Got Osteoporosis?

articles
Aug. 3 1999 3:30 AM

Got Osteoporosis?

Maybe all that milk you've been drinking is to blame.

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It will be hard to frolic through the next millennium with bones that have turned to sawdust. That is the fate that awaits those of us, we are told, who don't consume the escalating amount of calcium--now at a quart of milk a day or the equivalent--endorsed by public health officials. Just two years ago the National Academy of Sciences increased its daily recommendation for calcium by 50 percent for older Americans. Another upward revision and we will all have to be attached to udders with an IV. Strange, then, that most of the world's people, who rarely if ever drink milk and who get just a small percentage of the calcium we are told is vital, have not devolved into boneless heaps of protoplasm. Even stranger, in many of these dairy-avoiding countries, people get through life with far fewer of the age-related hip fractures that plague Americans.

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This paradox has led a small number of researchers to become dairy doubters, questioning the wisdom of the calcium recommendations of the public health establishment. For one thing, the doubters say, our diet is so fundamentally flawed that trying to protect our bones by taking in loads of calcium is like trying to fill a tub with no stopper by turning up the faucets. The problem is this: In general, world dietary patterns show that countries where people consume large amounts of calcium are also countries where people eat extravagant amounts of animal protein, places such as the United States and northern Europe. These countries also suffer among the world's highest rate of fractures due to osteoporosis, the disease characterized by weak, porous bones. "The correlation between animal protein [intake] and fracture rates in different societies is as strong as that between lung cancer and smoking," says T. Colin Campbell, professor of nutritional biochemistry at Cornell University.

Our bodies contain 2 pounds to 4 pounds of calcium, 99 percent of which is in our bones and teeth, the rest circulates in the blood where it is necessary for nervous-system function. Eating animal protein, which is high in sulfur-containing amino acids, requires the body to buffer the effects of those amino acids. It does so by releasing calcium from the bones, literally peeing them away. But this leaching of calcium should be offset if the balance of calcium to protein in the diet is within a reasonable range. Robert Heaney, professor of medicine at the Creighton University School of Medicine and a proponent of high dairy consumption, found in a study he co-authored that the "single most important determinate of the rate of bone gain" in young women was not the amount of calcium consumed but the ratio of calcium to protein. But it's a difficult balance to strike when it's common for Americans to eat double the protein we need, with 70 percent of it coming from animal sources.

Could there be some other dietary factor at work as well? Retired Harvard professor of nutrition Mark Hegsted thinks there may be. He believes calcium consumption may be at the root of our bone problems, but his heretical hypothesis is not that we don't get enough calcium but rather that we get too much. In an article in the Journal of Nutrition he writes, "[H]ip fractures are more frequent in populations where dairy products are commonly consumed and calcium intakes are relatively high. Is there any possibility that this is a causal relationship?"

Hegsted explains the way such a mechanism would work. The body adapts to low calcium intake by efficiently using what is available. Conversely, high calcium consumption causes the body to decrease the amount of the mineral that is absorbed, excreting the excess. That's why populations with low calcium consumption manage to form healthy skeletons, and high calcium consumers don't develop bones like mastodons. But what happens over time, Hegsted suggests, is that the inefficient consumers may permanently damage their abilities to effectively use dietary calcium and to conserve calcium in the bones later in life. As we age, the body naturally goes from building bone to losing it. Hegsted's hypothesis explains why high dairy consumers so often end up with rampant bone loss. He cites studies of rural Gambian women who don't drink milk, get about one-quarter of the calcium we're told to consume, yet rarely have osteoporotic fractures. "It will be embarrassing enough if the current calcium hype is simply useless; it will be immeasurably worse if the recommendations are actually detrimental to health," he writes.

Emily Yoffe Emily Yoffe

Emily Yoffe is a regular Slate contributor. She writes the Dear Prudence column. 

Cornell's Campbell says our fate could be different if we would take a lesson from the Chinese (fortunately he's a nutritionist, not a political scientist). He has spent the last 20 years studying the health and dietary habits of rural Chinese and comparing them to those in the West. These Chinese consume less than half the calcium we're told is necessary, virtually all of it from plant sources, in particular leafy green vegetables. They have one-fifth the incidence of hip fracture of Americans. Although they consume more calories per day than we do, only about 10 percent of their diet is from animal sources. On average, American diets are 70 percent animal-based.

Campbell has what could be called the unified field theory of bones and breasts. He explains the mortal consequences of diets high in dairy, protein, and fat. Early in life, American girls consume lots of these, which leads to relatively dense bones, high levels of estrogen, and early sexual maturation. The age of menarche has been dropping for decades in this country and now often occurs as early as age 10. In rural China, girls don't usually begin menstruation until age 15. Chinese women have only about two-thirds of the amount of circulating estrogen that American women do, which helps account for their far lower rate of breast cancer, says Campbell.

Estrogen helps maintain bone, so most women's skeletons are fine until menopause. Then estrogen levels drop, in the case of American women faster and lower than their Chinese counterparts. "Now they're vulnerable," says Campbell. "That all suggests that the factors that cause osteoporosis are rather similar to the ones that cause breast cancer."

Two very different sets of studies support his theory. One compares bone density of Japanese and British women. The Japanese get almost all their calcium from soy, the bones of small cooked fish, and vegetables. They also have about 40 percent the rate of hip fracture of the West. The British diet is similar to ours and so is their hip fracture rate. Before menopause, the British women do indeed have denser bones than the Japanese. But following menopause, the British women end up losing more bone than the Japanese. And a spate of recent studies in this country has found that women with the highest measured bone density, a much-desired goal according to the literature on osteoporosis, have a significantly increased incidence of breast cancer.

Campbell says views such as his are not more widely known because, "Unfortunately, we are absolutely drowned in information coming out of the dairy industry. ... Our national nutrition policies are corrupted by the influence of the dairy industry."

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