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Evidence of Health Risks from Occupational Sitting

Where Do We Stand?
      Although there has been renewed research interest in the study of sedentary behavior, evidence linking occupational sitting to cardiovascular health dates back to the pioneering work of Jerry Morris in the 1950s.
      • Morris J.N.
      • Heady J.A.
      • Raffle P.A.
      • Roberts C.G.
      • Parks J.W.
      Coronary heart-disease and physical activity of work.
      In a seminal epidemiologic study, Dr. Morris and his colleagues found that seated workers (London bus drivers and mail sorters) had higher rates of cardiovascular events than employees who stood and walked while working (ticket collectors and postal workers).
      Until recently, the health risks associated with a sedentary lifestyle were thought to be a result of insufficient moderate-to-vigorous physical activity, leading many to incorrectly assume that sedentary behavior and physical activity were opposite ends of the same continuum. To our knowledge, this assumption was first challenged by Owen and colleagues,
      • Owen N.
      • Leslie E.
      • Salmon J.
      • Fotheringham M.J.
      Environmental determinants of physical activity and sedentary behaviour.
      who reported that the determinants of sedentary behavior and physical activity might be distinct. In the past 10 years, more than 300 published studies have measured sedentary behavior as a concept distinct from physical activity, and there is now widespread conceptual and empirical support
      • Biddle S.J.
      • Gorely T.
      • Marshall S.J.
      • Murdey I.
      • Cameron N.
      Physical activity and sedentary behaviours in youth: issues and controversies.
      • Hamilton M.T.
      • Healy G.N.
      • Dunstan D.W.
      • Zderic T.W.
      • Owen N.
      Too little exercise and too much sitting: inactivity physiology and the need for new recommendations on sedentary behavior.
      • Katzmarzyk P.T.
      • Church T.S.
      • Craig C.L.
      • Bouchard C.
      Sitting time and mortality from all causes, cardiovascular disease, and cancer.
      • Owen N.
      • Healy G.N.
      • Matthews C.E.
      • Dunstan D.W.
      Too much sitting: the population health science of sedentary behavior.
      that the two exert independent and interdependent influences on health. Over the past 5 years, state-of-the-science papers on inactivity physiology have been published by Marc Hamilton and colleagues,
      • Bey L.
      • Hamilton M.T.
      Suppression of skeletal muscle lipoprotein lipase activity during physical inactivity: a molecular reason to maintain daily low-intensity activity.
      • Hamilton M.
      • Hamilton D.G.
      • Zderic T.W.
      Exercise physiology versus inactivity physiology: an essential concept for understanding lipoprotein lipase regulation.
      • Hamilton M.T.
      • Hamilton D.G.
      • Zderic T.W.
      Role of low energy expenditure and sitting in obesity, metabolic syndrome, type 2 diabetes, and cardiovascular disease.
      who have started to piece together a compelling case that different physiologic mechanisms may be operating during periods of muscular unloading compared to periods of exercise. Physiologic mechanisms observed during periods of inactivity may have an indirect influence on our cardiometabolic health because of their role in triglyceride uptake, HDL cholesterol production, and glucose transport.
      • Hamilton M.T.
      • Hamilton D.G.
      • Zderic T.W.
      Role of low energy expenditure and sitting in obesity, metabolic syndrome, type 2 diabetes, and cardiovascular disease.
      The research literature on sedentary behavior and health has been dominated by studies about relationships between TV viewing and pediatric obesity. Studies on the deleterious effects of prolonged sitting during adulthood have only recently started to emerge. Occupational sitting in particular is an area of focused interest because many of us are likely to spend more than half of our working day in a seated position. However, many of the studies we do have are scattered across diverse literatures with relevant data buried in the lower tables of papers published with a different purpose. This situation might be considered similar to what Bernard Forscher, of the Mayo Clinic, once described as “Chaos in the Brickyard”
      • Forscher B.K.
      Chaos in the brickyard.
      in his satirical letter to Science more than 45 years ago. With great metaphorical eloquence, Dr. Forscher complained of the excessive production of studies (bricks tossed onto a pile) with little regard for the systematic building of cumulative evidence (an edifice). Over time, the true edifice becomes harder and harder to see among the piles of bricks. This is not meant as a criticism of broad-focused empirical study but instead underscores the importance of conducting rigorous systematic reviews of the literature in scientific subfields that are developing rapidly; or to state a dictum of the meta-analyst: we may have already proven a lot more than we actually know.
      The systematic review on occupational sitting and long-term health risk published by van Uffelen and colleagues
      • van Uffelen J.G.Z.
      • Wong J.
      • Chau J.Y.
      • et al.
