title: Meta-analysis of long-term vitamin D supplementation on overall mortality.
abstract: BACKGROUND
  It has been suggested that vitamin D is effective to prevent mortality. However, there is no consistent conclusion that the effects of vitamin D supplementation on all-cause mortality are associated with duration of treatment. We conducted a meta-analysis regarding this issue in an effort to provide a more robust answer.
  
  
  METHODS
  A comprehensive search in a number of databases, including MEDLINE, Embase and The Cochrane Central Register of Controlled Trials, was conducted for collecting randomized controlled trials (RCTs) on vitamin D supplementation preventing mortality. Two investigators independently screened the literature according to the inclusive and exclusive criteria and the relative data were extracted. Data analysis was performed by using Review Manager 5.0 software.
  
  
  RESULTS
  Data from forty-two RCT s were included. Vitamin D therapy significantly decreased all-cause mortality with a duration of follow-up longer than 3 years with a RR (95% CI) of 0.94 (0.90-0.98). No benefit was seen in a shorter follow-up periods with a RR (95% CI) of 1.04 (0.97-1.12). Results remain robust after sensitivity analysis. The following subgroups of long-term follow-up had significantly fewer deaths: female only, participants with a mean age younger than 80, daily dose of 800 IU or less, participants with vitamin D insufficiency (baseline 25-hydroxyvitamin D level less than 50 nmol/L) and cholecalciferol therapy. In addition, the combination of vitamin D and calcium significantly reduced mortality and vitamin D alone also had a trend to decrease mortality in a longer time follow up.
  
  
  CONCLUSIONS
  The data suggest that supplementation of vitamin D is effective in preventing overall mortality in a long-term treatment, whereas it is not significantly effective in a treatment duration shorter than 3 years. Future studies are needed to identify the efficacy of vitamin D on specific mortality, such as cancer and cardiovascular disease mortality in a long-term treatment duration.
authors.affiliation: Department of Pharmacology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Yayuan
authors.initials: Y
authors.lastname: Zheng
authors.affiliation: Department of Pharmacology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Jianhong
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Department of Pharmacology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Manru
authors.initials: M
authors.lastname: Zhou
authors.affiliation: Department of Pharmacology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Liao
authors.initials: L
authors.lastname: Cui
authors.affiliation: Institute of Respiratory Disease, Guangdong Medical College, Zhanjiang, China.
authors.forename: Weimin
authors.initials: W
authors.lastname: Yao
authors.affiliation: Department of Pharmacology, Guangdong Medical College, Zhanjiang, China.
authors.forename: Yuyu
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D019587:Dietary Supplements; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009026:Mortality; D017594:Publication Bias; D014807:Vitamin D / Q000494:pharmacology*
chemical_list: D014807:Vitamin D