Los Angeles Times
March 7, 2005

The dairy debate: Does milk build stronger bones?
Some scientists are questioning dairy products' effectiveness in
helping prevent osteoporosis.
By 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.

Americans have weak bones not because they drink too little milk but
because they drink too much, Campbell says. Animal protein, such as the
protein in milk, makes blood and tissues more acidic, and to neutralize
this acid, the body pulls calcium, which is a very effective base, from
the bones. Because dairy products contain substantial amounts of animal
protein, drinking milk actually robs the bones of calcium, he says. The
more meat and milk Americans eat, he says, the more calcium they need
to consume to process that protein.

That's ridiculous, osteoporosis researchers say. Although they agree
that eating excessive amounts of protein may leach calcium from the
bones, they see moderate amounts of protein-rich dairy foods as an
excellent way to keep bones strong.

"There is a growing number of studies that have shown an association
between higher protein intake and less bone loss," says Bess
Dawson-Hughes, director of the Bone Metabolism Laboratory at Tufts
University.

To be sure, many studies do point to a connection between dairy and
bone health.

A research review of 138 studies exploring the relationship between
bone health and calcium intake, including numerous studies that used
dairy products as the calcium source, found overwhelming evidence that
lifelong calcium intake is one of the most significant factors for
determining risk of an osteoporotic fracture, says Deanna Segrave-Daly,
a registered dietitian and spokeswoman for the National Dairy Council.

The review was published in the American Journal of Clinical Nutrition
in 2000.

But that same review reported that not all dairy foods boost bone
health. "Foods such as milk and yogurt are likely to be beneficial;
others, such as cottage cheese, may adversely affect bone health," the
review states. "The high calcium content of processed cheese products
may be offset by the high sodium, polyphosphate, and protein contents
of these products, which can be expected to increase calcium losses."

Researchers say there are several possible reasons why milk study
results vary so.

Most clinical trials - studies in which one group of people increases
calcium intake and another group does not - have shown that adding
calcium to the diet increases bone density. But most clinical trials
last for less than three years, says Diane Feskanich, an investigator
for the Nurses' Health Study. "It could be that bone density does not
continue to increase in the long run - in fact, a study that went on
for three years found that after an initial increase in bone density,
it did not continue to increase in the third year."

Observational studies such as the Nurses' Health Study "are usually run
over many years and in this way better suited to determine the
long-term effects of high calcium intakes," Feskanich says.

It is also possible that vitamin D is as important or more important
than calcium for maintaining bone density into adulthood.

Researchers don't understand exactly what role vitamin D plays, but
there is a growing belief in the scientific community that the poor
state of the nation's bones has something to do with a widespread
shortage of vitamin D. The body gets vitamin D from food and sunlight,
and as people cover up to avoid the cancer-causing rays of the sun,
they may also send vitamin D levels plummeting. "Most Americans are
short on vitamin D," Willett says.

The rest of the diet may play a part in bone health too, in ways
researchers don't yet understand. Other nutrients in the diet may
either help or hinder calcium absorption. "We are overfed, but are we
eating the right things?" asks Lori Hoolihan, nutrition research
specialist with the Dairy Council of California. "We are a fat nation,
but in some ways we are malnourished."

Even those researchers who agree with the three-glasses-a-day
recommendation say there is a limit to what dairy calcium can do. "The
gene pool accounts for most of your risk," Dawson-Hughes says.

During the years in which people build bone mass - from birth to
about age 20 or 25 - bone density is determined 80% by genetics and
only 20% by lifestyle factors such as exercise and diet. Bone loss,
which starts to occur after age 25 or so, is determined half by
genetics and half by lifestyle choices, Dawson-Hughes says.

Finally, there is an emotional side to this issue. The dairy debate is
conducted in large part by two groups who accuse each other of twisting
science and letting money or ideology cloud their views: the dairy
industry and vegetarians.

The dairy industry accuses the anti-dairy camp of promoting an
animal-free diet whether it makes nutritional sense or not. Dairy
critics charge the dairy industry with bankrolling pro-dairy research
and influencing the government's dietary recommendations.

One thing both parties agree on is that exercise helps to build bones
and maintain bone density throughout life.