bioavailability of different forms, such as the organic selenomethionine found in yeast, which tends to be well-absorbed.

Conclusion

Selenium is far more than just a trace mineral; it's a fundamental regulator of the body's hormonal system. Its effects are most pronounced in the thyroid gland, where it is vital for the conversion and metabolism of thyroid hormones, protecting the gland from damaging oxidative stress. Beyond the thyroid, selenium plays a significant role in reproductive health for both men and women. It supports testosterone production and sperm quality in males, and aids in the synthesis of estrogen and progesterone while protecting egg quality in females. Ensuring adequate selenium intake, whether through food or mindful supplementation under medical guidance, is a key strategy for supporting hormonal balance and overall well-being. By understanding its powerful and multifaceted impact, we can appreciate the silent but essential role that selenium plays in our endocrine health. The importance of selenium for hormonal function is well-documented in scientific literature, and its antioxidative capabilities offer protection for numerous hormone-producing tissues.

Potential Risks and Considerations

While essential, excessive selenium intake can lead to toxicity, a condition called selenosis. Symptoms can range from hair loss, brittle nails, and gastrointestinal issues to more severe neurological problems. The narrow therapeutic window between deficiency and toxicity makes cautious supplementation critical, emphasizing the importance of testing and professional advice. High doses from supplements are the most common cause of toxicity, highlighting the need for careful sourcing and dosage.

Resources for Further Learning

Office of Dietary Supplements - Selenium Fact Sheet

Frequently Asked Questions

The thyroid hormones, T3 and T4, are most affected by selenium, as it is a necessary component of the enzymes that convert T4 to the active T3. It also plays a role in sex hormones like testosterone, estrogen, and progesterone.

Yes, adequate selenium intake can help with hormonal imbalances, particularly those involving the thyroid. It supports proper thyroid hormone metabolism and protects endocrine glands from damage, which can help regulate overall hormonal function.

Selenium is important for the production of female sex hormones, including estrogen and progesterone, and can affect how the body metabolizes selenium. Some studies suggest links between selenium and estrogen signaling, particularly in cancer research, but the full impact on overall estrogen levels in healthy individuals requires more study.

Yes, selenium is important for male reproductive health and may benefit testosterone production. It protects the testes and the testosterone-producing Leydig cells from oxidative stress and is essential for sperm quality.

Signs of a selenium deficiency that affect hormones can include fatigue, muscle weakness, infertility in both men and women, hair loss, and thyroid problems such as hypothyroidism.

To increase selenium intake, focus on eating a balanced diet rich in selenium-rich foods. Excellent sources include Brazil nuts (consume in moderation), seafood like tuna and sardines, meats, eggs, and whole grains. If you suspect a deficiency, consult a doctor about testing and potential supplementation.

Yes, excessive selenium intake can lead to toxicity, known as selenosis, which can disrupt normal bodily functions and potentially affect hormonal balance. It is crucial to stay within the recommended daily intake to avoid adverse effects.