Selenium

Selenium is a trace mineral needed for thyroid hormone metabolism and antioxidant enzymes. Deficiency is uncommon in the U.S., since many foods contain it (including Brazil nuts, seafood and eggs). Evidence that selenium supplements improve fertility or reduce miscarriage in people who are not deficient is limited. More is not better: too much selenium is toxic.

People who have been advised to check their selenium intake, for example those with a restrictive diet. Whether it suits you depends on your health, medicines and test results — ask a clinician.

The recommended daily intake for adults is 55 mcg (60 mcg in pregnancy). The NIH upper limit is 400 mcg per day from all sources. Brazil nuts vary widely in selenium — a single nut can contain a large amount. Doses vary by product and person; this is not personal medical advice.

Selenium status changes over weeks to months.

Excess selenium can cause garlic breath, metallic taste, hair or nail changes, stomach upset and nerve effects.

Do NOT exceed 400 mcg per day from all sources. Count Brazil nuts and your prenatal vitamin toward your total.

Evidence level (our editorial summary, not a formal grading): Limited.

Pregnancy & breastfeeding: Selenium is part of normal prenatal nutrition; do not exceed the upper limit.

Medication interactions: May interact with some medicines, including certain chemotherapy drugs and blood thinners; ask a pharmacist.

Talk to a healthcare professional before use if you are pregnant, breastfeeding, planning pregnancy, have a medical condition, take any medicine, or are scheduled for surgery. Dietary supplements are not approved by the FDA for safety or effectiveness before they are sold, and quality varies between products.

Reliable sources to check: NIH Office of Dietary Supplements fact sheets · NCCIH Herbs at a Glance · MedlinePlus Herbs & Supplements · FDA — Dietary Supplements