Walking Pace, Leisure Time Physical Activity, and Resting Heart Rate in Relation to Disease-Specific Mortality in London: 40 Years Follow-Up of the Original Whitehall Study. An Update of Our Work with Professor Jerry N. Morris (1910–2009)
Introduction
Almost six decades ago, amidst concerns regarding the escalating rates of coronary heart disease (CHD), the first empirical investigation of what was subsequently termed the “exercise hypothesis”—physical activity reduces the occurrence of this condition—was undertaken by Jerry Morris and his colleagues at the Medical Research Council Social Medicine Unit within the London School of Hygiene and Tropical Medicine (1). After typically extended scrutiny and deliberation by Jerry—a practice unacceptable in the current scientific environment of publish or perish—that, remarkably, involved corroborating the results in second investigation study, the novel and contentious findings were finally released as two companion papers in the Lancet(2). They showed lower rates of CHD in bus conductors in comparison to less occupationally active bus drivers, and in postmen relative to deskbound telephonists and other office-based employees (2).
As Jerry Morris would freely and frequently articulate, these studies, precisely because they were seminal, were not without their shortcomings. Statistical methods before the proliferation of personal computers were limited in their capacity to explore the issue of confounding: it was possible that higher levels of overweight, high blood pressure, psychosocial stress, and/or preexisting ischaemia in the less active groups, rather than sedentary behavior itself, were at least partially responsible for the increased risk of CHD. Further, the study focused exclusively on job-orientated activity. Mindful of the diminishing role of occupational physical exertion in modern industrialized societies, Morris et al. (3) and subsequently Paffenbarger et al. (4), also showed physical activity in leisure time to be cardioprotective, an effect that held after a range of covariates were taken into account.
Although still failing to feature in risk prediction algorithms, based on a series of cohort studies 5, 6, 7, 8, 9, 10, 11, 12 and the sporadic randomized controlled trial (13), physical activity and its physiological consequence, such as cardiorespiratory fitness 14, 15, are now widely regarded as being etiologically linked to CHD. Indeed, it is testimony to the robustness of this association that these studies, despite their methodological limitations and with few exception 14, 15 often crude measures of physical exertion, have nonetheless almost universally shown support for Morris' hypothesis. As the prospective cohort studies on which these observations are largely based have matured, investigators have taken the opportunity of exploring the role of physical activity in the occurrence of other important somatic diseases such as stroke and site-specific cancers, an area of physical activity epidemiology that still represents a challenge 16, 17.
In this cohort of British male Civil Servants (government employees)—an extended follow-up of an earlier report that we coauthored with Jerry and with which he, true to form, remained largely unimpressed (18)—we explore the association of leisure time physical activity, walking pace, and resting heart rate with disease-specific causes of death. Doubtless Jerry would have provided penetrating comments, with some mischievous observations. He would typically then decline, the invitation to coauthor—as he did with several of our subsequent articles using this material 19, 20, 21, 22, usually citing his lack of involvement in the design of the original study in the 1960s—before steering the conversation to the latest London stage play or novel on which he would make erudite observations, while causing one to regret that one's own interests and energy levels were a fraction of such an engaging, vital, and now, much missed colleague.
Section snippets
Methods
In the Whitehall study, data were collected on 19,019 male, nonindustrial, government employees aged from 40 to 69 years of age when first examined between 1967 and 1970 in London (UK) (23). The men were invited to complete a questionnaire and undergo a medical examination. The details have been described elsewhere (23). In brief, the questionnaire included enquiries about civil service employment grade (an indicator of socio-economic status) (24), smoking habits (25), marital status (26), and
Results
Forty years of follow-up gave rise to 5294 deaths in those with walking pace data, 5279 in those leisure time physical activity data, and 940 in employees with valid resting heart rate values. The relation between the two indices of physical activity, heart rate, and major causes of death are given in Table 1. Men who reported walking more slowly than their peers, who were less active in their leisure time, and whose resting heart rate was high (i.e., lower cardiorespiratory fitness)
Discussion
The main finding of this study was that the two markers of physical activity were inversely related to mortality ascribed to all causes, CHD, respiratory disease, and total cancers during an extended 40 years of follow-up. For other mortality endpoints—stroke (walking pace only), hematopoietic cancer (walking pace only), stomach cancer (leisure time activity only), and rectal cancer (walking pace only)—individual indices showed effects, but not both. By contrast, walking pace was positively
Conclusions
In conclusion, in addition to expected associations with CHD and total mortality, physical activity also seemed to confer protection against mortality from stroke, respiratory disease, hematopoietic cancer, as well as carcinoma of the stomach, bladder, and rectum. Future work exploring the role of physical activity in the etiology of selected cancers is warranted.
The original screening of the Whitehall study was funded by the Department of Health and Social Security and the Tobacco Research
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