title: Long-term beta-carotene supplementation and risk of type 2 diabetes mellitus: a randomized controlled trial.
abstract: BACKGROUND
  Recent data suggest a protective role of carotenoids in the development of type 2 diabetes mellitus (DM), possibly via an antioxidant effect, but no randomized trial has directly assessed the efficacy of beta-carotene to prevent DM.
  
  
  OBJECTIVE
  To determine whether long-term beta-carotene supplementation reduces the risk of developing type 2 DM.
  
  
  METHODS
  A total of 22, 071 healthy US male physicians aged 40 to 84 years in a randomized, double- blind, placebo-controlled trial, from 1982 to 1995. More than 99% of the participants had complete follow-up (median duration, 12 years).
  
  
  METHODS
  Subjects were randomly assigned to receive beta-carotene (50 mg on alternate days) or placebo.
  
  
  METHODS
  Incidence of type 2 DM.
  
  
  RESULTS
  A total of 10, 756 subjects were assigned to beta-carotene and 10, 712 to placebo. Incidence of type 2 DM did not differ between groups: 396 men in the beta-carotene group and 402 men in the placebo group developed type 2 DM (relative risk, 0.98; 95% confidence interval, 0.85-1.12). The lack of association between beta-carotene supplementation and incidence of type 2 DM persisted despite multivariate adjustment. There was no evidence of benefit when the period of risk was subdivided into years of follow-up or increasing duration of treatment.
  
  
  CONCLUSIONS
  In this trial of apparently healthy men, supplementation with beta-carotene for an average of 12 years had no effect on the risk of subsequent type 2 DM.
authors.affiliation: Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02215, USA. simin.liu@channing.harvard.edu
authors.forename: S
authors.initials: S
authors.lastname: Liu
authors.forename: U
authors.initials: U
authors.lastname: Ajani
authors.forename: C
authors.initials: C
authors.lastname: Chae
authors.forename: C
authors.initials: C
authors.lastname: Hennekens
authors.forename: J E
authors.initials: JE
authors.lastname: Buring
authors.forename: J E
authors.initials: JE
authors.lastname: Manson
mesh_terms: D000328:Adult; D000368:Aged; D000975:Antioxidants / Q000627:therapeutic use*; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology / Q000517:prevention & control*; D019587:Dietary Supplements; D004311:Double-Blind Method; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D012306:Risk; D019207:beta Carotene / Q000627:therapeutic use*
chemical_list: D000975:Antioxidants; D019207:beta Carotene