Is Sitting the New Smoking?
Make no mistake: sitting less time overall is a good idea for myriad health reasons, but is sitting as bad for you as some would suggest? Is it really the new smoking? In 2017 alone, a slew of new research studies has looked at various health detriments associated with prolonged sitting, even in adults who exercise regularly.
For adults with type 2 diabetes, bouts of either light walking or simple resistance activities benefit not only their glycemic responses to meals (1; 2), but also markers of cardiovascular risk. Both types of interrupting activities are associated with reductions in inflammatory lipids, increases in antioxidant capacity of other lipids, and changes in platelet activation (3).
What is good for one may not be as beneficial for all, though. For example, in adults with low levels of frailty, sedentary time is not predictive of mortality, regardless of physical activity level (4). Sitting more if you are already frail likely just increases frailty and mortality risk, which is not surprising. Along the same lines, being less fit matters in how you respond to breaking up sedentary time. Middle-aged adults with low levels of cardiorespiratory fitness gained the most metabolic benefit from breaking prolonged sitting with regular bouts of light walking, which included five minutes of light walking every 30 minutes over a 7-hour research period (5). If you’re already very fit, adding in some light walking breaks during the day is not going to have as much of an effect—again not surprising.
For in adolescents in school, reducing their sitting time (both in total time and length of bouts) has been shown to improve their blood lipid profiles and cognitive function. A “typical” day (65% of the time spent sitting with two sitting bouts >20 minutes) was compared with a simulated “reduced sitting” day (sitting 50% less with no bouts >20 minutes (6). Can teens stand to improve their health this week? Again, it cannot hurt to break up sedentary time, so why not do it? More recess breaks for teens would be good—and for everyone else for that matter.
All is not lost for people with limited mobility or no ability to engage in weight-bearing activities. Including short bouts of arm ergometry (five minutes of upper body work only every 30 minutes) during prolonged sitting attenuates postprandial glycemia (following two separate meals) when done by obese individuals at high risk of developing type 2 diabetes, even though they remain seated (7). People who cannot walk or stand can, therefore, break up their sedentary time in other ways that can also be metabolically beneficial.
As for other health benefits, breaking up sedentary time is associated with a lower risk of certain types of cancer. In a recent meta-analysis, prolonged television viewing, occupational sitting time, and total sitting time were all associated with increased risks of colorectal cancer in adults (8), which is the most common type after breast/prostate and lung cancers. That study reported a dose-response effect as well, suggesting that both prolonged total sitting time and greater total daily sitting time (2 hours) were associated with a significantly higher risk of colorectal cancer.
In summary, even just the most recent evidence is convincing enough that prolonged sitting is bad for you, and many more studies published similar results in prior years. Is sitting as bad as smoking, though? That remains to be proven. However, you really cannot argue with a recent international consensus statement on sedentary time in older people (9). It states, “Sedentary time is a modifiable determinant of poor health, and in older adults, reducing sedentary time may be an important first step in adopting and maintaining a more active lifestyle.” In fact, the best advice may simply be to consider the whole spectrum of physical activity, from sedentary behavior through to structured exercise (10). Putting yourself anywhere onto that spectrum is definitely better than sitting through the rest of your (shortened) life.
1. Larsen RN, Dempsey PC, Dillon F, Grace M, Kingwell BA, Owen N, Dunstan DW: Does the type of activity "break" from prolonged sitting differentially impact on postprandial blood glucose reductions? An exploratory analysis. Appl Physiol Nutr Metab 2017;42:897-900. doi: 810.1139/apnm-2016-0642. Epub 2017 Mar 1124.
2. Dempsey PC, Larsen RN, Sethi P, Sacre JW, Straznicky NE, Cohen ND, Cerin E, Lambert GW, Owen N, Kingwell BA, Dunstan DW: Benefits for type 2 diabetes of interrupting prolonged sitting with brief bouts of light walking or simple resistance activities. Diabetes Care 2016;39:964-972
3. Grace MS, Dempsey PC, Sethi P, Mundra PA, Mellett NA, Weir JM, Owen N, Dunstan DW, Meikle PJ, Kingwell BA: Breaking Up Prolonged Sitting Alters the Postprandial Plasma Lipidomic Profile of Adults With Type 2 Diabetes. J Clin Endocrinol Metab 2017;102:1991-1999. doi: 1910.1210/jc.2016-3926.
4. Theou O, Blodgett JM, Godin J, Rockwood K: Association between sedentary time and mortality across levels of frailty. CMAJ 2017;189:E1056-E1064. doi: 1010.1503/cmaj.161034.
5. McCarthy M, Edwardson CL, Davies MJ, Henson J, Bodicoat DH, Khunti K, Dunstan DW, King JA, Yates T: Fitness Moderates Glycemic Responses to Sitting and Light Activity Breaks. Med Sci Sports Exerc 2017;8:0000000000001338
6. Penning A, Okely AD, Trost SG, Salmon J, Cliff DP, Batterham M, Howard S, Parrish AM: Acute effects of reducing sitting time in adolescents: a randomized cross-over study. BMC Public Health 2017;17:657. doi: 610.1186/s12889-12017-14660-12886.
7. McCarthy M, Edwardson CL, Davies MJ, Henson J, Rowlands A, King JA, Bodicoat DH, Khunti K, Yates T: Breaking up sedentary time with seated upper body activity can regulate metabolic health in obese high-risk adults: A randomized crossover trial. Diabetes Obes Metab 2017;23:13016
8. Ma P, Yao Y, Sun W, Dai S, Zhou C: Daily sedentary time and its association with risk for colorectal cancer in adults: A dose-response meta-analysis of prospective cohort studies. Medicine (Baltimore) 2017;96:e7049. doi: 7010.1097/MD.0000000000007049.
9. Dogra S, Ashe MC, Biddle SJH, Brown WJ, Buman MP, Chastin S, Gardiner PA, Inoue S, Jefferis BJ, Oka K, Owen N, Sardinha LB, Skelton DA, Sugiyama T, Copeland JL: Sedentary time in older men and women: an international consensus statement and research priorities. Br J Sports Med 2017;19:2016-097209
10. Dempsey PC, Grace MS, Dunstan DW: Adding exercise or subtracting sitting time for glycaemic control: where do we stand? Diabetologia 2017;60:390-394. doi: 310.1007/s00125-00016-04180-00124. Epub 02016 Dec 00112.