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 VITamin D and OmegA-3 TriaL (VITAL): rationale and design of a large randomized controlled trial of vitamin D and marine omega-3 fatty acid supplements for the primary prevention of cancer and cardiovascular disease.
Data from laboratory studies , observational research , and /or secondary prevention trials suggest that vitamin D and marine omega-3 fatty acids may reduce risk for cancer or cardiovascular disease ( CVD ) , but primary prevention trials with adequate dosing in general population s ( i.e. , unselected for disease risk ) are lacking . The ongoing VITamin D and OmegA-3 TriaL ( VITAL ) is a large r and omized , double-blind , placebo-controlled , 2 x 2 factorial trial of vitamin D ( in the form of vitamin D(3 ) [ cholecalciferol ] , 2000 IU/day ) and marine omega-3 fatty acid ( Omacor fish oil , eicosapentaenoic acid [EPA]+docosahexaenoic acid [ DHA ] , 1g/day ) supplements in the primary prevention of cancer and CVD among a multi-ethnic population of 20,000 U.S. men aged ≥ 50 and women aged ≥ 55 . The mean treatment period will be 5 years . Baseline blood sample s will be collected in at least 16,000 participants , with follow-up blood collection in about 6000 participants . Yearly follow-up question naires will assess treatment compliance ( plasma biomarker measures will also assess compliance in a r and om sample of participants ) , use of non- study drugs or supplements , occurrence of endpoints , and cancer and vascular risk factors . Self-reported endpoints will be confirmed by medical record review by physicians blinded to treatment assignment , and deaths will be ascertained through national registries and other sources . Ancillary studies will investigate whether these agents affect risk for diabetes and glucose intolerance ; hypertension ; cognitive decline ; depression ; osteoporosis and fracture ; physical disability and falls ; asthma and other respiratory diseases ; infections ; and rheumatoid arthritis , systemic lupus erythematosus , thyroid diseases , and other autoimmune disorders
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 .