The Real Risks of Sitting

Review

Biswas A, et al. Sedentary Time and Its Association With Risk for Disease Incidence, Mortality and Hospitalization in Adults: A systematic review and meta-analysis.

Annals of Internal Medicine. 2015; 162: 123-132.

Study Methods

This study was a meta-analysis that examined the association between sedentary behavior and hospitalizations, all-cause mortality, cardiovascular disease, diabetes and cancer in adults.

Sedentary behavior was broadly defined as behavior characterized by low energy expenditure (<1.5 metabolic equivalents), including sitting and reclined posture. “Prolonged sitting” was considered when more than half of a person’s day resulted in low energy expenditure. This study controlled for physical activity to examine sedentary behavior as an independent risk factor.

Results and Outcomes

Of the 20,980 studies were identified, 47 met eligibility criteria. All but 3 of these studies were prospective cohort studies, the remaining were cross-sectional and case-control designs. Sedentary times were generated by self-report in all but one study.

Subjects with prolonged sitting time were 1.24 times more likely to die from all-cause mortality compared to less sedentary adults (95% CI: 1.09-1.41), 1.18 times more likely to die from cardiovascular disease (95% CI: 1.11-1.26), 1.14 times more likely to develop cardiovascular disease (95% CI: 1.00-1.73), 1.17 times more likely to die from cancer (95% CI: 1.11-1.24), and 1.13 times more likely to develop cancer, (95% CI: 1.05-1.21).

Sitting’s greatest risk was correlated with an almost doubling of the risk to develop type-2 diabetes (HR: 1.91, 95% CI: 1.64-2.22). Additionally, several studies found a statistically significant association between sedentary time and mortality and/or incidence of various cancers including breast, colon, colo-rectal, endometrial and epithelial ovarian cancer.

Deleterious health outcomes from prolonged sedentary behavior decreased in magnitude among people who engaged in higher amounts of physical exercise compared to lower levels. Among those who exercised frequently, there was no increase risk for all cause mortality compared to those who did not exercise (1.46 (95% CI: 1.22-1.75)). This equates to 30% relative risk reduction in all-cause mortality among those who engaged in high levels of physical activity compared to low levels.

Conclusion

Prolonged sedentary time was significantly associated with multiple negative health outcomes including all-cause mortality and type-2 diabetes regardless of physical activity. The largest statistical effect was seen with the risk for type-2 diabetes. Physical activity reduced but did not eliminate the association between prolonged sedentary behavior and these negative health outcomes.

Commentary

This study suggests that after statistical adjustment for physical activity, prolonged sedentary time increases risk of all-cause mortality and chronic disease incidence. The results of this meta-analysis bear particular weight because it is based on a large sample size gathered from 14 high quality studies that were primarily prospective cohort studies following populations over time (1).

Based on this meta-analysis, prolonged sedentary behavior is an independent risk factor for chronic disease and premature mortality. Increased time spent in moderate to vigorous physical activity seems to at least partially offset the negative effects of prolonged sitting.

However, moderate amounts of regular physical activity still do not completely neutralize the negative health effects of prolonged sedentary behavior. Sitting for the majority of the day, even while supplementing with 30 minutes of high intensity exercise, for example, is not necessarily as healthy as being lightly active all day.

Prior to this study, the literature has found an association between physical activity and chronic disease and mortality, with public health messages focusing on exercise recommendations (2). Current guidelines by the CDC recommend at least 150 minutes of moderate intensity exercise per week in at least 10-minute spurts and at least 2 days of muscle strengthening activities (3). This meta-analysis implies this minimum requirement of “recommended physical activity” does not negate the negative effects of sitting the vast majority of day.

Major limitations of this meta-analysis were heterogeneity of study designs among the 47 studies included, inconsistent definitions of sedentary time across studies and possible publication bias.

