Work and Leisure Time Physical Activity and Mortality in Men and Women from a General Population Sample

Abstract

PURPOSE: The purpose of this study was to examine the long-term relationships between total physical activity and mortality from all causes and coronary heart disease (CHD) in the general population.

METHODS: A prospective design was used, following participants for 29 years, beginning in 1960. The study population consisted of a randomly selected sample of white male (n = 698) and female (n = 763) residents of Buffalo, New York with a 79.0% participation rate and follow-up rates of 96.0% and 90.2% in males and females, respectively. At baseline, comprehensive information was obtained regarding participants' usual physical activity at work and during leisure time.

RESULTS: As of December 31, 1989, three hundred and two (43.3%) men and 276 (41.0%) women died, 109 (15.6%) and 81 (10.6%) from CHD, respectively. In men, a significant interaction was found between activity and body mass index (BMI) for both outcomes. In women, a significant activity by age interaction was observed. In non-obese men (BMI < 27.02), activity was inversely associated with all-cause [relative risk (RR) = 0.59; 95% confidence interval (CI), 0.39–0.89] and CHD mortality (RR = 0.39; 95% CI, 0.18–0.83), independent from the effects of age and education. No such associations were found in obese men and increased risks could not be ruled out. Among women, younger participants (age < 60 years) had a significantly reduced risk of CHD death with increased activity (RR = 0.26; 95% CI, 0.07–0.99). No other significant associations were observed.

CONCLUSIONS: Physical activity favorably influences mortality risks in non-obese men and younger women. Gender-specific factors should be considered for potential effect modification.

Introduction

The relationship between physical activity and chronic disease morbidity and mortality has been the focus of much scientific research 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. The earliest investigations focused predominantly on physical activity performed at work with a number of different chronic disease outcomes 1, 2, 3, 4, 5, 6, 7, 8, 9, 18, 19. Results from these studies have generally been mixed. One potential explanation for the inconclusive findings is that activity levels were often estimated from participants' job descriptions with no individual measures obtained (20). This could increase the risk of misclassification since different persons with the same job title may have a large variability in physical activity. Other potential explanations include the types of activities performed on the job (i.e., isometric vs. isotonic), limited variability in activity at work, and the fact that physical activity outside of work was not considered. Studies of leisure time physical activity have been more consistent in finding a protective effect of increased activity on a number of disease endpoints including both fatal and non-fatal coronary heart disease (CHD) 10, 11, 12, 13, and mortality from all causes 14, 15, 16, 17, total cardiovascular diseases (CVD), total respiratory diseases, total cancers, and total unnatural causes (14).

Few studies have investigated the joint effects of occupational and leisure time physical activity 3, 4, 11, 14, 15, 17. Individuals with sedentary jobs likely perform the bulk of their activity during leisure time, whereas, those in physically demanding occupations may be more active during work than leisure. For women, particularly those who do not work outside the home, typical leisure time activity questions may not appropriately characterize overall activity levels. Studies that do not consider work and leisure time activity may fail to appropriately characterize activity levels.

Among studies that have included both occupational and leisure time activity, the focus has been on very select, predominantly male populations 3, 4, 11, 14, 15, 17. Such populations may differ from the general population in many ways, including demographic (i.e., age distribution, socioeconomic status), physical (i.e., body build), and lifestyle (i.e., diet) characteristics which may have a modifying effect on the relation between activity and health. Use of select populations limits the generalizability of findings.

Therefore, the Buffalo Health Study, a 29-year prospective study, was conducted to determine the long-term relationships between total physical activity and mortality from all-causes and CHD in a randomly-selected general population sample of white men and women. A comprehensive measure of individual physical activity at work and during leisure time at baseline was used to characterize each study participants' usual energy expenditure during a seven-day week. The study design, population, and comprehensive measures enable us to focus on potential gender differences and effect modifiers of the relationship between total physical activity and mortality.