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Vitamin D May Help Block Breast Cancer

Vitamin D could play a role in helping to prevent breast cancer, according to a California researcher.

Esther John of the Northern California Cancer Center in Union City compared dietary and sun exposure data among 133 women diagnosed with breast cancer to a group who did not have the disease. She found that those who had the most sun exposure - a major source of vitamin D - or who received 200 international units of the vitamin daily had a reduced risk of breast cancer, after accounting for all the known risk factors for breast cancer.

John presented her results Saturday at the Era of Hope breast cancer research conference sponsored by the Department of Defense. She cautioned that the results were preliminary and the study was small. In fact, because of that, the reductions seen - about 30 to 40 percent - were not statistically significant.

Nevertheless, John said she was excited by the findings. “We really feel the data suggests something that could be helpful and we need more studies.” She said it was the first study looking at a possible role of vitamin D and breast cancer.

Lab studies have found that a metabolite of vitamin D, 1,25 dehydroxy-vitamin D, can slow down the growth of healthy cells and breast cancer cells. Moreover, those who live in the South have a lower mortality from breast cancer compared to women in northern climes. The two prompted John to try to look at sun exposure and dietary intake.

Using government data, John found that those women who had lived longest in areas with the most sun exposure or who were rated as having moderate to frequent exposure to the sun had the lowest risk of breast cancer.

The role of vitamin D from the diet was less clear. Those women who got 50-99 International Units, or IUs, of vitamin D a day had a 21-percent reduction in the risk of breast cancer compared to those who got less than 50 IUs a day; those who got 200 IUs a day - the recommended daily allowance - had a 33-percent reduction. But those who got 100-199 IUs a day showed no reduction, a finding John could not explain.

She also cautioned that these results should not prompt women to spend a long time in the sun; sun exposure is related to an increased risk of skin cancer. “In order to have adequate vitamin D synthesis,you need to be out in the sun about 10 to 15 minutes a day and eat a healthy diet,” she said.