Long term risk factors for coronary heart disease and stroke: influence of duration of follow-up over four decades of mortality surveillance

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.

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.

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.