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Vitamin D
On the early end, this is the decade when the dreaded "p" word—perimenopause—could start showing up. After reaching your peak bone mass at around age 30, the "perimenopause years are really important for making strides to preserve bone health," says Wagner. While calcium is important, even more critical is vitamin D. One-quarter of women in this age group runs low in D, a vitamin that helps your body absorb calcium. If you have a family history of osteoporosis, ask your doctor if a calcium supplement is also needed, says Wagner; otherwise, turn to food sources, like green leafy vegetables or canned salmon for calcium. D is in some foods, like fortified dairy and canned sardines, but you may need a supplement to get your levels up, says Wagner.

How much to take: Aim for 1,000 to 2,000 IU daily. However, it's best to get a blood test at the doctor's office to check your levels before supplementing, as you may need a higher dose in the short-term, says Wagner.