title: Low serum 25-hydroxyvitamin D levels are associated with increased all-cause mortality risk in a general population: the Tromsø study.
abstract: OBJECTIVE
  Ecologic and observational studies have suggested an association between serum 25-hydroxyvitamin D (25(OH)D) levels and cardiovascular disease (CVD) risk factors, CVD mortality, and cancer mortality. Based on this, low serum 25(OH)D levels should be associated with higher all-cause mortality in a general population. This hypothesis was tested in the present study.
  
  
  METHODS
  The Tromsø study is a longitudinal population-based multipurpose study initiated in 1974 with focus on lifestyle-related diseases. Our data are based on the fourth Tromsø study carried out in 1994-1995.
  
  
  METHODS
  Information about death and cause of death was registered by obtaining information from the National Directory of Residents and the Death Cause Registry. Serum 25(OH)D was measured in 7161 participants in the fourth Tromsø study. Results are presented for smokers (n=2410) and non-smokers (n=4751) separately as our immunoassay seems to overestimate 25(OH)D levels for smokers.
  
  
  RESULTS
  During a mean 11.7 years of follow-up, 1359 (19.0%) participants died. In multivariate regression models, there was a significantly increased risk of all-cause mortality (hazard ratio (HR) 1.32, confidence interval (CI) 1.07-1.62) among non-smoking participants in the lowest 25(OH)D quartile when compared with participants in the highest quartile. Equivalent results for smokers were not significant (HR 1.06, CI 0.83-1.35).
  
  
  CONCLUSIONS
  Low serum 25(OH)D levels were associated with increased all-cause mortality for non-smokers, but the results did not reach statistical significance for smokers. However, low 25(OH)D levels are known to be associated with impaired general health, and randomized controlled studies are needed to address the question of causality.
authors.affiliation: Department of Clinical Medicine, University of Tromsø, Tromsø, Norway. moira-ylva.hutchinson@uit.no
authors.forename: Moira Strand
authors.initials: MS
authors.lastname: Hutchinson
authors.forename: Guri
authors.initials: G
authors.lastname: Grimnes
authors.forename: Ragnar Martin
authors.initials: RM
authors.lastname: Joakimsen
authors.forename: Yngve
authors.initials: Y
authors.lastname: Figenschau
authors.forename: Rolf
authors.initials: R
authors.lastname: Jorde
mesh_terms: D000368:Aged; D002318:Cardiovascular Diseases / Q000209:etiology*; D002423:Cause of Death; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D012306:Risk; D012307:Risk Factors; D012907:Smoking / Q000401:mortality; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000401:mortality*
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D