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Calcium

Our bodies need calcium—mostly found in dairy products like milk, yogurt, and cheese—to maintain healthy bones and prevent osteoporosis.

Bottom line: Supplements aren't a bad idea if you hate dairy (and can eat only so much kale and canned sardines), but you may want to skip them if you're prone to kidney stones or are a female over 70. A 2010 report linked supplements to heart-attack risk in older postmenopausal women. If you decide to go with supplements, don't take more than 500 milligrams at a time, and pair them with vitamin D to improve calcium absorption.

Next: Folic acid