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 .
Prognostic effects of 25-hydroxyvitamin D levels in early breast cancer.
PURPOSE Vitamin D has been linked to breast cancer risk , but prognostic effects are unknown . Such effects are biologically plausible given the presence of vitamin D receptors in breast cancer cells , which act as nuclear transcription factors to regulate gene activity . PATIENTS AND METHODS The study was conducted in a prospect i ve inception cohort of 512 women with early breast cancer diagnosed 1989 to 1996 .  Vitamin D levels were measured in stored blood . Clinical , pathologic , and dietary data were accessed to examine prognostic effects of vitamin D. RESULTS Mean age was 50.4 years , mean vitamin D was 58.1 + /- 23.4 nmol/L.  Vitamin D levels were deficient ( < 50 nmol/L ) in 37.5 % of patients , insufficient ( 50 to 72 nmol/L ) in 38.5 % of patients , and sufficient ( > 72 nmol/L ) in 24.0 % of patients . There was little variation in mean vitamin D levels between summer and winter months . Mean follow-up was 11.6 years ; 116 women had distant recurrences , and 106 women died . Women with deficient vitamin D levels had an increased risk of distant recurrence ( hazard ratio [ HR ] = 1.94 ; 95 % CI , 1.16 to 3.25 ) and death ( HR = 1.73 ; 95 % CI , 1.05 to 2.86 ) compared with those with sufficient levels . The association remained after individual adjustment for key tumor and treatment related factors but was attenuated in multivariate analyses ( HR = 1.71 ; 95 % CI , 1.02 to 2.86 for distant recurrence ; HR = 1.60 ; 95 % CI , 0.96 to 2.64 for death ) . CONCLUSION Vitamin D deficiency may be associated with poor outcomes in breast cancer
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 .