An essential trace mineral, selenium has a hand in fertility, hormone balance (especially thyroid), and DNA synthesis. Most of the body’s selenium is stored in muscle tissue.

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How much: Adults should aim for 55 micrograms (mcg) of selenium daily. Selenium can accumulate and cause toxicity; an excess can also contribute to brittle hair and nails.

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Best sources of selenium: The body easily and efficiently absorbs selenium from food, so most adults can get enough from a balanced diet. Foods high in selenium include tuna, halibut, and sardines.

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The best source of selenium, however, is Brazil nuts: A single nut contains 68 to 91 mcg of selenium. “You can get all the selenium you need by eating just one Brazil nut a day,” says Lisa Moskovitz, RD, CDN, author of The Core 3 Healthy Eating Plan. But keep it to one or two Brazil nuts to stay within the mineral’s tolerable upper limit.

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How to know if you’re low: A blood test can check your plasma for selenium status, which reflects short-term intake. Because much of the mineral is stored in muscle tissue, the body’s overall levels are hard to measure.

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Worth noting: Selenium levels decline with age, so consider including a high-quality multivitamin/multimineral in your routine. Some evidence suggests a link between low selenium and age-related declines in brain function, possibly because low levels means a loss of the mineral’s antioxidant benefits.

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This article was originally written by Catherine Guthrie, an Experience Life contributing editor and excerpted from the Experience Life article “5 Essential Minerals to Support Your Mind and Body.”