title: Long term risk factors for coronary heart disease and stroke: influence of duration of follow-up over four decades of mortality surveillance.
abstract: OBJECTIVE
  While cohort studies have revealed a range of risk factors for coronary heart disease and stroke, the extent to which the strength of these associations varies according to duration of follow-up in studies with extended disease surveillance is unclear. This was the aim of the present study.
  
  
  RESULTS
  Initiated in 1967/70, the original Whitehall study is an on-going cohort study of 15,402 male UK government workers free of coronary heart disease when they took part in a baseline medical examination during which a range of standard risk factors was measured. In analyses in which we stratified by duration of follow-up, there was evidence of time-dependency for most risk factor-disease relationships. Thus, the associations of systolic and diastolic blood pressure, total cholesterol and cigarette smoking with coronary heart disease and stroke diminished in strength with increasing duration of follow-up, whereas the magnitude of the body mass index-coronary heart disease relation was unchanged. For example, the age-adjusted hazard ratios (95% confidence interval) for cigarette smoking (versus never smoked) in relation to coronary heart disease were: 2.49 (1.80, 3.44), 1.65 (1.34, 2.03), 1.36 (1.15, 1.61) and 1.32 (1.10, 1.58) for follow-up periods 0-10, 10-20, 20-30 and 30+ years, respectively.
  
  
  CONCLUSIONS
  Despite a general diminution in the strength of effect over time, even in the fourth decade of follow-up, classic risk factors retained some predictive capacity for coronary heart disease and, to a lesser degree, stroke.
authors.affiliation: Department of Epidemiology and Public Health, University College London, UK david.batty@ucl.ac.uk.
authors.forename: G David
authors.initials: GD
authors.lastname: Batty
authors.affiliation: Department of Epidemiology and Public Health, University College London, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Shipley
authors.affiliation: MRC Integrative Epidemiology Unit, University of Bristol, UK.
authors.forename: George Davey
authors.initials: GD
authors.lastname: Smith
authors.affiliation: Department of Epidemiology and Public Health, University College London, UK.
authors.forename: Mika
authors.initials: M
authors.lastname: Kivimaki
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015897:Comorbidity; D003327:Coronary Disease / Q000175:diagnosis / Q000401:mortality*; D005500:Follow-Up Studies; D006801:Humans; D008019:Life Style; D008297:Male; D008875:Middle Aged; D016272:Occupational Health; D011159:Population Surveillance; D016016:Proportional Hazards Models; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012737:Sex Factors; D020521:Stroke / Q000175:diagnosis / Q000401:mortality*; D013997:Time Factors; D006113:United Kingdom / Q000453:epidemiology
keywords: Epidemiology; ischaemic heart disease; risk factors; stroke