      Occupational sitting and health risks: a systematic review.
      in this issue of the American Journal of Preventive Medicine is the first critical synthesis of associations between sitting at work and body fatness, cancer, cardiovascular disease, type 2 diabetes, and mortality. Importantly, the authors searched six electronic databases to locate relevant studies published in peer-reviewed journals spanning eight languages (English, German, French, Chinese, Dutch, Italian, Norwegian, and Spanish). Forty-three studies were abstracted and assessed by two independent reviewers, thereby strengthening the validity of the review. Using accepted causality criteria, van Uffelen and colleagues conclude that there is currently insufficient evidence of a causal relationship between occupational sitting and health risk.
      The health risk that has received the most study was cancer (17 studies; 36% of total studies), with five of the 17 studies reporting significant positive associations. The health risk that has been studied the least is diabetes (9%), but the majority of these (75%) reported positive associations. This suggests clearly that further study is warranted on the relationships between sitting at work and markers of glycemic control. Of note is that only 43% of studies adjusted for levels of physical activity, which makes it difficult to untangle the independent effects of prolonged sitting on health. When studies that adjusted for physical activity were examined, 75% found significant associations. Finding more-consistent evidence of a relationship between sitting and health risk after adjustment for physical activity suggests that physical activity and possibly leisure-time sedentary behavior are obscuring true relationships. Overall, the quality of the study designs was good, but it should be noted that the quality rating provided by van Uffelen and colleagues
      • van Uffelen J.G.Z.
      • Wong J.
      • Chau J.Y.
      • et al.
      Occupational sitting and health risks: a systematic review.
      refers to quality of methodologic reporting, not methodologic rigor per se.
      In short, the study by van Uffelen et al.
      • van Uffelen J.G.Z.
      • Wong J.
      • Chau J.Y.
      • et al.
      Occupational sitting and health risks: a systematic review.
      represents a landmark publication for understanding the health risks associated with occupational sitting. Researchers are encouraged to examine these associations in more detail using objective measures of sitting. However, it is also recommended that future studies expand the focus to risks outside of cardiometabolic health. Short-term outcomes (such as musculoskeletal health) have been largely ignored in the sedentary behavior–health risk literature. This may be an unfortunate omission because it is well documented that the constrained and relatively static postures imposed by seated work are risk factors for musculoskeletal ill health. For example, traditional human-factors literature clearly documents the anatomic and physiologic factors involved in the development of low back pain (LBP) from sitting
      • Pheasant S.
      Ergonomics, work and health.
      despite systematic review evidence failing to implicate occupational sitting.
      • Roffey D.M.
      • Wai E.K.
      • Bishop P.
      • Kwon B.K.
      • Dagenais S.
      Causal assessment of occupational sitting and low back pain: results of a systematic review.
      However, seminal epidemiologic data
      • Kelsey J.L.
      An epidemiological study of the relationship between occupations and acute herniated lumbar intervertebral discs.
      demonstrate a link between sedentary occupations and acute herniated lumbar intervertebral discs possibly because of increases in disc pressure when sitting. Environmental influences such as no support for the feet, low-friction seating material, or poor desk height can all create additional muscle work. Poor design forces the adoption of awkward and inefficient working postures that can ultimately lead to discomfort, pain, and chronic disability if adverse conditions persist. Indeed, a recent systematic review
      • Kuoppala J.
      • Lamminpaa A.
      • Husman P.
      Work health promotion, job well-being, and sickness absences—a systematic review and meta-analysis.
      of worksite health promotion efforts reported that sickness absences from work were reduced by activities promoting ergonomics.
      Theory and evidence emphasizes the important role of proximal outcomes in driving intention formation and physical activity behavior change. For worksite programs and policies to advocate new behaviors (such as reductions in occupational sitting), evidence is needed that the consequences are likely to have a direct and immediate impact on factors such as preventable absenteeism, workers compensation claims, disability, and at-work performance deficits.
      • Goetzel R.Z.
      • Ozminkowski R.J.
      The health and cost benefits of work site health-promotion programs.
      In summary, more empirical research is needed across the proximal–distal continuum of risks associated with occupational sitting. Sedentary behavior researchers are encouraged to intensify their research on cardiometabolic outcomes of sitting but also broaden their focus to assess a wider spectrum of deleterious consequences, including musculoskeletal ill health. However, this will require more interdisciplinary and transdisciplinary collaborations with experts in health ergonomics, occupational health and safety, as well as the rehabilitation sciences. This approach—often referred to as team science
      • Stokols D.
      • Hall K.L.
      • Taylor B.K.
      • Moser R.P.
      The science of team science: overview of the field and introduction to the supplement.
      —is important if we are to avoid the silo-based model of knowledge accumulation that has dominated much of our field to date.
      No financial disclosures were reported by the authors of this paper.

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