This study looked at the question: would calcium and vitamin D supplements decrease risk of breast cancer ? 32,282 women were randomized to receive either 1000 mg calcium carbonate and 400 IU vitamin D or placebo. The women were postmenopausal, with no history of breast cancer for the past 10 years. The study was stopped after 7 years.
The study found no difference in the rates of invasive breast cancer (528 cases in Calcium/D group vs. 546 cases in the placebo group) or non-invasive breast cancer. They also reported no difference in joint pains, which was a secondary question of the study.
Several previous retrospective studies (looking back on Ca/Vit D use) did show a benefit. Possible explanations for the lack of effect on breast cancer incidence in this study include:
Too much baseline Vit D use (participants were allowed to have used ~750 IU prior to the study) compared with level of intervention (400 IU) to see an effect from intervention
Not enough Vit D intervention? Need about 3000 IU to achieve serum level of 42 ng/mL, which has been correlated with greatest breast cancer risk decrease
Too much baseline Ca use before randomization (mean intake was 1165 mg, which is close to optimal amount, 1200 mg)
Participation in hormone therapy trial may have confounded effect (this study was part of the WHI hormone trial)
Intervention in the right age group?
At the present time, Ca and Vit D supplementation can not be recommended to prevent breast cancer.
Apr 20, 2010 - Vitamins and calcium supplements are both associated with higher DNA repair capacity and may reduce the risk of breast cancer, according to a study presented at the annual meeting of the American Association for Cancer Research, held from April 17 to 21 in Washington, D.C.