Risks associated with sitting and physical inactivity are not comparable to those of smoking (Letter to the Editor)

By Brigid M. Lynch, Paul A. Gardiner, Jeff K. Vallance, Terry Boyle, Neville Owen and Ron Borland

Letter in Response to Online First Article (8 January 2018) “Infographic: Physical activity, sitting time and mortality.

Ekelund’s Infographics piece1 provides an overview of the Ekelund et al.2 harmonised meta-analysis of the joint effects of self-reported sitting and physical activity on all-cause mortality.  This meta-analysis found a clear dose-response association with mortality, such that combined high sitting (>8-h/day) and low physical activity (<2.5 MET-h/day) was associated with the greatest risk (HR=1.59; 95% CI: 1.52, 1.66), compared to combined low sitting (<4-h/day) and high physical activity (>35.5 MET-h/wk).  Ekelund et al.’s meta-analysis demonstrated that high physical activity completely attenuated the effects of sitting, suggesting that physical activity is an effective counter measure to address increasing volumes of sedentary behaviour.2

The infographic clearly communicates the risks of sitting and the benefits of physical activity, and will likely be a helpful resource for public health practitioners.  However, we suggest a revision to remove the comparison of sitting with smoking.  Ekelund states that the 59% increased risk of mortality for high sitting/low physical activity “is similar to that of smoking”1 and cites Schumacher et al.’s results derived from replicating the meta-analysis performed for the landmark 1964 U.S. Surgeon General’s report on smoking and health, using contemporary meta-analytic methods.3

Schumacher et al.’s letter is not an appropriate reference in this context, primarily because it presents risks derived from cohort studies established in the 1950s.3  The health risks associated with smoking have become stronger over time,4 driven by a generational shift toward starting smoking in adolescence, and changes to cigarette design that promote deeper inhalation of smoke.5  Further, Schumacher et al. present risks derived from current vs. never smokers, rather than highest vs. lowest categories of smoking.  Grouping smokers together (regardless of consumption) does not account for the dose-response nature of the smoking-mortality association, meaning results cannot be fairly compared to the effects presented by Ekelund et al.2

Findings from contemporary cohort studies give more reasonable risk estimates for smoking-related all-cause mortality.  The relative risk for smoking 20-39 cigarettes per day vs. none is 3.33 (95% CI: 3.19, 3.48) for men, and 3.48 for women (95% CI: 3.30, 3.67).4  These risks are four times the all-cause mortality risk associated with combined high sitting/low physical activity.  Risks associated with > 40 cigarettes per day are even higher.4

Distorted information regarding the health risks of personal behaviours can lead to distrust of public health messages.6  Equating sitting with smoking is misleading, may reduce the perceived risk of smoking, and could erode hard-won tobacco control gains.

Corresponding author: A/Prof Brigid M. Lynch, brigid.lynch@cancervic.org.au, 615 St Kilda Rd, Melbourne VIC 3004, Australia.

 Disclosures

Lynch is supported by a fellowship from the National Breast Cancer Foundation (ECF-15-

012).  Gardiner is supported by a National Health and Medical Research Council (NHMRC) -Australian Research Council Dementia Research Development Fellowship.  Vallance is supported by the Canada Research Chairs program and a Population Health Investigator Award from Alberta Innovates-Health Solutions.  Boyle is supported by a National Health and Medical Research Council Early Career Fellowship (Australia). Owen is supported by a NHMRC Senior Principal Research Fellowship and NHMRC Centre for Research Excellence grant.

References

  1. Ekelund U. Infographic: Physical activity, sitting time and mortality. BritishJournal of Sports Medicine. In press.
  2. Ekelund U, Steene-Johannessen J, Brown WJ, et al. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet. 2016;388:1302-10.
  3. Schumacher M, Rucker G, Schwarzer G. Meta-analysis and the Surgeon General’s report on smoking and health. The New England Journal of Medicine 2014;370:186-8.
  4. Thun MJ, Carter BD, Feskanich D, et al. 50-year trends in smoking-related mortality in the United States. The New England Journal of Medicine 2013;368:351-64.
  5. Thun MJ, Lopez AD, Hartge P. Smoking-related mortality in the United States. The New England Journal of Medicine 2013;368:1753.
  6. Nagler RH. Adverse outcomes associated with media exposure to contradictory nutrition messages. Journal of Health Communication 2014;19:24-40.

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