title: Twenty-four year mortality in World War II US male veteran twins discordant for cigarette smoking.
abstract: BACKGROUND
  This study was undertaken to test the constitutional hypothesis which attributes the association of tobacco smoking with morbidity and mortality to genetic predispositions to smoking and/or disease.
  
  
  METHODS
  Subjects were World War II veterans, born in the US between 1917 and 1927, and surveyed at mean age 47 for present and past smoking habits. Twenty-four year mortality follow-up data were available for 1515 male twin pairs discordant for lifelong cigarette smoking. Using the first or only death of a smoking-discordant pair, 24-year relative risks of mortality were calculated by zygosity, cause of death, amount smoked, and age at death.
  
  
  RESULTS
  We found that active smokers at baseline, regardless of zygosity, had a higher risk of death than their co-twins who had never smoked or quit smoking (monozygotic pairs: relative risk [RR] = 2.5; 95% confidence interval [CI] : 1.3-6.1 and RR = 1.7; 95% CI : 1.2-2.5; dizygotic pairs: RR = 2.4; 95% CI : 1.4-3.8 and RR = 2.0; 95% CI : 1.7-3.3). The elevated risk of death among smokers was due to deaths from lung cancer (monozygotic pairs: RR = 5.0; 95% CI: 2. 6-15.0; dizygotic pairs: RR = 11.0; 95% CI : 4.3-45.0) or deaths from cardiovascular diseases (monozygotic pairs: RR = 3.9; 95% CI : 1.9-115; dizygotic pairs: RR = 2.8; 95% CI : 1.7-4.9). Apart from these findings the relationship of smoking with all-cause mortality was stronger for earlier/younger deaths and for heavy to moderate smoking.
  
  
  CONCLUSIONS
  The present results, from the largest and longest-studied series of smoking-discordant twins negate the constitutional hypothesis that genetic or early shared familial influences underlie the significant association between tobacco smoking and premature mortality.
authors.affiliation: Health Sciences Program, SRI International, Menlo Park, CA, USA.
authors.forename: D
authors.initials: D
authors.lastname: Carmelli
authors.forename: W F
authors.initials: WF
authors.lastname: Page
mesh_terms: D002318:Cardiovascular Diseases / Q000401:mortality; D002423:Cause of Death; D006801:Humans; D008175:Lung Neoplasms / Q000401:mortality; D008297:Male; D012307:Risk Factors; D012907:Smoking / Q000401:mortality*; D014427:Twins; D014481:United States / Q000453:epidemiology; D014728:Veterans