Women given 2,000 IU vitamin D3 & calcium supplements had 30% lower risk of cancer compared to women taking placebo.

The difference in cancer rates between groups did not reach statistical significance. However, blood levels of vitamin D were significantly lower (32 ng/ml) in women who developed cancer compared to women that did not get cancer and had higher vitamin D levels (42 ng/ml). The average vitamin D level in the women’s blood at the beginning of the study (33 ng/ml) was higher than the usual target levels that currently range from 20-30 ng/ml. This suggests that higher vitamin D levels than are currently recommended may be needed to decrease the risk of cancer.