Acute myocardial infarction in relation to physical activities at work: a nationwide follow-up study based on job-exposure matrices

Objective This study aimed to evaluate sex-specific risks of acute myocardial infarction (AMI) according to lifting and standing/walking at work. Methods The study population included 1.15 million Danish wage earners. Annual job codes from 1976 onwards were linked to specific exposures using job-exposure matrices (JEM). Cases of AMI during follow-up 1996-2016 were retrieved from national registers. Incidence rate ratios (IRR) were computed by Poisson regression adjusting for demographic and JEM-assessed lifestyle factors. Models addressed physical activities at work the previous 0-2 years (short-term risk) and cumulative physical activities (long-term risk). Results During 21.4 million person-years of follow-up, 22 037 AMI occurred in men and 6942 in women. Exposure-response relationships between recent physical activities at work and AMI were not evident. In men, the fully adjusted long-term IRR for the highest of five exposure categories compared to the lowest were 1.09 [95% confidence interval (CI) 1.03-1.15] for lifting and 1.01 (95% CI 0.96-1.07) for standing/walking. In women, the corresponding figures were 1.27 (95% CI 1.15-1.40) and 1.18 (95% CI 1.07-1.30). The latter risk estimate was strongly attenuated, and the trend became insignificant when adjusted for lifting. Findings were only partially supported by sensitivity analyses. Conclusion The study provides limited support to the hypothesis that long-term lifting and standing/walking at work is related to increased risk of AMI. Possible effects of acute physical exertion are not addressed and bias towards the null because of crude exposure assignment cannot be ruled out.