Occupational and leisure time physical activity: risk of all-cause mortality and myocardial infarction in the Copenhagen City Heart Study. A prospective cohort study

OBJECTIVES Men with low physical fitness and high occupational physical activity are recently shown to have an increased risk of cardiovascular disease and all-cause mortality. The association between occupational physical activity with cardiovascular disease and all-cause mortality may also depend on leisure time physical activity. DESIGN A prospective cohort study. SETTING The Copenhagen City Heart Study. PARTICIPANTS 7819 men and women aged 25-66 years without a history of cardiovascular disease who attended an initial examination in the Copenhagen City Heart Study in 1976-1978. OUTCOME MEASURES Myocardial infarction and all-cause mortality. Occupational physical activity was defined by combining information from baseline (1976-1978) with reassessment in 1981-1983. Conventional risk factors were controlled for in Cox analyses. RESULTS During the follow-up from 1976 to 1978 until 2010, 2888 subjects died of all-cause mortality and 787 had a first event of myocardial infarction. Overall, occupational physical activity predicted all-cause mortality and myocardial infarction in men but not in women (test for interaction p=0.02). High occupational physical activity was associated with an increased risk of all-cause mortality among men with low (HR 1.56; 95% CI 1.11 to 2.18) and moderate (HR 1.31; 95% CI 1.05 to 1.63) leisure time physical activity but not among men with high leisure time physical activity (HR 1.00; 95% CI 0.78 to 1.26) (test for interaction p=0.04). Similar but weaker tendencies were found for myocardial infarction. Among women, occupational physical activity was not associated with subsequent all-cause mortality or myocardial infarction. CONCLUSIONS The findings suggest that high occupational physical activity imposes harmful effects particularly among men with low levels of leisure time physical activity.