Selenium
Selenium (Se)
Minerals. Modern nutrition.
Also called Selenomethionine, Sodium selenite, Selenium yeast
Pinyin: xī
Spanish: Selenio
Hair loss at high dosesA trace mineral the body uses to make selenoproteins, which help the thyroid work and protect cells from damage.
Did you know? Brazil nuts are one of the richest sources of selenium, but the amount depends on the soil where the tree grew. One nut can cover a day's need, so eating many can be unsafe.
What it may help, and how strong the proof is
- Heart health. In parts of China with very low selenium in the soil, a heart muscle disease called Keshan disease was common. Selenium pills prevented it in trials. This effect is seen in deficiency. Extra selenium has not been shown to protect the heart in people who get enough.Strong proof
- Thyroid. Selenium is needed for thyroid enzymes. Some small trials in autoimmune thyroid disease (Hashimoto's) found lower thyroid antibodies with selenium, but clinical benefit is not clear.Early proof
- Colds, flu & immunity. Selenium helps immune cells work, and deficiency weakens them. Trials of extra selenium in people who are not low have not shown fewer infections.Traditional proof
Parts of the body
Traditional use
Brazil nuts have been eaten in the Amazon for generations, and they are among the world's richest selenium foods. Selenium was not identified as an essential nutrient until the 1950s.
How it is classified
- Herbal actions
- Nutritive, Antioxidant. Energy: neutral.
How people take it
Adults need 55 mcg a day (RDA). The upper limit is 400 mcg a day from food and pills. One Brazil nut can cover a day's need, and some nuts contain far more.
Food, tablet and capsule.
Where to get it
Good sources are Brazil nuts (very rich but variable), tuna, halibut, sardines, shrimp, lean beef and pork, turkey, chicken, eggs, cottage cheese, brown rice, and whole-wheat bread. Plant selenium depends on the soil. Pills come as selenomethionine, which is closer to food, or as sodium selenite.
Be careful
Selenium is safe at food amounts. Too much can cause hair loss, brittle nails, garlic breath, fatigue, nausea and nerve damage. Check multivitamin labels before adding extra selenium.
Avoid if: diabetes (high doses, ask a doctor).
Mixing with other things
- Worth knowingThyroid medicine (levothyroxine (Synthroid))
Selenium is part of the enzymes that make active thyroid hormone. People on thyroid medicine should not start high-dose selenium without a doctor.
- Worth knowing
Vitamin E and selenium both support antioxidant defenses. Pills of both did not prevent prostate cancer in the SELECT trial.
- Worth knowing
Iodine and selenium both support thyroid hormone production, and both are needed in balance.
The honest take
Selenium is needed in small amounts, and Brazil nuts show how a food can be too rich. Pills help people who are low, but extra selenium has not been shown to prevent cancer or heart disease in people who get enough. Some high-dose trials even linked it to more diabetes.