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Science
not clear on milk,
health link
March 17, 2005
It’s
important to examine widely believed notions about nutrition.
Sometimes, conventional wisdom doesn’t bear up to close
scrutiny.
For example, for generations people believed they should drink
eight glasses of water per day, though there was never any
science to back the recommendation. We know now to let thirst
be our guide.
Likewise, there is a widely held belief that milk is necessary
for health. While it’s clear that calcium and other
nutrients found in milk are necessary, the science is not
clear that drinking more milk is good for most people.
But the idea is deeply embedded in our dietary and agricultural
practices –reinforced by widespread advertising by the
dairy industry.
In fact, the 2005
Dietary Guidelines for Americans raised recommendations
for milk consumption from two servings in previous reports
to three servings for most Americans. The primary reason cited
in the report is the claim that milk promotes bone health.
But some nutrition experts question the rationale.
First, let’s consider the recommendations for calcium
intake.
The government’s calcium recommendations are based on
the National Academy of Science’s analysis of “balance
studies” that measure the point at which the amount
of calcium consumed equals the amount the body excretes. Those
studies suggest an adequate intake is 550 milligrams a day.
But the government’s recommendations were set by the
NAS at about double that level for most people – at
1,000 or 1,200 milligrams a day – to ensure that 95
percent of the population reaches the 550-milligram intake
level. Government recommendations that we consume three servings
of dairy products each day are geared toward reaching the
elevated 1,000-milligram calcium intake level.
Researchers at the Harvard School of Public Health, writing
in their online nutrition guide Nutrition
Source, question this approach because:
* Balance studies are short-term. Long-term studies give a
more accurate picture of how the body may adapt to varying
calcium intakes over time. Long-term studies, including some
by Harvard researchers, suggest high doses of calcium from
milk don’t lower osteoporosis risk.
* Others do fine with less. In India, Japan and Peru, people
getting 300 milligrams of calcium each day on average have
low rates of bone fracture. It’s possible that factors
such as more physical activity or more vitamin D from sunlight
account for the difference.
* Others come to different conclusions. The British government
used the same research and arrived at recommendations for
calcium that are about one third lower than those in the U.S.
Other points to consider:
* Dairy products are the leading source in the American diet
of artery-clogging saturated fat.
* Cow’s milk is only one of many sources of calcium.
Others include dried beans, greens, some fruits, and fortified
foods such as fruit juices, breakfast cereals and soymilk.
* Cheese and milk are high in sodium and devoid of fiber.
* Lactose intolerance affects the majority of blacks, Asians,
Hispanics and Native Americans. It’s a natural condition
after infancy when the body no longer needs the enzyme that
breaks down the sugar in milk. Symptoms include gas, bloating,
cramps, and diarrhea.
* Some studies suggest high intakes of dairy products may
be associated with increased risk of ovarian cancer, and high
intakes of calcium may also increase the risk of prostate
cancer.
Harvard’s conclusion: “Currently, there’s
no good evidence that consuming more than one serving of milk
per day in addition to a reasonable diet (which typically
provides about 300 milligrams of calcium per day from nondairy
sources) will reduce fracture risk. Because of unresolved
concerns about the risk of ovarian and prostate cancer, it
may be prudent to avoid higher intakes of dairy products.”
That’s not the message you’ll see in the popular
media, but suggestions that we drink and eat more dairy products
need closer scrutiny.
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