title: Effects of beta-carotene supplementation on cancer incidence by baseline characteristics in the Physicians' Health Study (United States).
abstract: OBJECTIVE
  The Physicians' Health Study (PHS) was a randomized trial of beta-carotene (50 mg, alternate days) and aspirin in primary prevention of cancer and cardiovascular disease among 22,071 US male physicians. This report updates results for beta-carotene and examines effect modification by baseline characteristics.
  
  
  METHODS
  Beta-carotene's effect on cancer over nearly 13 years was examined overall and within subgroups defined by baseline characteristics using proportional-hazards models.
  
  
  RESULTS
  2667 incident cancers were confirmed, with 1117 prostate, 267 colon, and 178 lung cancers. There were no significant differences with supplementation in total (relative risk (RR) = 1.0, 95% confidence interval (CI) = 0.9-1.0); prostate (RR = 1.0, 95% CI = 0.9-1.1); colon (RR = 0.9, 95% CI = 0.7-1.2); or lung (RR = 0.9, 95% CI = 0.7-1.2) cancer, and no differences over time. In subgroup analyses, total cancer was modestly reduced with supplementation among those aged 70+ years (RR = 0.8, 95% CI = 0.7-1.0), daily drinkers of alcohol (RR = 0.9, 95% CI = 0.8-1.0), and those in the highest BMI quartile (RR = 0.9, 95% CI = 0.7-1.0). Prostate cancer was reduced with supplementation among those in the highest BMI quartile (RR = 0.8, 95% CI = 0.6-1.0), and colon cancer was reduced among daily drinkers of alcohol (RR = 0.5, 95% CI = 0.3-0.8).
  
  
  CONCLUSIONS
  The PHS found no overall effect of beta-carotene on total cancer, or the three most common site-specific cancers. The possibility of risk reduction within specific subgroups remains.
authors.affiliation: Department of Medicine, Brigham and Women's Hospital, Boston, MA 02215, USA. ncook@rics.bwh.harvard.edu
authors.forename: N R
authors.initials: NR
authors.lastname: Cook
authors.forename: I M
authors.initials: IM
authors.lastname: Le
authors.forename: J E
authors.initials: JE
authors.lastname: Manson
authors.forename: J E
authors.initials: JE
authors.lastname: Buring
authors.forename: C H
authors.initials: CH
authors.lastname: Hennekens
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001241:Aspirin / Q000627:therapeutic use; D015992:Body Mass Index; D002318:Cardiovascular Diseases / Q000517:prevention & control; D003110:Colonic Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D004311:Double-Blind Method; D006801:Humans; D015994:Incidence; D008019:Life Style; D008175:Lung Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology / Q000517:prevention & control*; D010820:Physicians; D011471:Prostatic Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D019207:beta Carotene / Q000627:therapeutic use*
chemical_list: D019207:beta Carotene; D001241:Aspirin