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 .
Bioavailability of vitamin D(2) and D(3) in healthy volunteers, a randomized placebo-controlled trial.
BACKGROUND The bioequivalence of the different forms of vitamin D , ergocalciferol ( vitamin D2 ) and cholecalciferol ( vitamin D3 ) , has been question ed . Earlier studies have suggested that vitamin D2 is less biologically active than vitamin D3 . OBJECTIVE AND DESIGN In a parallel study , we tested the effects of supplementation with 50-μg/d doses of vitamin D2 or D3 or a placebo over a period of 8 weeks on 25(OH)D2 , 25(OH)D3 , their sum 25(OH)D ( primary outcome variables ) , and PTH in healthy volunteers applying a double-blind , r and omized study design . The study was conducted during the winter of 2012 in Halle ( Saale ) , Germany , at latitude 51 ° 47N , when UVB irradiation is virtually absent .  Blood sample s for the determinations of vitamin D status and PTH were collected at baseline and after 4 and 8 weeks of supplementation . RESULTS In the placebo  group ( n = 19 ) , 25(OH)D3 decreased from 39.4 ± 14.2 to 31.1 ± 12.4 nmol/L after 8 weeks ( P < .01 ) . In the vitamin D3 group ( n = 42 ) , the concentrations of 25(OH)D3 increased from 41.5 ± 22.8 nmol/L at baseline to 88.0 ± 22.1 nmol/L after 8 weeks ( P < .01 ) . In the group receiving vitamin D2 ( n = 46 ) , the 25(OH)D2 concentrations increased significantly , whereas the 25(OH)D3 concentration fell from 36.4 ± 13.3 nmol/L at baseline to 16.6 ± 6.3 nmol/L after 8 weeks ( P < .01 ) . The total 25(OH)D was not different between the groups at baseline but differed significantly between the groups after 4 and 8 weeks ( P < .001 ) . CONCLUSIONS Vitamin D3  increases the total 25(OH)D concentration more than vitamin D2 . Vitamin D2 supplementation was associated with a decrease in 25(OH)D3 , which can explain the different effect on total
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 .