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 .
Effects of Supplemental Vitamin D and Calcium on Oxidative DNA Damage Marker in Normal Colorectal Mucosa: A Randomized Clinical Trial
The exact antineoplastic effects of calcium and vitamin D3 in the human colon are unclear . Animal and in vitro studies show that these two agents reduce oxidative stress ; however , these findings have never been investigated in humans . To address this , we conducted a pilot , r and omized , double-blind , placebo-controlled , 2 × 2 factorial clinical trial to test the effects of calcium and vitamin D3 on a marker of oxidative DNA damage , 8-hydroxy-2′-deoxyguanosine ( 8-OH-dG ) , in the normal colorectal mucosa . Patients ( N = 92 ) with at least one pathology-confirmed colorectal adenoma were treated with 2 g/d calcium and /or 800 IU/d vitamin D3 versus placebo over 6 months . Overall labeling and colorectal crypt distribution of 8-OH-dG in biopsies of normal-appearing rectal mucosa were detected by st and ardized automated immunohistochemistry and quantified by image analysis . After 6 months of treatment , 8-OH-dG labeling along the full lengths of colorectal crypts decreased by 22 % ( P = 0.15 ) and 25 % ( P = 0.10 ) in the calcium and vitamin D3 groups , respectively , but not in the calcium plus vitamin D3 group . The estimated treatment effects were strongest among participants with higher baseline colon crypt vitamin D receptor expression ( P = 0.05 ) . Overall , these preliminary results indicate that calcium and vitamin D3 may decrease oxidative DNA damage in the normal human colorectal mucosa , support the hypothesis that 8-OH-dG labeling in colorectal crypts is a treatable oxidative DNA damage biomarker of risk for colorectal neoplasms , and provide support for further investigation of calcium and vitamin D3 as chemopreventive agents against colorectal neoplasms . Cancer Epidemiol Biomarkers Prev ; 19(1 ) ;
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 .