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April 24, 2013
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Jewish World Review
Do we really need all that calcium?
By
Harvard Health Letters
JewishWorldReview.com |
Recent studies suggest that there's been too much focus on calcium for
bone health and fracture prevention.
Calcium serves many functions in the body, but the main one is to form
the structures that give our bones and teeth their strength and shape.
As we get older, the mineral content (there's some phosphorus in there
as well) of our skeleton declines. Our bones start to thin out bit by
bit, so they become less dense, more brittle, and more likely to
break. When this thinning advances to a certain point, it's called
osteoporosis. Each year in the United States there are 1.5 million
bone fractures associated with osteoporosis, and 250,000 of those
breaks will involve a hip.
NEGATIVE RESULTS
For years, high calcium intake has been portrayed as one of the best
things you could do to prevent osteoporosis and related fractures.
Research results supported this view, although many of the studies
were fairly small and short.
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But when researchers started to crunch the data from large,
prospective studies that followed people for many years, the benefits
weren't so clear-cut. The ambiguity led to randomized trials of
calcium to test what effect it might have on fracture rates.
The tide started to turn in 2005 when results from two British studies
showed that calcium didn't prevent fractures -- even when taken in
combination with vitamin D. The next year, results from a large
American trial, the Women's Health Initiative, showed that
postmenopausal women who took a calcium-vitamin D combination were no
less likely to break their hip than women who took a placebo pill,
although the density of their hip bones increased slightly. In 2007, a
Swiss and American team, including some researchers from Harvard,
reported the results of a meta-analysis of over a dozen studies of
calcium. They found no connection between high calcium intake, from
either food or pills, and lower hip fracture risk. In fact, when they
limited their analysis to four randomized clinical trials with
separate results for hip fractures, they found that extra calcium
increased the risk.
THE WHYS AND WHEREFORES
While a certain level of calcium intake is undoubtedly important to
keeping bones strong, amounts above that level might not do much good.
One reason extra calcium didn't show any benefit in the Women's Health
Initiative may have been because the women in that study were, on
average, already getting over 1,000 milligrams (mg) daily. And they
weren't all that unusual. Because of dairy products and calcium pills,
many Americans are amply supplied with calcium.
Another theory: calcium in large amounts may interfere with absorption
of phosphorus, which is also crucial to maintaining bone strength.
Phosphorus deficiency isn't a major problem in well-fed populations,
but it's possible that extra calcium pushes some people into it,
especially if their diets don't include much protein.
Another factor may be that added calcium isn't all that beneficial if
our vitamin D intake is low. The body needs vitamin D to absorb
calcium, and depending on how you define it, between 30 percent and 60
percent of us have less-than-optimal levels of vitamin D in our blood.
SO NOW WHAT?
According to current recommendations, Americans over 50 are supposed
to get 1,200 mg of calcium daily. Dr. Walter C. Willett, chair of the
Harvard School of Public Health's nutrition department, believes that
many Americans are getting more calcium than they need. In his
opinion, 600 mg is probably enough for most people to keep their
fracture risk low, but because extra calcium might be protective
against colon cancer, he sees a daily intake of 600 to 1,000 mg as a
reasonable goal. There may be real drawbacks to overdoing calcium,
especially if dairy foods are the source. Dr. Willett points to
studies linking high consumption of dairy products to ovarian and
prostate cancer, noting that the relationship seems particularly
strong for metastatic and fatal prostate cancer.
Current guidelines say Americans in the 50-plus age bracket are
supposed to get 400 to 600 international units (IU) of vitamin D. But
a growing number of experts -- including Dr. Willett -- say that's not
enough, and that 800 IU, or even 1,000, would not only benefit our
bones but possibly prevent some cancers and other problems.
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