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Selenium
A few fast facts: Women are up to eight times more likely than men to have thyroid problems, and your risk increases as you age and during and after pregnancy, Wagner says. So, once you're counting 30-something candles on your birthday cake, it's time to think (more) about your thyroid. Studies show that sufficient selenium is necessary for helping to prevent thyroid disease.

How much to take: The best way to take your selenium is—surprise!—by eating two Brazil nuts per day, says Wagner. The nuts pack two to three times the recommended daily amount of selenium (55 mcg), and are a safe way to get the right amount of the mineral, that just happens to be in food form.