Milk for Your Bones?
Is Milk Best?
Reviewed By Michael Smith
Oct. 6, 2000 -- Growing up, milk was non-negotiable in our house. Like a team of star athletes with a dairy council sponsorship, my family of six guzzled gallons of the stuff. Nearly every night before dinner my mother pressed $2 into my hand. Off I went to the corner store to replace the jug my brother had polished off with his after-school snack.
When I left for college, my mother's mantra, "milk makes healthy bones," played in my head as I sidled up to the steel-gray 50-gallon tank in the cafeteria and filled a 16-ounce glass with every meal. After all, osteoporosis had confined my shrunken grandmother to bed -- the bones of her spine slowly dissolving into dust. Who was I to question my mother's wisdom?
Like most women, my mother got her information from doctors and health organizations who for years have touted milk as the key to healthy bones. But is dairy really the best source of calcium? The question stirs emotions on both sides of the debate. Dairy supporters revere milk as the perfect vehicle to transport calcium to bones. Those opposed argue that, among other things, proteins found in dairy products actually rob calcium from bone stores, making plant-based sources -- and exercise -- a better choice for healthy bones.
As a vegetarian, I'm frustrated by the mixed messages surrounding the question of dairy as the best source of calcium. In my quest to avoid sharing my grandmother's fate, I've discovered that the issue is more about educating myself to make informed decisions than blindly swallowing anyone's advice -- even Mom's. There's much more to the story than Mom knew.
Milk: Does It Really Do a Body Good?
It turns out that the relationship between the proteins in dairy products and the calcium in bones is a rocky one. First of all, calcium appears to be ultimately pulled from bones to escort digested animal protein from any source -- not just dairy products -- on its trek through the body. Since the average American's diet is protein-heavy to begin with, some experts say that eating lots of dairy foods may actually cause people to lose calcium. "When you eat a protein food, such as milk, you may be swallowing calcium, but you turn around and excrete calcium in your urine," says Donna Herlock, MD, spokeswoman for the Physicians Committee for Responsible Medicine, a nonprofit advocacy group opposed to milk consumption.
To buttress her point, Herlock points to a portion of the Harvard Nurses' Health study published in the June 1997 issue of the American Journal of Public Health. The study found that women who ate lots of dairy products had higher rates of bone fractures than women who rarely touched the stuff. It suggested that drinking more milk didn't provide any substantial protection against hip or forearm fractures in middle-aged and older women, writes Diane Feskanich, ScD, a professor at Harvard Medical School in Cambridge, Mass., and the study's lead author. "We considered the possibility that dairy protein was responsible for the increase in risk of hip fractures," she says.
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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.
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.
No Bones About It
Clearly, there is consensus that calcium is necessary for good health -- but no consensus on whether calcium is best when consumed from dairy or other sources. My own decision has been to get my calcium fix in a variety of ways. I still treat myself to a slice of cheese pizza now and again, but I also pour calcium-enriched soy milk on my cereal, drink calcium-fortified orange juice, and load up on dark leafy greens.
When I told my mother I'd cut back on my milk consumption, I might as well have announced that I'd given up oxygen. But she's slowly gotten used to the idea. Now when I visit, instead of slipping me money to buy milk, she opens her denim purse, digs down deep, and hands over a bite-sized, foil-wrapped piece of chocolate -- calcium-enriched, of course.
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