Breast cancer prevention using calcium and vitamin D: a bright future?

Despite aggressive treatment and screening efforts, breast cancer remains the second leading cause of cancer-related deaths among women in the United States (1). Because of the large number of women dying from this disease and the toxicity of breast cancer treatments, recent efforts have focused on identifying effective cancer preventive agents. These efforts have led to the development of antiestrogen agents, such as tamoxifen and raloxifene, which prevent approximately 50% of invasive breast cancers in women who are at high risk for breast cancer. However, the use of these agents for breast cancer prevention has been limited by their toxicity. A large amount of evidence exists to indicate that vitamin D may be a particularly promising cancer preventive agent. Vitamin D is a fat-soluble vitamin that is essential for bone formation and calcium homeostasis. The potential link between vitamin D levels and reduced cancer incidence was suggested by results from epidemiological studies by Garland et al., Giovannucci, and others (2 – 5) and by recent data suggesting a strong association between low vitamin D levels and increased colon cancer risk (6). Several case – control and cohort studies support an inverse relationship between vitamin D intake and breast cancer incidence (7 – 11); however, other studies show either no association or an association with increased breast cancer risk (10 , 12 – 14). In addition, recent studies found that vitamin D defi ciency was linked to poor outcomes in patients with early breast cancer (15). It is against this backdrop that Chlebowski et al. (16) report the results of a randomized controlled clinical trial evaluating the breast cancer preventive effect of vitamin D and calcium supple-mentation. This study, which was compiled from the calcium plus vitamin D (CaD) arm of the Women's Health Initiative (WHI), randomly assigned 36 282 postmenopausal women to receive daily doses of either 1000 mg calcium with 400 IU vitamin D3 supple-mentation or placebo and were followed up for an average of 7 years. To maximize participation and size, the WHI trial had overlapping groups, including a dietary modifi cation (DM) group, a hormone therapy (HT) group, and a CaD group, which was added in the second year of the study. As a result, 69% of women in the calcium with vitamin D trial were also part of the DM group, 54% were part of the HT group, and 14% had participated in both the DM …