The role of occupational physical activity on longevity
Authors: Stephanie A Prince, Aviroop Biswas
Journal: The Lancet Public Health (2021)

We read with great interest the Article by Dalene and colleagues.1Dalene 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 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.2Holtermann A Krause N van der Beek AJ Straker L The physical activity paradox: six reasons why occupational physical activity (OPA) does not confer the cardiovascular health benefits that leisure time physical activity does.Br J Sports Med. 2018; 52: 149-150Crossref PubMed Scopus (164) Google Scholar 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. Other prospective studies showing the deleterious health effects of OPA have also controlled for similar socioeconomic and lifestyle factors, while reducing additional sources of residual confounding (eg, adjusting for alcohol, stress, working conditions).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 Furthermore, limitations persist due to measurement issues (eg, self-reported OPA or LTPA, individual income ignoring household status, scarcity of repeated OPA and LTPA measures) and missing data (eg, diet quality or environmental exposures). Additionally, model C adjusts for LTPA; however, tables in the Article's appendix indicate that workers who report heavy labour have significantly higher levels of moderate-intensity and high-intensity LTPA than do sedentary workers. This finding contrasts with the postulated mechanisms in which OPA, by way of physical and mental fatigue, counters participation in LTPA.5Häusser JA Mojzisch A The physical activity-mediated Demand–Control (pamDC) model: Linking work characteristics, leisure time physical activity, and well-being.Work Stress. 2017; 31: 209-232Crossref Scopus (18) Google Scholar We speculate that healthy worker bias might be evident in this sample and suggest that future research examines interactions between OPA and LTPA. Additionally, it is important to recognise that there is a sizeable literature showing vascular strain from prolonged standing, and lifting heavy and awkward loads. Although we recognise that future studies using secondary population-based data are likely to encounter similar methodological issues, to truly overcome previous shortcomings, randomised and population-based studies with repeated measures designed to explore the validity of the paradox are needed. We declare no competing interests. The role of occupational physical activity on longevity – Authors' replyWe thank Prince and Biswas1 for their interest in our Article, which observed positive associations between occupational physical activity and longevity.2 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. 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