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 .
Vitamin D(3) is more potent than vitamin D(2) in humans.
BACKGROUND Current unitage for the calciferols suggests that equimolar quantities of vitamins D(2 ) ( D2 ) and D(3 ) ( D3 ) are biologically equivalent . Published studies yield mixed results . OBJECTIVE The aim of the study was to compare the potencies of D2 and D3 . DESIGN The trial used a single-blind , r and omized design in 33 healthy adults .  Calciferols were dosed at 50,000 IU/wk for 12 wk . Principal outcome variables were area under the curve for incremental total 25-hydroxyvitamin D [ 25(OH)D ] and change in calciferol content of sc fat . RESULTS Incremental mean ( sd ) 25(OH)D area under the curve at 12 wk was 1366 ng · d/ml ( 516 ) for the D2-treated group and 2136 ( 606 ) for the D3 ( P < 0.001 ) . Mean ( sd ) steady-state 25(OH)D increments showed similar differences : 24 ng/ml for D2 ( 10.3 ) and 45 ng/ml ( 16.2 ) for D3 ( P < 0.001 ) . Subcutaneous fat content of D2 rose by 50 μg/kg in the D2-treated group , and D3 content rose by 104 μg/kg in the D3-treated group . Total calciferol in fat rose by only 33 ng/kg in the D2-treated , whereas it rose by 104 μg/kg in the D3-treated group . Extrapolating to total body fat D3 , storage amounted to just 17 % of the administered dose . CONCLUSION D3 is approximately 87 % more potent in raising and maintaining serum 25(OH)D concentrations and produces 2- to 3-fold greater storage of vitamin D than does equimolar D2 . For neither was there evidence of sequestration in fat , as had been postulated for doses in this range . Given its greater potency and lower cost , D3 should be the preferred treatment option when correcting vitamin D deficiency
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 .