title: Trends in reproductive, smoking, and other chronic disease risk factors by birth cohort and race in a large occupational study population.
abstract: OBJECTIVE
  To illustrate the value of cohort studies to assess trends in chronic disease risk factors.
  
  
  METHODS
  In collaboration with the American Registry of Radiologic Technologists and the University of Minnesota, the National Cancer Institute initiated a cohort study of cancer among radiologic technologists. More than 90,000 technologists who responded to a mailed questionnaire were grouped into ten birth cohorts from before 1920 through 1960 and later, and stratified by self-reported racial/ethnic groups. Trends in height, smoking, and reproductive factors were analyzed.
  
  
  RESULTS
  Among the trends observed were that the proportion of young men (< 18 years) smoking generally fell in each birth cohort after 1925, whereas the proportion of young women smoking rose for those born after 1950. Among women born since 1940, the mean age at menarche for white women has remained at 12.5 years, but has declined among black and Asian/Pacific Islander women. Recent birth cohorts (since 1955) show among the highest mean ages at birth of first child (> 26 years), highest rates of nulliparity at age 25 (>/= 63 %), and lowest mean parity levels (< or = 1.7) compared with earlier cohorts.
  
  
  CONCLUSIONS
  Analyses of large cohorts can clarify birth cohort trends in chronic disease risk factors.
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-7238, USA.
authors.forename: D Michael
authors.initials: DM
authors.lastname: Freedman
authors.forename: Robert E
authors.initials: RE
authors.lastname: Tarone
authors.forename: Michele M
authors.initials: MM
authors.lastname: Doody
authors.forename: Aparna
authors.initials: A
authors.lastname: Mohan
authors.forename: Bruce H
authors.initials: BH
authors.lastname: Alexander
authors.forename: John D
authors.initials: JD
authors.lastname: Boice
authors.forename: Martha S
authors.initials: MS
authors.lastname: Linet
mesh_terms: D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001827:Body Height; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000453:epidemiology* / Q000208:ethnology; D016273:Occupational Exposure; D011871:Radiology; D017584:Reproductive History; D012307:Risk Factors; D017678:Sex Distribution; D012737:Sex Factors; D012907:Smoking; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology