Posted on March 8th, 2009 by
Calcium and vitamin D supplementation may not reduce the risk of breast cancer, according to the results of a study recently published in an early online version of the November 2008 issue of the Journal of the National Cancer Institute.
The role diet plays in relationship to cancer risk has long been a focus of researchers. Evidence continues to mount indicating that diet may drastically reduce the risk of developing certain types of cancer. Research is ongoing to evaluate specific nutrients and the difference between obtaining them through diet or through supplementation. The most recent shining star has been vitamin D, which is a fat-soluble vitamin that comes from dietary supplements, foods such as fortified milk and cereal, certain kinds of fish (including salmon, mackerel, and tuna), and exposure to sunlight.
Vitamin D has been shown to reduce the risk of colorectal polyps. In addition, low levels of circulating vitamin D have been linked to worse outcomes for breast cancer patients. However, results have been inconsistent among other studies. While some studies seem to show a reduction in breast cancer incidence with increased vitamin D intake, others show no association. As a result researchers are continuing to study vitamin D in order to determine just what its protective benefits are, if any.
In this recent study, 36,282 postmenopausal women who were enrolled in the Women’s Health Initiative (WHI) clinical trial were randomly assigned to receive daily supplementation with 1000 mg of calcium and 400 IU of vitamin D or placebo. These women were then followed for seven years. The primary endpoint of the study was to determine the impact of the supplementation on the incidence of hip fracture; however, a secondary endpoint was invasive breast cancer.
The results indicated that the incidence of invasive breast cancer was similar between the two groups, with 528 cases in the supplementation group versus 546 in the placebo group, leading the researchers to conclude that calcium and vitamin D supplementation did not reduce the incidence of invasive breast cancer in postmenopausal women. Interestingly, the researchers also measured circulating levels of vitamin D and higher levels were strongly associated with leanness and high physical activity, which both influence breast cancer risk. This led the researchers to speculate that prior studies linking vitamin D levels to reduced breast cancer risk could have been influenced by these factors.
Despite promising results from previous studies, the researchers in this study concluded that there is not a causal relationship between calcium and vitamin D supplementation and reduced risk of breast cancer. It is important to note, however, that some research indicates that higher doses of vitamin D (1000-2000 IU/day) may be needed to prevent cancer. Thus, it is possible that the lower dose of 400 IU of vitamin D in this study may have been insufficient to prevent breast cancer. Research into this topic will likely be ongoing.
 Chlebowski RT, Johnson KC, Kooperberg C, et al. Calcium plus vitamin d supplementation and the risk of breast cancer. Journal of the National Cancer Institute. 2008; 100: 1581-1591.
 Wei MY, Garland CF, Gorham ED. Vitamin D and prevention of colorectal adenoma: A meta-analysis. Cancer Epidemiology, Biomarkers and Prevention. 2008;17(11):2958-2969.
 Goodwin P, Ennis M, Pritchard K, Koo J, Hood N. Vitamin D is common at breast cancer diagnosis and is associated with a significantly higher risk of distant recurrence and death in a prospective cohort study of T1-3, N0-1, M0 BC. Early Release Proceedings from the 2008 American Society of Clinical Oncology. Abstract #511.
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