Milk for Your Bones?
Is Milk Best?
Milk: Does It Really Do a Body Good? continued...
Milk advocates pooh-pooh the protein concern. The amount of calcium lost in the urine from drinking a glass of milk is trivial compared with the amount of calcium coming in, says Connie Weaver, PhD, head of foods and nutrition at Purdue University in West Lafayette, Ind. "For every gram of protein you eat, you lose 1.75 milligrams of calcium." Using this calculation, since each glass of milk provides 8 grams of protein, you'll lose 14 out of 300 milligrams of calcium per glass -- which doesn't seem so bad. In fact, because the average American consumes approximately 75 grams of animal protein a day (though of course not all from milk), you'll still take in more calcium than you lose by drinking just one glass of milk (you'll consume 300 milligrams of calcium and only lose 131 milligrams).
Robert Heaney, MD, a professor of medicine at Creighton University in Omaha, Neb., who specializes in bone biology, also shrugs off dairy dissenters. "The reason why dairy products work is that they contain not only calcium and protein but also phosphorus, magnesium, vitamin D, potassium, and other things associated with good bone health," he says. "It's the logical way to go."
The Wonders of Workouts
My mother, clearly pro-dairy, consumes lots of calcium and is determined to fight osteoporosis head-on. For a woman about to turn 60, her bones are in great shape. But according to one recent study that dairy doubters add to their arsenal, she has more than milk to thank for that bragging right.
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.