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The dairy debate: Does milk build stronger bones?

Some scientists are questioning dairy products' effectiveness in helping prevent osteoporosis.

March 07, 2005|Alice Lesch Kelly | Special to The Times

Bones need calcium. Doctors, dietitians and researchers agree on this point.

Conventional wisdom holds that dairy foods are the best source of calcium, and that American adults need to pump up their dairy intake to get the large amount of calcium their bodies need every day. Not everyone, however, believes the conventional wisdom.

Researchers are even raising questions about whether children need as much milk as guidelines recommend. A review article in the current issue of the journal Pediatrics concludes that there is "scant evidence" that increasing dairy intake is the right way to promote bone health in children.

Lately a small but highly respected band of scientists has been speaking out. They say Americans need less calcium than dietary guidelines recommend, and that drinking cup after cup of milk is not the best way to get it.

On one side are the federal government, the dairy industry and the majority of the nutrition community.

Milk plays a big part in the dietary guidelines recently released by the federal government. Anyone older than 8 is urged to drink three cups of low-fat or fat-free milk or eat an equivalent amount of yogurt or cheese each day. The thinking behind this recommendation is that the calcium in dairy products helps build strong bones and wards off osteoporosis, a disease in which bones become porous and break easily.

On the other side are nutrition researchers from Harvard and Cornell universities who say that when it comes to dairy, the U.S. dietary guidelines have gone too far. They believe that exercise, heredity, hormone levels, smoking, protein intake and intake of vitamins D and K matter more than milk.

The debate over dietary calcium is occurring because of rising concern over osteoporosis, or low bone mass. An estimated 10 million Americans older than 50 -- most of them women -- have osteoporosis, and 34 million are at risk for developing it.

By 2020, one in two Americans older than 50 will be at risk for fractures from osteoporosis or low bone mass, according to the U.S. Surgeon General, who issued a report in October that sounded an alarm on bone health. Bone health is so important that President Bush has declared 2002-11 as the "decade of the bone and joint."

As for the link between dairy products and osteoporosis, "there's no solid evidence that merely increasing the amount of milk in your diet will protect you from breaking a hip or wrist or crushing a backbone in later years," says Walter C. Willett, chairman of the Department of Nutrition at the Harvard School of Public Health.

Willett bases his calcium conclusions on research that he and his team at Harvard have done during the last 25 years. He is one of the principal investigators of the Nurses' Health Study, which has looked at the diet and health of tens of thousands of nurses since 1980, and of the Health Professionals Follow-Up Study, an all-male study underway since 1986.

When Willett and his colleagues investigated the milk-drinking habits of 72,000 women in the Nurses' Health Study, they found that milk consumption was not associated with a lower risk of hip fracture, a measure of bone strength. In fact, women who drank milk twice a day were as likely to suffer a bone break as women who drank it once a week.

Likewise, the Health Professionals Follow-Up Study failed to find a relationship between calcium intake and bone fractures in more than 43,000 men. And a 2003 Swedish study of more than 60,000 women, which was published in the journal Bone, found no association between dietary calcium intake and fracture risk.

"We do need some calcium -- it's essential -- but the question is, how much?" says Willett, author of the 2001 book "Eat, Drink, and Be Healthy." He believes the body needs 500 to 700 milligrams of calcium daily rather than the 1,000 to 1,500 milligrams a day recommended by the dietary guidelines.

T. Colin Campbell, professor emeritus of nutritional biochemistry at Cornell University, also questions dairy's place in the dietary guidelines. "I like dairy. I grew up on a farm. But one has to look at the facts," he says. "Dairy has been considered a health food, and that's an unfortunate myth."

Campbell's views come from observations he and his colleagues made during a series of nutritional studies that began in 1983 and are collectively known as the China Study. In these studies, Campbell found that Asians, who consume far less dietary calcium than Americans, have one-fifth the bone fracture rate of Americans.

"Those countries that use the most cow's milk and its products also have the highest fracture rates and the worst bone health," Campbell says. He details the results of his work in a new book called "The China Study."

In Asian countries, people can get all the calcium their bodies need from plant sources such as leafy green vegetables, Campbell says.

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