A thyroid and antioxidant mineral that supports sperm — but only helps testosterone if you were deficient.
Selenium is a trace mineral your body uses to run its antioxidant defences (it's a building block of glutathione peroxidase), to regulate thyroid hormones, and to support healthy sperm production. The testes hold a lot of selenium, and it protects them from oxidative damage.
Only if you were short of it. Selenium supports the machinery around testosterone and sperm, but in men who already get enough, taking more does not raise testosterone — it just raises your risk of overdoing it. Correcting a genuine deficiency can help normalise hormone and sperm function; topping up an adequate diet won't. So this is a 'fill the gap' mineral, not a booster.
Selenium deficiency is uncommon in regions with selenium-rich soil but more likely with poor diets or certain gut conditions. Low thyroid function and poor sperm quality can be associated with low selenium.
Brazil nuts are in a class entirely of their own — just one or two can supply, or even exceed, a whole day's selenium, because the nuts concentrate it dramatically (which is also why a daily handful can tip you toward too much). After Brazil nuts, the richest sources are seafood (tuna, sardines, halibut, prawns and oysters), followed by organ and muscle meats, poultry, eggs, and then wholegrains, sunflower seeds and mushrooms. A crucial nuance most people don't realise: the selenium content of plant foods depends heavily on the soil they were grown in, so the same food can be selenium-rich or selenium-poor depending on region — this is exactly why deficiency clusters in certain parts of the world. For most people, one or two Brazil nuts a day is a complete, natural selenium strategy with no supplement needed.
The daily requirement is just 55 mcg. A modest supplement of 100–200 mcg/day covers gaps. The upper limit is 400 mcg/day from food and supplements combined — and this one matters, because selenium turns toxic above it.
Take it with food, daily. A couple of Brazil nuts is a natural source — but their selenium content is high and varies wildly, so a daily handful can push you past safe levels.
Selenium has a narrow safety window. Chronic excess (selenosis) causes hair and nail brittleness or loss, a garlic odour on the breath, digestive upset and nerve problems. More is genuinely harmful here.
It works alongside zinc and vitamin E for antioxidant and sperm support, on top of the core foundation. Don't stack several products that each contain selenium.
The main thing to avoid is doubling up: a multivitamin, a 'men's' formula and a separate selenium pill can quietly add up past 400 mcg. Check totals.
Anyone already taking a multivitamin or eating Brazil nuts daily, and anyone with thyroid disease (coordinate with your doctor). For most men a small dose is low-risk; the risk is from excess, not shortfall.
Selenomethionine is a well-absorbed form. Choose a modest, clearly dosed product (100–200 mcg), third-party tested, and check that your other supplements aren't already providing selenium.
Selenium is an essential antioxidant and sperm-support mineral that only helps testosterone if you were deficient — and it has a real toxicity ceiling. Keep total intake under 400 mcg/day, mind the Brazil nuts, and treat it as gap insurance rather than a booster.
NIH Office of Dietary Supplements — Selenium; reviews of selenium and male fertility; NHS — Selenium.
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Based on guidance from the NHS, NICE, Cleveland Clinic and peer-reviewed research.
General information, not a substitute for personal medical advice — always consult your doctor or a qualified health professional before making health decisions. If you are pregnant, breastfeeding, trying to conceive, under 18, or taking medication, speak to your doctor before starting any supplement.