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

Abstract

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.

Article summary

Article focus

• 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.

• It is unknown if the association between occupational physical activity with cardiovascular disease and all-cause mortality also depends on leisure time physical activity.

Key messages

• This study shows that men with high occupational physical activity have an increased risk of all-cause mortality.

• Leisure time physical activity was found to modify the positive association between occupational physical activity and risk of all-cause mortality. High occupational physical activity imposes harmful effects particularly among men with low levels of leisure time physical activity.

Strengths and limitations of this study

• Study strengths include the long follow-up time, repeated assessment of the occupational physical activity, objective measures of several covariates from clinical examinations, information on outcomes obtained from valid registers, and participation of both sexes. Some limitations are the lack of control for psychosocial work factors and the self-reported exposures.