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Higher vitamin D may help prevent breast cancer
Harvard
Women's Health Watch
We've known for a long time that vitamin D is crucial to
bone health. Research is now showing that it's active in
many other tissues and may offer some protection against a
range of diseases, including certain cancers. To get this
benefit, though, we likely need more than the current
recommended amounts.
At the American Association for Cancer Research meeting in
April 2006, researchers offered compelling evidence that
boosting vitamin D intake could help reduce the risk of
breast cancer. In a study of 1,760 women, California
scientists found that risk fell steadily with increasing
blood levels of vitamin D. The highest levels (more than
52 nanograms per milliliter, or ng/mL) correlated with a
50% reduced risk of breast cancer, compared with the
lowest amounts (less than 12 ng/mL). To reach a blood
level of 52 ng/mL, you would need several times the
recommended intake, which is 400 international units (IU)
of vitamin D per day for women ages 50-70.
A second study, by Canadian researchers, found that women
who spent more time outdoors or got more dietary vitamin D
in their teens and early adulthood were 25%-45% less
likely to develop breast cancer.
Although not yet peer-reviewed, the data are consistent
with mounting evidence that increased vitamin D helps
prevent many types of cancer, including breast, ovarian,
colon, and prostate cancers.
Tough to get enough Vitamin D is a hormone whose
manufacture begins in the skin with exposure to the sun's
ultraviolet B rays. With enough sun, we wouldn't need
dietary vitamin D. But dependence on the sun is a problem.
Skin cancer is one worry. Sunscreens help with that
concern, but they also block the rays that spur vitamin D
synthesis in the skin. Moreover, people who live above 40
degrees north latitude - in Boston, for example - can't
make enough vitamin D from sunlight in the winter.
Other factors influence the amount of vitamin D you can
make from sunlight. The darker your skin, the more sun
exposure it needs. And as we age, our skin becomes less
capable of triggering vitamin D synthesis.
Natural food sources of vitamin D - primarily fatty fish
such as salmon and mackerel - are limited. Fortified foods
(milk and some breakfast cereals) supply modest amounts.
What to do Nutrition experts have already begun to
recommend that adults get 800-1,000 IU of vitamin D per
day. A standard multivitamin usually supplies 400 IU; you
can get an extra 400 IU in a vitamin D supplement. Calcium
tablets often contain vitamin D, so include them in your
calculations. Don't overdo it; excessive vitamin D, which
usually results from overdosing on supplements, can cause
a buildup of calcium in tissues. The tolerable upper limit
is still 2,000 IU per day.
The most active form of vitamin D is D3 (cholecalciferol),
the type produced in the body. Most supplements contain
D2, which is made from plant material. Some experts say
that D3 is more effective. (It's also more expensive and
harder to find.)
Don't take cod liver oil. It contains large amounts of
vitamin A as retinol, which at high levels can be harmful
to bones.
You
can usually get adequate vitamin D from 10 to 15 minutes of
sun a couple times a week, without sunscreen, on the face,
arms, and hands. Many health experts see little harm in this
level of exposure. For longer periods in the sun, use
sunscreen.
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