title: Vitamin D supplements and cancer incidence and mortality: a meta-analysis.
abstract: BACKGROUND
  Observational studies suggest that effects of vitamin D may be stronger for cancer mortality than for incidence. Yet, existing randomised controlled trials (RCTs) of vitamin D supplementation have limited power to examine the relationships as their primary end points are not cancer incidence or mortality.
  
  
  METHODS
  Meta-analyses of RCTs of vitamin D supplementation and total cancer incidence and mortality were conducted.
  
  
  RESULTS
  Over 2-7 years of duration, vitamin D supplementations had little effect on total cancer incidence (400-1100 IU per day, summary relative risk (RR)=1.00, 95% confidence interval (CI)=0.94-1.06, I(2)=0%; four RCTs with combined 4333 cases), but significantly reduced total cancer mortality (400-833 IU per day, summary RR=0.88, 95% CI=0.78-0.98, I(2)=0%, three RCTs with combined 1190 deaths).
  
  
  CONCLUSIONS
  Over 2-7 years of duration, the benefit of vitamin D supplementation may be limited to cancer mortality.
authors.affiliation: Departments of Nutrition and Epidemiology, Harvard School of Public Health, Building 2, 3rd floor, 655 Huntington Avenue, Boston, MA 02115, USA.
authors.forename: N
authors.initials: N
authors.lastname: Keum
authors.affiliation: 1] Departments of Nutrition and Epidemiology, Harvard School of Public Health, Building 2, 3rd floor, 655 Huntington Avenue, Boston, MA 02115, USA [2] Channing Division of Network Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA.
authors.forename: E
authors.initials: E
authors.lastname: Giovannucci
mesh_terms: D019587:Dietary Supplements; D006801:Humans; D015994:Incidence; D009026:Mortality; D009369:Neoplasms / Q000453:epidemiology* / Q000401:mortality*; D014807:Vitamin D
chemical_list: D014807:Vitamin D