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Does vitamin D reduce the risk of cancer?
Boston Globe
By Judy Foreman | August 7, 2006

Several recent studies presented at meetings of the American Association for Cancer Research and the American Society of Clinical Oncology suggest that adequate consumption of vitamin D -- which most Americans do not get -- is linked to lower risks of breast cancer.

One study, from researchers at the University of California, San Diego, looked at pooled data on 1,760 women and found that the highest level of vitamin D consumption was correlated with a 50 percent lower risk of breast cancer. To achieve this level of vitamin D, a person would have to consume at least 1,000 International Units of vitamin D a day, well beyond the current recommended levels of 200 IUs a day for children and adults up to age 50 (the figure rises for people over 50).

In another study, researchers at Mount Sinai Hospital in Toronto interviewed 576 patients with breast cancer and 1,135 people without and found that those who had frequent sun exposure as teenagers or young adults had a 35 to 40 percent reduced risk of breast cancer. (Sunlight helps the skin produce vitamin D.)

On the other hand, a study that was part of the government-sponsored Women's Health Initiative found that calcium and vitamin D supplements did not reduce breast cancer risk in post-menopausal women -- though when women randomized to get the supplements did get breast cancer, their tumors were smaller than those of women not taking supplements.

Dr. Michael F. Holick , a vitamin D expert and professor of medicine, physiology, and biophysics at Boston University Medical Center, said that other studies suggest that vitamin D may also help prevent colon, ovarian, and prostate cancer.

People can get vitamin D by ``sensible" sun exposure (5 to 10 minutes several times a week without sunscreen), supplements, and a diet rich in fortified cereals, milk, and oily fish. Holick recommends at least 1,000 international units of vitamin D a day, preferably the strong form, called D3, not D2, the kind that is in most supplements.

``While these studies certainly suggest that getting adequate vitamin D is important," said Dr. Kala Visvanathan , a cancer specialist and epidemiologist at the Johns Hopkins Bloomberg School of Public Health, ``it is not clear that taking extra is beneficial or whether dose should be altered, depending on age."

Vitamin D in very high doses can be toxic. The Institute of Medicine is expected to decide within several years whether to recommend increased intake of vitamin D. Currently, the institute sets the upper limit for consumption at 2,000 IUs a day.

JUDY FOREMAN

E-mail health questions to Foreman@globe.com.