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 .
Calcium plus vitamin D supplementation and the risk of breast cancer.
BACKGROUND Although some observational studies have associated higher calcium intake and especially higher vitamin D intake and 25-hydroxyvitamin D levels with lower breast cancer risk , no r and omized trial has evaluated these relationships . METHODS Postmenopausal women ( N = 36 282 ) who were enrolled in a Women 's Health Initiative clinical trial were r and omly assigned to 1000 mg of elemental calcium with 400 IU of vitamin D(3 ) daily or placebo for a mean of 7.0 years to determine the effects of supplement use on incidence of hip fracture . Mammograms and breast exams were serially conducted . Invasive breast cancer was a secondary outcome . Baseline serum 25-hydroxyvitamin D levels were assessed in a nested case-control study of 1067 case patients and 1067 control subjects . A Cox proportional hazards model was used to estimate the risk of breast cancer associated with r and om assignment to calcium with vitamin D(3 ) . Associations between 25-hydroxyvitamin D serum levels and total vitamin D intake , body mass index ( BMI ) , recreational physical activity , and breast cancer risks were evaluated using logistic regression models . Statistical tests were two-sided . RESULTS Invasive breast cancer incidence was similar in the two groups ( 528 supplement vs 546 placebo ; hazard ratio = 0.96 ; 95 % confidence interval = 0.85 to 1.09 ) . In the nested case-control study , no effect of supplement group assignment on breast cancer risk was seen . Baseline 25-hydroxyvitamin D levels were modestly correlated with total vitamin D intake ( diet and supplements ) ( r = 0.19 , P < .001 ) and were higher among women with lower BMI and higher recreational physical activity ( both P < .001 ) . Baseline 25-hydroxyvitamin D levels were not associated with breast cancer risk in analyses that were adjusted for BMI and physical activity ( P(trend ) = .20 ) . CONCLUSIONS Calcium and vitamin D supplementation did not reduce invasive breast  cancer incidence in postmenopausal women . In addition , 25-hydroxyvitamin D levels were not associated with subsequent breast cancer risk . These findings do not support a relationship between total vitamin D intake and 25-hydroxyvitamin D levels with breast cancer risk
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 .