The implications of this meta-analysis are particularly concerning as our society becomes more sedentary in everyday life. It is estimated the US adult population spends 51-68% of total waking hours sedentary and only 5% of total awake time doing moderate to vigorous physical activity (1,2,4). Sedentary behavior is increasingly replacing normal higher energy expenditure in workplace environments, leisure activities and transportation given modern conveniences and technology.

The most prominent result in this meta-analysis was a nearly 2-fold increase in type-2 diabetes incidence among those with prolonged sedentary behavior. A recently published multi-center randomized controlled trial investigated the impact of lifestyle intervention to sedentary time vs. metformin or placebo and the risk of diabetes incidence in 3,234 overweight adults in the US. The study found lifestyle intervention was more effective than metformin or placebo in decreasing disease incidence. Lifestyle intervention goals were at least 7% weight loss and 150 minutes per week of moderate intensity activity. This demonstrates that lifestyle interventions that aim at decreasing sedentary time can be effective, and more effective than pharmacological intervention at reducing chronic diseases that are extremely costly to manage (5,6).

While this analysis shows a correlation between amount of time sitting and risk of death, it does not imply causation. Several confounders may have contributed that were not accounted for in the individual studies, such as socioeconomic status, employment status, genetics or comorbidities. People who lead more sedentary lives may tend to be less healthy overall, or may have a disability that prevents them from being active. Future studies would be helpful to determine potential physiological mechanisms by which sedentary behavior leads to multiple adverse health outcomes described.

This study should urge us to not only be encouraging people to get as much physical activity in the form of exercise that they can (and at least meeting minimum recommendations), but also teach them to reduce their sitting time as its own goal.

Start by convincing our patients to sit less and move more in any small way possible throughout the day. This is a very low cost intervention most people are capable of making. Even standing is better than sitting and may decrease mortality risk (7). Ideally, from a public health perspective, workplaces would move to make it easier and acceptable for employees with sedentary jobs to incorporate movement, or hourly breaks into their workday.

Based on current data, sitting is a threat to health, and appears to be a modifiable risk factor- one that most have the freedom to change today with the simple tools of own mind, body and willpower. Educate patients that sitting is indeed a health risk. Keep the message simple: try to move as often as you can regardless of intensity level. Remind patients that all light activity is better than no activity, and the less they sit, the better their future will be.

References:

1. Biswas A, et al. Sedentary Time and Its Association With Risk for Disease Incidence, Mortality and Hospitalization in Adults: A systematic review and meta-analysis. Annals of Internal Medicine. 2015; 162: 123-132.

2. Dunstan D, Howard B, Healy G, Owen N. Too much sitting- A health hazard. 2012. Diabetes Research and Clinical Practice. 97(3): 368-376. http://www.diabetesresearchclinicalpractice.com/article/S0168-8227%2812%2900208-2/fulltext

3. US Department of Health and Human Services. 2008 Physical Activity Guidelines for Americans. 2008. Washington DC. www.health.gov/paguidelines

4. Matthews, C.E., Chen, K.Y., Freedson, P.S., Buchowski, M.S., Beech, B.M., Pate, R.R. et al. Amount of time spent in sedentary behaviors in the United States, 2003—2004. Am J Epidemiol. 2008; 167: 875–881.

5. Rockette-Wagner B, Edelstein S, Venditti E, Reddy D, Bray G, Carrion-Petersen M, Dabelea D, Delahanty L, Florez H, Franks P, Montez M, Rubin R, Kriska A. 2015. The impact of lifestyle intervention on sedentary time in individuals at high risk of diabetes. Diabetologia.

6. Carlson S, Fulton J, Pratt M, Yang Z, Adams E. Inadequate physical activity and health care expenditures in the United States. 2015. Progress in Cardiovascular Disease. 57(4): 315-23.

7. Van der Ploeg H, Chey T, Ding D, Chau J, Stamatakis E, Bauman A. 2014. Standing time and all-cause mortality in a large cohort of Austrailian adults. Preventative Medicine. 69: 187-91.