The role of occupational physical activity on longevity – Authors' reply
Authors: Knut Eirik Dalene, Jakob Tarp, Ulf Ekelund
Journal: The Lancet Public Health (2021)

We thank Prince and Biswas1Prince SA Biswas A The role of occupational physical activity on longevity.Lancet Public Health. 2021; 6: e544Summary Full Text Full Text PDF Scopus (1) Google Scholar for their interest in our Article, which observed positive associations between occupational physical activity and longevity.2Dalene KE Tarp J Selmer RM et al.Occupational physical activity and longevity in working men and women in Norway: a prospective cohort study.Lancet Public Health. 2021; 6: e386-e395Summary Full Text Full Text PDF PubMed Scopus (9) Google Scholar The authors raise concerns about residual confounding and a potential healthy worker bias. We did not have information on diet, alcohol consumption, stress, or working conditions, but speculate that adjustments for these variables would favour individuals with less physically demanding occupations. Thus, we contend that it is unlikely that our results are explained by residual confounding as suggested by Prince and Biswas.1Prince SA Biswas A The role of occupational physical activity on longevity.Lancet Public Health. 2021; 6: e544Summary Full Text Full Text PDF Scopus (1) Google Scholar Furthermore, we included a population-based sample with a high participation rate and low baseline age, many of whom were recruited during the 1970s and 1980s when physically active work was still common. Taken together, these factors reduce the risk of healthy worker bias. A unique feature of our study is the adjustment for highest income and educational level attained across several censuses, essentially the type of repeated measures information that Prince and Biswas call for.1Prince SA Biswas A The role of occupational physical activity on longevity.Lancet Public Health. 2021; 6: e544Summary Full Text Full Text PDF Scopus (1) Google Scholar The authors quote two studies with associations in the opposite direction to those that we observed.3Smith P Ma H Glazier RH Gilbert-Ouimet M Mustard C The relationship between occupational standing and sitting and incident heart disease over a 12-year period in Ontario, Canada.Am J Epidemiol. 2018; 187: 27-33Crossref PubMed Scopus (37) Google Scholar, 4Holtermann A Schnohr P Nordestgaard BG Marott JL The physical activity paradox in cardiovascular disease and all-cause mortality: the contemporary Copenhagen General Population Study with 104 046 adults.Eur Heart J. 2021; 42: 1499-1511Crossref PubMed Scopus (20) Google Scholar However, one of these studies showed that, in men, occupations involving a combination of sitting, standing, and walking were associated with a lower risk of heart disease than were sitting occupations (HR 0·49, 95% CI 0·27–0·88).3Smith P Ma H Glazier RH Gilbert-Ouimet M Mustard C The relationship between occupational standing and sitting and incident heart disease over a 12-year period in Ontario, Canada.Am J Epidemiol. 2018; 187: 27-33Crossref PubMed Scopus (37) Google Scholar Thus, higher (occupational) physical activity energy expenditure appears to be beneficial. The study also reported that occupations predominantly involving standing were associated with an increased risk of heart disease (2·06, 1·00–4·24). These findings reveal a crucial nuance in the so-called physical activity paradox debate. Imagine a shop worker with 4–5 h of standing and approximately 8000 steps of walking per workday. Mounting evidence suggests that the 8000 steps of walking per workday would contribute positively to health through an increase in physical activity energy expenditure, and that this effect is largely independent of physical activity intensity and, thus, cardiorespiratory fitness adaptations.5Saint-Maurice PF Troiano RP Bassett Jr, DR et al.Association of daily step count and step intensity with mortality among US adults.JAMA. 2020; 323: 1151-1160Crossref PubMed Scopus (104) Google Scholar However, the 4–5 h of standing might have unfavourable effects on the vascular and musculoskeletal system. Therefore, the net effect on health could be a mixture of exposures, some beneficial and others detrimental. This distinction is lost when occupational physical activity is used as an umbrella term to describe the effect of physical activity energy expenditure, postures, and job types. Although this shop worker would have a higher physical activity energy expenditure during work than would a sedentary office worker, simply standing up increases energy expenditure to a minor extent.6Saeidifard F Medina-Inojosa JR Supervia M et al.Differences of energy expenditure while sitting versus standing: a systematic review and meta-analysis.Eur J Prev Cardiol. 2018; 25: 522-538Crossref PubMed Scopus (25) Google Scholar We believe that the debate about a physical activity paradox would benefit from a clearer distinction between physical activity energy expenditure, postures, and job types, particularly because job type has implications for many additional factors (eg, environmental exposures, autonomy, enjoyment, and stress), in addition to strong associations with socioeconomic circumstances. We declare no competing interests. The role of occupational physical activity on longevityWe read with great interest the Article by Dalene and colleagues.1 We commend the authors for using a large population-based sample linked to registry data to further investigate the so-called physical activity paradox, whereby leisure-time physical activity (LTPA) and strenuous occupational physical activity (OPA) have been described as having opposite effects on health.2 However, we disagree with the authors' assertion that their study overcomes shortcomings of previous work exploring associations between OPA and longevity by adjusting for more detailed socioeconomic (ie, highest education and income), smoking status, and measured anthropometric data. Full-Text PDF Open AccessOccupational physical activity and longevity in working men and women in Norway: a prospective cohort studyOur results suggest that moderate to high occupational physical activity contributes to longevity in men. However, occupational physical activity does not seem to affect longevity in women. These results might inform future physical activity guidelines for public health. Full-Text PDF Open Access