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The Wonders of Workouts continued...

According to scientists at the University of Pennsylvania, exercise during crucial bone-building years is the best predictor of a woman's adult bone health. Researchers tracked the diets and exercise habits of 81 girls from age 12 to age 18. (Women typically gain 40% to 50% of their total bone mass during these years.) In the end, those who saw the greatest bone gains were the girls who exercised the most, not those who consumed the most calcium.

"Exercise is more important than calcium," says Thomas Lloyd, PhD, lead author of the study. "By age 18 the game is over. You've got 98% of your bone mass," he says. "You may go on to gain 1% or 2% in your 20s, but it's inconsequential."

Too Little, Too Late?

But what about women, like myself, who frequented the library more than the athletic field -- are my bones a lost cause? Not so, says Lloyd.

Bone is like skin; it's constantly being regenerated. Kids need a lot of calcium because a bone's densest part, the core, is formed during adolescence. But adults need calcium, too. Even though the core gets thinner as we age, calcium from foods we eat is deposited on the surface of bones, like rings on a tree. As the rings grow, the bone's diameter expands, and it gets stronger.

Whether or not you get your calcium from dairy products, both sides of the debate agree that calcium is good no matter how it's delivered. "If you have an inclination to avoid dairy and get your calcium elsewhere, you certainly can," says Joan McGowan, PhD, director of the musculoskeletal diseases branch of the National Institutes of Health (NIH).

The growing popularity of calcium-fortified foods makes it easier than ever to meet your daily quota without dairy. The 300 milligrams of calcium that you'll find in one cup of milk can also be obtained by drinking the same amount of calcium-fortified orange juice or by eating a cup of dried figs or a bowl of Total cereal topped with calcium-enriched soy milk. Toss a half-cup of tofu (the kind made with calcium sulfate) into a stir-fry, and you've added a whopping 434 milligrams of calcium to your day. Other calcium-rich foods include collard greens (226 milligrams per serving), baked beans (127 milligrams), kale (94 milligrams), and broccoli (72 milligrams).

Daily calcium recommendations from the National Academy of Sciences start at 1,300 milligrams for adolescents ages 9 to 18, fall to 1,000 milligrams for adults ages 19 to 50, and, finally, rise again to 1,200 milligrams for people 51 and over.

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