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 .
The Effect of Calcium plus Vitamin D on Risk for Invasive Cancer: Results of the Women's Health Initiative (WHI) Calcium Plus Vitamin D Randomized Clinical Trial
In the Women 's Health Initiative ( WHI ) trial of calcium plus vitamin D ( CaD ) , we examined the treatment effect on incidence and mortality for all invasive cancers . Postmenopausal women ( N = 36,282 ) were r and omized to 1,000 mg of elemental calcium with 400 IU vitamin D3 or placebo . Cox models estimated risk of cancer incidence and mortality . After 7.0 yr , 1,306 invasive cancers were diagnosed in the supplement and 1,333 in the placebo group [ hazard ratio ( HR ) = 0.98 ; CI = 0.90 , 1.05 , unweighted P = 0.54 ] . Mortality did not differ between supplement ( 315 , annualized% = .26 ) and placebo [ ( 347 , 0.28 % ; P = 0.17 ; HR = 0.90 ( 0.77 , 1.05 ) ] . Significant treatment interactions on incident cancer were found for family history of cancer , personal total intake of vitamin D , smoking , and WHI dietary trial r and omized group . Calcium/vitamin D supplementation did not reduce invasive cancer incidence or mortality . Supplementation lowered cancer risk in the WHI healthy diet trial arm and in women without a first-degree relative with cancer . The interactions are only suggestive given multiple testing considerations . The low vitamin D dose provided , limited adherence , and lack of serum 25(OH)D values should be considered when interpreting these findings
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 .