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 .
Long-term vitamin D3 supplementation is more effective than vitamin D2 in maintaining serum 25-hydroxyvitamin D status over the winter months.
Public health recommendations do not distinguish between vitamin D2 and vitamin D3 , yet disagreement exists on whether these two forms should be considered equivalent . The objective of the present study was to evaluate the effect of a daily physiological dose of vitamin D2 or vitamin D3 on 25-hydroxyvitamin D ( 25(OH)D ) status over the winter months in healthy adults living in Dunedin , New Zeal and ( latitude 46 ° S ) . Participants aged 18 - 50 years were r and omly assigned to 25 μg ( 1000 IU ) vitamin D3 ( n 32 ) , 25 μg ( 1000 IU ) vitamin D2 ( n 31 ) or placebo ( n 32 ) daily for 25 weeks beginning at the end of summer . A per- protocol approach , which included ≥ 90 % supplement compliance , was used for all analyses . Serum 25-hydroxyvitamin D3 ( 25(OH)D3 ) , 25-hydroxyvitamin D2 ( 25(OH)D2 ) and parathyroid hormone ( PTH ) were measured at baseline and at 4 , 8 , 13 and 25 weeks . Geometric mean total serum 25(OH)D concentrations ( sum of 25(OH)D2 and 25(OH)D3 ) at baseline was 80 nmol/l . After 25 weeks , participants r and omised to D2 and placebo had a significant reduction in serum 25(OH)D3 concentrations over the winter months compared with vitamin D3-supplemented participants ( both P < 0.001 ) . Supplementation with vitamin D2  increased serum 25(OH)D2 but produced a 9 ( 95 % CI 1 , 17 ) nmol/l greater decline in the 25(OH)D3 metabolite compared with placebo ( P < 0.036 ) . Overall , total serum 25(OH)D concentrations were 21 ( 95 % CI 14 , 30 ) nmol/l lower in participants receiving vitamin D2 compared with those receiving D3 ( P < 0.001 ) , among whom total serum 25(OH)D concentrations remained unchanged . No intervention-related changes in PTH were observed . Daily supplementation of vitamin D3 was more effective than D2 ; however , the functional consequence of the differing metabolic response warrants further investigation
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 .