Supplements don't reduce breast cancer risk

NEW YORK, 15 nov 2008– Calcium or vitamin D supplements do not reduce the risk of invasive breast cancer in postmenopausal women, according to a report in the Journal of the National Cancer Institute.

The findings of observational studies have linked higher calcium and vitamin D levels with a lower risk of breast cancer, but until now this topic had not been addressed in a different type of 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 randomly assigned to receive calcium 1000 milligrams plus vitamin D 400 IU daily or placebo for 7 years, on average, to determine the effect of these supplements on hip fractures. The supplements' effect on invasive breast cancer was a secondary endpoint of the study. Mammography and breast exams were performed regularly during the follow-up period.

The number of patients who developed invasive breast cancer in the supplement group was not significantly different from the number in the placebo group: 528 versus 546.

The researchers analyzed initial levels of 25-hydroxyvitamin D levels in 1,067 women who developed breast cancer and in 1,067 who did not, to examine the impact of 25-hydroxyvitamin D levels, the most accurate measure of vitamin D levels in the body.

Among the women who developed invasive breast cancer, 25-hydroxyvitamin D levels were similar in the nutrient and the control group. After adjusting the data for variations in weight and physical activity levels, the authors found no correlation between 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 issues they have 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 potential factors, noted by the editorialists, include the vitamin D levels at study entry and the fact that patients in the control group were permitted to take a relatively high amount of calcium and vitamin D outside of study.

SOURCE: Journal of the National Cancer Institute, online November 11, 2008.