What is the clinical evidence from this study?

Study design: Cohort. Population: Acute myocardial infarction (n=1115413). Intervention: Occupational lifting vs. Lowest exposure category. Primary outcome: Acute myocardial infarction (AMI) (IRR 1.09, 95% CI 1.03-1.15).

What does this research mean for the field?

Long-term occupational lifting is associated with a slightly increased risk of acute myocardial infarction in both men and women. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

November 14, 2019Open Access

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

JBJens Peter BondeUniversity of Copenhagen EFEsben Meulengracht FlachsUniversity of Copenhagen IMIda E H MadsenUniversity of Copenhagen

Key Result

Long-term occupational lifting was associated with a slightly increased risk of acute myocardial infarction in men (IRR 1.09) and women (IRR 1.27) compared to the lowest exposure categories.

Study Design

Type

Cohort (n=1,115,413)

Structured PICO

Does high physical activity at work (lifting and standing/walking) increase the risk of acute myocardial infarction in adult wage earners?

Population

1,115,413 Danish residents who in 1995 at an age of 31-50 years were gainful wage earners with a valid job code. Excluded military employees and those with any type of ischemic heart disease before start of follow-up.

Intervention

High levels of physical activities at work (lifting and standing/walking) assessed by job-exposure matrices (JEM)

Comparator

Lowest exposure category of physical activities at work (lifting and standing/walking)

Outcome

Incident acute myocardial infarction (AMI) (ICD-10 principal diagnosis I21 or prehospital death from AMI)hard clinical

Long-term occupational lifting is associated with a slightly increased risk of acute myocardial infarction, particularly in women, providing limited support for the physical activity paradox.

Main Result

Effect estimate: IRR 1.09 (95% CI 1.03-1.15)

Limitations

Exposure misclassification due to job-exposure matrices
Lack of detailed information on leisure-time physical activity
Residual confounding
Potential for a healthy worker survivor effect

Abstract

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.

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