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Cohort study
In people aged over 45, increased time spent sitting daily is associated with increased risk of all-cause mortality independent of physical activity level
  1. Patricia Manns
  1. Department of Physical Therapy, University of Alberta, Edmonton, Alberta, Canada
  1. Correspondence to: Patricia Manns
    Department of Physical Therapy, University of Alberta, 2-50 Corbett Hall, Edmonton, Alberta T6G2G4, Canada; trish.manns{at}ualberta.ca

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Commentary on: van der Ploeg HP, Chey T, Korda RJ, et al. Sitting time and all-cause mortality risk in 222 497 Australian adults. Arch Intern Med 2012;172:494–500.

Implications for practice and research

  • Encouraging and facilitating a decrease in patients’ sitting time, whether during a hospital stay or in the community, may have important public health implications.

  • More research is required to fully determine the impact of greater amounts of sitting on health, and the health effects of an intervention to reduce daily sitting time.

Context

Sedentary behaviour is defined by posture (sitting or lying) and low energy expenditure (<1.5 times the energy expenditure required for rest).1 The health effects of sedentary behaviour or sitting too much are not the same as the health effects of not getting enough moderate intensity physical activity.2 ,3 In 2011, for the first time, an American College of Sports Medicine position stand on exercise included recommendations to decrease and break up sitting time.4 This study examined the association of total daily sitting time with all-cause mortality in a large prospective cohort.

Methods

Baseline data from participants in a prospective cohort study (n=222 497) was linked with death registry information. Self-reported time spent sitting was determined with one question, ‘about how many hours in each 24 h day do you usually spend sitting?’ Sitting time was categorised into quartiles (<4 h daily, 4 to <8 h daily, 8 to <11 h daily, and ≥11 h daily). Information on potential confounding factors was also collected at baseline and included age, gender, educational level, urban/rural residence, physical activity, body mass index, smoking status, self-rated health, and disability. The primary outcome, all-cause mortality, was determined from examination of a provincial registry for births and deaths. The association between the exposure (time spent sitting, in quartiles as described above) and the outcome (risk of death) was analysed using Cox proportional hazard regression models. Hazard ratios (analogous to risk of death) were calculated for each sitting quartile in comparison with the group whose sitting time was <4 h per day. All analyses were adjusted for confounding factors.

Findings

Participants were aged 45 years and older with more than half of the sample (63.8%) between the ages of 45 and 64 at baseline. They were followed for an average of 2.8 years. Younger groups, those with higher education levels, and those who were less physically active, tended to sit the most. Higher levels of daily sitting time were associated with increased all-cause mortality, independent of physical activity levels and body mass index. The findings suggest that increasing sitting time by one category leads to an 11% increase in risk for all-cause mortality. A clear dose response relationship was shown as the people who sat the most and had the lowest levels of physical activity, had the highest all-cause mortality risk. A subgroup of those with heart disease, diabetes, or obesity at baseline (n=52 229) had the greatest mortality risk but the association between decreased sitting and lower mortality risk was consistent with the association found in the full group.

Commentary

This large prospective study adds to the growing evidence that greater amounts of sitting are associated with increased all-cause mortality, independent of physical activity levels. The authors suggest that the benefits of sitting less may be greatest for those with disease or obesity, and that sitting less may be a particularly important health behaviour change for those who do not meet physical activity guidelines. Helping people with chronic illnesses decrease sitting behaviour may be a more feasible and sustainable behaviour change than a change that results in significantly increased physical activity levels.5

The large sample size is a major strength of this study. Primary limitations were the self-report nature of the determination of sitting behaviour, and the relatively short follow-up time (2.8 years). Nevertheless, this study adds to the growing evidence suggesting that health promotion messages should include recommendations to both sit less and meet physical activity guidelines.

View Abstract

Footnotes

  • Competing interests None.

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References