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Vitamin D

Vitamin D, which helps the body absorb calcium, is necessary for bone health. It's mostly accessible through sun exposure, not food. Too little vitamin D can contribute to osteoporosis and rickets in children. Some evidence suggests that the vitamin may reduce the risk of type 1 and 2 diabetes and multiple sclerosis, but the jury's still out on these benefits.

Bottom line: Even though very little sun is needed to get your quota of vitamin D, and some foods are fortified with it, deficiencies aren't unusual. Supplements might be a good idea, especially if you don't have much sun exposure, are over 50, or have dark skin.

Next: Vitamin E