There is currently no firm evidence that vitamin D supplementation decreases or increases cancer occurrence in predominantly elderly community-dwelling women .
Vitamin D₃ supplementation  decreased cancer mortality  and vitamin D supplementation  decreased all-cause mortality , but these estimates are at risk of type I errors due to the fact that too few participants were examined , and to risks of attrition bias originating from substantial dropout of participants .
Combined vitamin D₃ and calcium supplements  increased nephrolithiasis , whereas it remains unclear from the included trials whether vitamin D₃ , calcium , or both were responsible for this effect .
BACKGROUND The evidence on whether vitamin D supplementation is effective in decreasing cancers is contradictory .
OBJECTIVES To assess the beneficial and harmful effects of vitamin D supplementation for prevention of cancer in adults .
A randomized controlled trial of calcium plus vitamin D supplementation and risk of benign proliferative breast disease
Experimental evidence provides strong support for anti-carcinogenic effects of calcium and vitamin D with respect to breast cancer . Observational epidemiologic data also provide some support for inverse associations with risk . We tested the effect of calcium plus vitamin D supplementation on risk of benign proliferative breast disease  , a condition which is associated with increased  risk of breast cancer . We used the Women ’s Health Initiative r and omized controlled trial . The 36,282 participants were r and omized either to 500 mg of elemental calcium as calcium carbonate plus 200 IU of vitamin D3 ( GlaxoSmithKline ) twice daily ( n = 18,176 ) or to placebo ( n = 18,106 ) . Regular mammograms and clinical breast exams were performed . We identified women who had had a biopsy for benign breast disease and subjected histologic sections from the biopsies to st and ardized review . After an average follow-up period of 6.8 years , 915 incident cases of benign proliferative breast disease had been ascertained , with 450 in the intervention group and 465 in the placebo group .  Calcium plus vitamin D supplementation was not associated with altered risk of benign proliferative breast disease overall ( hazard ratio = 0.99 , 95 % confidence interval = 0.86–1.13 ) , or by histologic subtype . Risk varied significantly by levels of age at baseline , but not by levels of other variables . Daily use of 1,000 mg of elemental calcium as calcium carbonate plus 400 IU of vitamin D3 for almost 7 years by postmenopausal women did not alter the overall risk of benign proliferative breast disease
There is currently no firm evidence that vitamin D supplementation decreases or increases cancer occurrence in predominantly elderly community-dwelling women .
Vitamin D₃ supplementation  decreased cancer mortality  and vitamin D supplementation  decreased all-cause mortality , but these estimates are at risk of type I errors due to the fact that too few participants were examined , and to risks of attrition bias originating from substantial dropout of participants .
Combined vitamin D₃ and calcium supplements  increased nephrolithiasis , whereas it remains unclear from the included trials whether vitamin D₃ , calcium , or both were responsible for this effect .
BACKGROUND The evidence on whether vitamin D supplementation is effective in decreasing cancers is contradictory .
OBJECTIVES To assess the beneficial and harmful effects of vitamin D supplementation for prevention of cancer in adults .