Calcium and vitamin D use does not prevent invasive breast cancer

NEW YORK (Reuters Health) - Use of calcium and vitamin D supplements does not reduce the risk of invasive breast cancer in postmenopausal women, according to a report in the November 11th online issue of the Journal of the National Cancer Institute.

Findings from observational studies have linked higher calcium and vitamin D intake with a lower risk of breast cancer, but until now this topic had not been addressed in a randomized trial, lead author Dr. Rowan T. Chlebowski, from the University of California, Los Angeles, and colleagues note.

In the Women's Health Initiative study, 36,282 participants were randomized to receive calcium 1000 mg plus vitamin D 400 IU daily or placebo for 7 years, on average, to determine the effect on hip fractures. Invasive breast cancer was a secondary endpoint, and mammography and breast exams were performed regularly during follow-up.

The number of patients who developed invasive breast cancer in the supplement group was not significantly different from the number in the control group: 528 vs. 546 (HR = 0.96).

In a nested case-control analysis of 1067 patients who developed breast cancer and 1067 who did not, the researchers examined the impact of baseline 25-hydroxyvitamin D levels on breast cancer risk.

Among the women who developed invasive breast cancer, the mean 25-hydroxyvitamin D level was 50 nmol/L compared with 52 nmol/L in the control group. After adjusting for body mass index and physical activity, the authors found no correlation between baseline 25-hydroxyvitamin D levels and breast cancer risk.

In a related editorial, Dr. Corey Speers and Dr. Powel Brown, from Baylor College of Medicine in Houston, list some methodologic issues with the current study and conclude that "the potential health benefits of vitamin D and calcium may yet still have a bright future."

Two key confounders, noted by the editorialists, include the "variable baseline vitamin D levels" and that patients in the control group were permitted to take a relatively high amount of calcium and vitamin D "outside of study" supplementation.

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