Cohort Profile: The Whitehall II study

Abstract

The Whitehall studies have come to be closely associated with the investigation of socioeconomic differences in physical and mental illness and mortality: the social gradient.1,2 That was not the initial purpose of the first Whitehall study. Donald Reid and Geoffrey Rose set up Whitehall, in the 1960s, as a kind of British Framingham:3 ‘Framingham’ insofar as it was a longitudinal study of cardiorespiratory disease and diabetes, looking at individual risk factors for disease; ‘British’ in that it was done on the cheap—a simple screening examination with follow-up limited to deaths identified from the National Health Service Central Registry. Socioeconomic differences were initially not on the agenda. In the 1970s there was a small group of researchers who continued the British tradition that went back to William Farr in the nineteenth century of examining social inequalities in health.4 For the most part, within epidemiology, ‘social class’ was not an object of study but a control variable: a potential confounder that you got rid of in order to arrive at the ‘correct’ conclusion about the association between risk factor and disease. To the extent that there was a focus on inequalities in health, the general view was that poor people got diseases of material deprivation and rich people got heart disease and peptic ulcers. If this perception had been true,5,6 Whitehall showed that it was no longer so. In a population of middle-aged men, all employed in stable jobs in the British Civil Service, there was an inverse social gradient in mortality: the lower the grade, the higher the risk of death. Tenyear follow-up showed that there was a steep inverse relation between grade of employment and death from all causes, from coronary heart disease (CHD), and from non-coronary causes.7 The relative risk of death owing to CHD was 2.2 in clerical compared with senior administrative staff, and 1.6 for those in the intermediate professional and executive grade. The first Whitehall study made clear that inequalities in health were not limited to the health consequences of poverty. Important as that issue remains, the Whitehall question was why there should be a social gradient in disease in people above the poverty threshold. When conventional risk factors were controlled for, two-thirds of the mortality risk differential between the clerical and administrative grades remained unexplained.7,8 Mortality gradients in the study were in the same direction as national social class mortality data,9 but larger. We hypothesized that psychosocial factors and aspects of nutrition other than those affecting plasma cholesterol (which was higher in high grades in Whitehall) might fill in the unexplained part of the social gradient in mortality.7 We therefore set up the Whitehall II study, a new longitudinal study of British civil servants, with the explicit intention of examining reasons for the social gradient in health and disease in men and extending the research to include women.