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Skimp on styling. In your 40s, you may find that years of exposure to curling irons, hot blow dryers, and other gadgets have left your hair dried-out and brittle. The follicles at the front of your scalp can actually stop growing new hair from all the punishment, says dermatologist John Romano. The good news: The damage is reversible. Simply limit any hair-styling tool that puts off a lot of heat to special occasions or a few days a week. If you use a hair dryer every day, switch to a cooler or no-heat setting. And avoid excess brushing and washing, too, experts say.

Take your vitamins. It's normal to experience major fluctuations in hormone levels as you enter perimenopause, the 6 to 10 years before menopause. During this time, your hair may become finer and thinner. To counteract such changes, it can't hurt to ramp up your daily vitamin regimen. Start by adding 2,500 micrograms of biotin (some multivitamins contain this amount; check the label), a B vitamin that may strengthen the integrity of hair follicles and make strands less prone to breakage. In addition, omega-3 fatty acids, abundant in fish like salmon and tuna, may help stimulate hair growth; aim for two servings per week. Not a huge fish fan? Fish- or flaxseed-oil capsules also work well, says Heather Wickless, a dermatologist specializing in hair disorders. And if you're not already popping a women's multi, most docs say you should. The essential nutrients—like vitamins C, D, and E, and folic acid—will help keep your body and hair in good shape.

Talk about hair loss. Each strand of hair usually grows about an inch every two months for four years, then it falls out and is replaced by a new one. But in female pattern baldness, which affects up to 40% of women, hair begins to thin on the top of the scalp and sometimes all over the head. The problem is often inherited, but a hormone imbalance can also be a culprit. Fortunately, your doctor can recommend Women's Rogaine ($50 for a three-month supply), a topical solution that's applied directly to the area where thinning is occurring, or she can suggest other treatments to help stimulate new growth, says Peter Panagotacos, head of the department of dermatology at St. Mary's Medical Center in San Francisco.

Pack in protein. While you're making smart moves to protect your skin and bones from the natural effects of aging, keep your hair in mind, too. Protein goes a long way toward maintaining the strength and pliability of your hair—and most women don't get the recommended 37 to 50 grams per day. Get more protein from foods like tofu, lean meat, and eggs. Also, try a protein-infused styling product, such as Nexxus Y Serum Younger Looking Hair shampoo and conditioner ($24 and $33, respectively).