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No link found between 25-hydroxyvitamin D and breast cancer

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ASCO Breast Cancer Symposium

WASHINGTON — The results of the Women’s Health Initiative study involving more than 36,000 postmenopausal women suggest that 25-hydroxyvitamin D has no preventative effect on breast cancer.

Rowan T. Chlebowski, MD, PhD, chief of medical oncology/hematology with the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, Calif., presented the results at the 2008 ASCO Breast Cancer Symposium.

The researchers randomly assigned 36,282 healthy postmenopausal women to placebo or 1,000 mg daily calcium and 400 IU daily vitamin D. The researchers found a strong correlation between vitamin D levels and BMI and physical activity (P<.0001), which are recognized breast cancer risks. However, they found no association between vitamin D levels and breast cancer risk after adjusting for BMI and physical activity (P=.20). Chlebowski said that held true no matter the level of vitamin D in the blood.

“There is no association between 25-hydroxyvitamin D levels in the blood and breast cancer,” he told HemOnc Today. “The most interesting finding is that the levels of 25-hydroxyvitamin D — which some people have said you have to target to get the levels up — we found that the levels were already up even though only 3% of women were taking a high supplement dose. It suggests other factors determine that level.”

These findings contradict the results of earlier studies that suggested 25-hydroxyvitamin D could prevent breast cancer in some women.

“The reason we don’t show association and other people might is that they probably don’t control for as many factors apparently related to vitamin D levels that are also related to breast cancer risk,” Chlebowski said. “There aren’t any data to suggest that if you give supplementation to target a certain level you’re going to reduce breast cancer risk. This is strong evidence against that association.” – by Jason Harris

Is 400 IU enough in a postmenopausal population? Probably not, but that was the official recommendation when they started the study, so one can't fault them for that. This study doesn't conclusively prove an association between a low vitamin D level and a risk for getting breast cancer, but it certainly doesn't disprove it either. I would not view this as being conclusive. The study's ability to detect an association is limited, and these results don't mean this is a dead question. There are biologic possibilities here that I think are worthy of prospective studies.

– Julie Gralow, MD

Director of Breast Medical Oncology
University of Washington and Fred Hutchinson Cancer Research Center

For more information:

• Chlebowski RT, Johnson KC, Kooperberg C, et al. #3. Calcium plus vitamin D supplement use, 25-hydroxyvitamin D (25 OHD) levels and breast cancer risk in the Women's Health Initiative. Presented at: 2008 ASCO Breast Cancer Symposium; Sept. 5-7, 2008; Washington.