How bad is sitting for a long time?

How bad is sitting for a long time?

Sitting for prolonged period can affect health even in those who follow the physical activity guidelines. It is still worse in those who do not follow the guidelines for physical activity. In fact, sitting for more than five hours a day has been considered to carry a cardiovascular risk equivalent to that of smoking. But heaving smoking of more than 40 cigarettes per day carries a relative risk of death of 4.08, while sedentary behaviour has a hazard ratio of 1.22 [1]. So sitting cannot be considered as ‘new smoking’ though sedentary behaviour is not desirable. Sitting time would include sitting at work, television viewing time and similar static leisure activities as well as time spent traveling in automobiles. Any situation with energy expenditure of 1.5 metabolic equivalents (METs) or less like sitting, reclining or lying posture has been called sedentary behaviour [1].

An interesting study evaluated the physical activity, sedentary time and cardiometabolic health in heavy goods vehicle drivers [2]. It involved 329 heavy goods vehicle drivers from United Kingdom. 88.1% of the drivers were overweight or had obesity. Pre-diabetes or diabetes was found in 11.9% and 28.3% had hypertension. Elevated low density lipoprotein cholesterol (LDL) was noted in 83.6%. The drivers had 12 hours/day of sitting on workdays. They had 1.7 hours/day of light physical activity and 9.8 minutes/day of moderate to vigorous physical activity. This should be considered in the background of the recommended minimum of 30 minutes of moderate to vigorous physical activity per day.

A study using computed tomographic coronary angiography (CT-CAG) enrolled 203 subjects at annual medical check ups, with mean age of 57.6 years [3]. Sitting time was categorized as short if less than 5 hours/day, moderate if between 5 to 9 hours and long if 10 hours or more. Parameters analysed were coronary calcium score, plaque characteristics and severity of coronary artery stenosis. Increased sitting was independently associated with mixed plaque even after adjusting for age, gender, comorbidities, body mass index and lipid profiles. Higher coronary segment involvement score and coronary segment stenosis score were noted in those with longer sitting time.

A systematic review with meta analysis found 47 studies assessing sedentary behaviour in adults adjusted for physical activity [4]. They concluded that prolonged sedentary time was independently associated with deleterious health outcomes regardless of physical activity. The outcomes evaluated were cardiovascular disease, diabetes, cancer and all-cause mortality. Significant hazard ratios were documented for all-cause mortality, cardiovascular disease mortality, incidence of cardiovascular disease, cancer mortality and incidence of type 2 diabetes mellitus. The effects were generally more pronounced at lower levels of physical activity than at higher levels.

Another meta analysis of nine prospective cohort studies with 720 425 unique participants with a median follow up of 11 years documented 25 769 unique cardiovascular events [5]. They found a non-linear relationship between sedentary time and risk for cardiovascular disease with increased risk only at very high levels. Highest sedentary time category in their analysis had median sedentary time of 12.5 hours/day while the lowest sedentary time category had median 2.5 hour/day.

An earlier meta analysis included six studies with data from 595,086 adults with 29,162 deaths over 3,565,569 person-years of follow-up [6]. They also found that the association between daily total sitting time and all-cause mortality was non linear. Their model estimated a 34% higher mortality risk for adults sitting 10 hours/day, after taking physical activity into account. They also concluded that moderate to vigorous physical activity appeared to attenuate the hazardous association of high amounts of daily sitting time with all-cause mortality.

Sitting for a long time can lead to obesity, mostly abdominal, with increased blood pressure, chance for type 2 diabetes mellitus and dyslipidemia constituting metabolic syndrome. Standing desks at work are being promoted to avoid prolonged sitting. This is in addition to methods of enhancing physical activity at work like using stairs instead of lift and having the parking slot a bit away to mandate walking. Prolonged sitting can also be linked to back pain, varicose veins and even deep vein thrombosis in situations like long haul flights. Working for long periods on a computer in an ergonomically unfavourable posture can get you pain in the neck as well.

Reference

1. Vallance JK, Gardiner PA, Lynch BM, D’Silva A, Boyle T, Taylor LM, Johnson ST, Buman MP, Owen N. Evaluating the Evidence on Sitting, Smoking, and Health: Is Sitting Really the New Smoking? Am J Public Health. 2018 Nov;108(11):1478-1482. doi: 10.2105/AJPH.2018.304649. Epub 2018 Sep 25. PMID: 30252516; PMCID: PMC6187798.
2. Ruettger K, Varela-Mato V, Chen YL, Edwardson CL, Guest A, Gilson ND, Gray LJ, Paine NJ, Sherry AP, Sayyah M, Yates T, King JA, Clemes SA. Physical Activity, Sedentary Time and Cardiometabolic Health in Heavy Goods Vehicle Drivers: A Cross-Sectional Analysis. J Occup Environ Med. 2022 Jan 19. doi: 10.1097/JOM.0000000000002484. Epub ahead of print. PMID: 35051962.
3. Lim SS, Huang CC, Hsu PF, Lin CC, Wang YJ, Ding YZ, Liou TL, Wang YW, Huang SS, Lu TM, Chen JW, Chan WL, Lin SJ, Leu HB. Prolonged sitting time links to subclinical atherosclerosis. J Chin Med Assoc. 2022 Jan 1;85(1):51-58. doi: 10.1097/JCMA.0000000000000672. PMID: 34861666.
4. Biswas A, Oh PI, Faulkner GE, Bajaj RR, Silver MA, Mitchell MS, Alter DA. Sedentary time and its association with risk for disease incidence, mortality, and hospitalization in adults: a systematic review and meta-analysis. Ann Intern Med. 2015 Jan 20;162(2):123-32. doi: 10.7326/M14-1651. Erratum in: Ann Intern Med. 2015 Sep 1;163(5):400. PMID: 25599350.
5. Pandey A, Salahuddin U, Garg S, Ayers C, Kulinski J, Anand V, Mayo H, Kumbhani DJ, de Lemos J, Berry JD. Continuous Dose-Response Association Between Sedentary Time and Risk for Cardiovascular Disease: A Meta-analysis. JAMA Cardiol. 2016 Aug 1;1(5):575-83. doi: 10.1001/jamacardio.2016.1567. PMID: 27434872.
6. Chau JY, Grunseit AC, Chey T, Stamatakis E, Brown WJ, Matthews CE, Bauman AE, van der Ploeg HP. Daily sitting time and all-cause mortality: a meta-analysis. PLoS One. 2013 Nov 13;8(11):e80000. doi: 10.1371/journal.pone.0080000. PMID: 24236168; PMCID: PMC3827429.