What Selenium Does for Men's Health

Selenium is a mineral your body uses to build proteins called selenoproteins, which act as antioxidants and support your immune system. Men need 55 micrograms daily — the same amount as women, though some research suggests men may metabolize it differently. The mineral concentrates in the testes and prostate, which is why researchers have studied it most closely in male reproductive health and cancer prevention.

The evidence splits into three areas: sperm production, prostate health, and general antioxidant defense. Animal studies and small human trials show selenium supports sperm motility and count, but large randomized trials in men are sparse. For prostate cancer prevention, observational data suggested benefit in the 1990s, but a major 2014 trial found no reduction in prostate cancer risk at supplemental doses. What remains clear is that selenium deficiency impairs immune function and thyroid hormone metabolism in both sexes — and men with very low intake do show measurable changes in sperm quality.

Key Takeaways

  • Selenium supports sperm production and motility in animal models and small human studies, though large randomized trials confirming this in men are limited.
  • A major clinical trial found that selenium supplements did not reduce prostate cancer risk, contradicting earlier observational data that suggested a protective effect.
  • Most men in developed countries meet the 55-microgram daily requirement through food alone, particularly from seafood, poultry, and Brazil nuts.
  • Selenium deficiency is rare in North America but does impair immune response and thyroid function, affecting energy and infection recovery.
  • Doses above 400 micrograms daily can cause toxicity, leading to hair loss, brittle nails, and neurological symptoms.

How Selenium Supports Sperm Health

Selenium is a core component of glutathione peroxidase, an enzyme that protects sperm from oxidative damage. Sperm cells are particularly vulnerable to free radicals because they have high metabolic activity and limited antioxidant defenses of their own. When selenium levels are adequate, this enzyme works to prevent the lipid damage that can reduce sperm motility — the ability to swim toward an egg.

Animal studies consistently show that selenium deficiency reduces sperm count and movement. In human studies, men with low selenium intake or blood levels show lower sperm motility compared to men with adequate intake. A 2020 meta-analysis of observational studies found that men with higher selenium levels had better sperm parameters overall. However, these are correlational findings; no large randomized trial has yet shown that giving selenium supplements to men with normal intake improves fertility outcomes. For men with documented deficiency, correction does appear to improve sperm quality, but supplementation beyond normal dietary intake has not been proven to enhance fertility in men who already meet the requirement.

Selenium and Prostate Health: What the Research Actually Shows

In the 1990s, observational studies suggested that men with higher selenium levels had lower prostate cancer rates. This led to the Selenium and Vitamin E Cancer Prevention Trial (SELECT), a large randomized trial that ran from 2001 to 2011 and enrolled over 35,000 men. Researchers gave some men selenium supplements (200 micrograms daily) and others a placebo, then tracked cancer rates over an average of five years.

The trial found no difference in prostate cancer risk between the selenium group and placebo group. In fact, men taking selenium showed a slight (non-significant) increase in high-grade prostate cancer. This result contradicted the earlier observational data and led most cancer organizations to conclude that selenium supplements do not prevent prostate cancer. The discrepancy likely reflects a limitation of observational studies: men with higher selenium intake may differ in other health behaviors that actually drive the lower cancer rates, rather than selenium itself being protective.

Current evidence does not support selenium supplementation as a prostate cancer prevention strategy. Men concerned about prostate health should focus on established risk factors — family history, age, and race — and discuss screening options with their doctor rather than relying on mineral supplements.

Immune Function and Thyroid Health

Selenium is essential for making thyroid peroxidase and other enzymes that regulate thyroid hormone production and metabolism. Men with low selenium intake show reduced thyroid hormone conversion and slower immune response to infection. In studies of men with selenium deficiency, supplementation restores both thyroid function and the ability of immune cells to multiply and respond to pathogens.

This matters most for men in regions where soil selenium is very low — parts of Europe, China, and some areas of the United States. In North America, deficiency is uncommon unless a man has severe malabsorption, is on long-term dialysis, or follows a very restricted diet. For men with adequate intake, additional selenium does not further boost immune function. The practical takeaway is that meeting the 55-microgram daily requirement protects immune and thyroid health; more does not mean better.

