According to results from the Women’s Health Initiative (WHI) presented at the 2006 annual meeting of the American Society of Clinical Oncology (ASCO), use of calcium plus vitamin D supplements does not reduce the risk of breast cancer in postmenopausal women.
The Women’s Health Initiative (WHI) was designed to address the most common causes of death, disability, and impaired quality of life in postmenopausal women. The WHI included a postmenopausal hormone trial, a dietary modification trial, and a trial of calcium plus vitamin D supplementation. A large observational study within the WHI is also allowing researchers to address many important women’s health issues.
The calcium plus vitamin D trial enrolled more than 36,000 women between the ages of 50 and 79. Half the women received calcium and vitamin D (500 mg of elemental calcium and 200 IU of vitamin D3) twice daily, and half the women received a placebo.
- The number of breast cancer cases was similar in the two study groups. In the calcium plus vitamin D group, 528 women developed breast cancer. In the placebo group, 546 women developed breast cancer.
- Breast cancers were smaller at the time of diagnosis among women in the calcium plus vitamin D group.
The researchers concluded that among healthy postmenopausal women, the use of calcium plus vitamin D supplements does not appear to reduce the risk of developing breast cancer, although cancers were somewhat smaller among the women taking calcium plus vitamin D.
During a discussion of these results, it was noted that study participants were allowed to take dietary supplements outside of the study. This may have obscured a benefit of supplementation because some women assigned to the placebo group took supplements on their own. Furthermore, the optimal dose of vitamin D remains uncertain.
 Chlebowski RT, Johnson KC, Kooperberg C et al. The Women’s Health Initiative Randomized Trial of Calcium Plus Vitamin D: Effects on Breast Cancer and Arthralgias. Presented at the 2006 ASCO Annual Meeting. Abstract LBA6.