Food Sources and How Much Men Actually Need

A single Brazil nut contains 60 to 90 micrograms of selenium — more than the daily requirement in one nut. Other reliable sources include oysters and other shellfish (40 to 60 micrograms per 3-ounce serving), turkey and chicken (22 to 35 micrograms per 3-ounce serving), and eggs (15 micrograms per large egg). Whole grains, brown rice, and legumes contain moderate amounts, though the content depends on soil selenium where they were grown.

Most men in the United States, Canada, and Western Europe meet the 55-microgram daily requirement through normal eating without tracking or supplementing. A man who eats poultry twice a week, includes seafood once weekly, and eats whole grains regularly will almost certainly be adequate. Men who follow very restricted diets — such as those avoiding all animal products and living in low-selenium regions — may need to pay attention, but even vegetarians can meet the requirement through Brazil nuts, seeds, and whole grains.

Risks of Too Much Selenium

Selenium toxicity occurs at doses above 400 micrograms daily over extended periods. Early signs include brittle hair and nails, a garlic-like odor on the breath and skin, and fatigue. With continued high intake, men may experience tremor, peripheral neuropathy (nerve damage in the hands and feet), and cognitive changes. Selenium toxicity is rare from food alone but can occur with high-dose supplements, particularly if a man takes multiple supplements containing selenium without checking the total.

The upper safe limit set by the National Institutes of Health is 400 micrograms daily for adults. Men taking supplements should check labels and avoid combining multiple products that each contain selenium. If a man is considering a supplement, 200 micrograms daily is a common dose in research studies, but this exceeds the requirement and offers no proven benefit over meeting the 55-microgram target through food.

When Supplementation Might Matter

Supplementation is most relevant for men with documented deficiency — confirmed by blood testing — or those with conditions that impair selenium absorption. Crohn's disease, celiac disease, and cystic fibrosis can reduce selenium uptake. Men on long-term dialysis lose selenium and may benefit from supplementation under medical supervision. Men following very low-calorie diets or living in regions with severely depleted soil selenium may also warrant supplementation, though this is uncommon in developed countries.

For men with normal intake and no malabsorption, the evidence does not support supplementation for fertility, prostate cancer prevention, or general health. The focus should be on meeting the requirement through food, which is straightforward and carries no toxicity risk. If a man is considering a supplement for any reason, discussing it with a doctor or registered dietitian first ensures it will not interact with medications or exceed safe limits.

Frequently Asked Questions

Does selenium improve erectile function?

No large randomized trials have tested this. Some animal studies suggest selenium supports blood vessel function, which is relevant to erectile health, but human evidence is absent. Erectile dysfunction has many causes — cardiovascular health, hormones, medications, and psychological factors matter far more than a single mineral. A man concerned about erectile function should see a doctor rather than self-treating with supplements.

Can selenium supplements prevent male infertility?

For men with documented selenium deficiency, correction may improve sperm quality. For men with normal intake, supplementation has not been shown to improve fertility in randomized trials. If a man and his partner are having difficulty conceiving, a fertility specialist can order appropriate testing and recommend evidence-based treatment rather than guessing at mineral deficiencies.

How do I know if I have low selenium?

Blood selenium testing is available through a doctor, though it is not routinely ordered unless deficiency is suspected based on symptoms or risk factors. Symptoms of deficiency include fatigue, muscle weakness, and recurrent infections. Men in developed countries rarely have deficiency unless they have malabsorption, are on dialysis, or follow a very restricted diet. If concerned, a doctor can order testing rather than assuming deficiency.

Is it safe to take selenium every day?

Yes, up to 400 micrograms daily is considered safe for long-term use. However, most men do not need supplementation because they meet the 55-microgram requirement through food. Taking a supplement when you already have adequate intake does not provide additional benefit and increases the risk of exceeding the safe upper limit if combined with other supplements.

Should I take selenium with other vitamins?

Selenium works alongside vitamin E and other antioxidants, but taking them together as supplements has not been shown to provide more benefit than meeting requirements through food. The SELECT trial tested selenium and vitamin E together and found no cancer prevention benefit. If taking a multivitamin, check the selenium content to avoid exceeding 400 micrograms daily from all sources combined.