An extensive review of previous studies looks at the health implications associated with prolonged sitting, and the behaviours that may offset these negative effects. Review by Dr Mike Climstein PhD and Dr Joe Walsh PhD
THE QUICK READ
- The average adult spends a high proportion of their day in a sedentary, seated position.
- A comprehensive review of nine extensive studies found that the more time people spent sitting down, the greater their risk of heart disease and diabetes.
- Exercise was found to reduce the risk of these health conditions in people who sat for high amounts of time.
- Higher blood pressure, higher elevated cholesterol levels, and back and shoulder pain were also associated with large amounts of sedentary time.
Title: Sitting time and risk of cardiovascular disease and diabetes: A systematic review and meta-analysis
Authors: Dr Bailey and colleagues. (Institute for Sport and Physical Activity Research, School of Sport Science and Physical Activity, University of Bedfordshire, United Kingdom)
Source: American Journal of Preventive Medicine. 57(3):408-416.
Introduction: Many, many years ago I used to compete as an Olympic lifter, and when pushing the limits, I ended up herniating my L5/S1 disc and subsequently had chymopapain injection, which allowed me to continue lifting… somewhat. My low back could no longer tolerate the ballistic pulls of the snatch and clean and jerk lifts, but the less dynamic lifts in powerlifting were no problem.
The surgeon told me that after the surgery my low back would lose flexibility. Little did I know that a loss of low back flexibility was not the only problem, and I also experienced minor low back pain when I would sit for prolonged periods of time.
When I measured how much sitting I was doing at work, and then at home on the computer and watching television, I was absolutely shocked! A study published in the Journal of the American Medical Association (Pandey et al., JAMA 2016) reported that sitting 12.5 hours per day increased your risk of heart disease by 14% compared to those that only sat for 2.5 hours per day. Now I’m no longer wondering why my colleagues at the university have variable height desks that they can stand or sit at.
In the late 2000’s a number of physiologists began investigations into what was called ‘inactive physiology’ or ‘sitting physiology’ and this began the interest in the deleterious effects of sitting on health. Recently, Dr Bailey and his colleagues in the UK conducted a review of the literature involving sitting and its associated development of chronic diseases. Initially, they reported that the average adult spends up to 60% of their waking time in sedentary behaviour, which equated to over 8 hours per day. They conducted an electronic search of the major databases (PubMed, Web of Science, BASE, MEDLINE and ScienceDirect) of available research from 1989 to the present day on studies that followed up on individuals 18 years of age and older who were initially healthy, and their total sitting time was measured.
Results: Initially, over 4,000 articles were identified, however only nine with over 224,000 participants were used in this literature review. The studies had follow-up times that ranged from 2.7 to 13 years. The higher total daily sitting time was found to be associated with a 29% increased risk of cardiovascular disease and 13% increased risk for type 2 diabetes mellitus. The authors explain that this increased risk is attributed to a number of physiological mechanisms, which result in higher levels of lipids (i.e. cholesterol), blood glucose and insulin. They also report that prolonged sitting may result in vascular dysfunction and hence atherosclerosis.
The thresholds for determining increased risk varied among the studies, with some studies having the highest sitting threshold at > 7.1 hours per day up to > 16.0 hours per day. The lowest sitting group thresholds also varied from < 4 hours per day to < 8 hours per day.
The authors did include information that these deleterious effects of prolonged sitting on increased risk for cardiovascular disease and type 2 diabetes mellitus has been shown to be reduced in individuals who complete 60 to 75 minutes of moderate-intensity exercise per day.
Pros: This was a good study, however additional research is needed in sitting physiology to determine absolute thresholds for a number of chronic diseases and what amount (and intensity) of physical activity/exercise is needed to counteract the deleterious effects of prolonged sitting.
Safe Work Australia recommends a number of strategies for combatting the deleterious effects of prolonged occupational sitting, including breaking up prolonged sitting by either standing or walking, or a combination of standing and walking. Researchers have recommended standing for 15 to 30 minutes per hour to attain the health benefits. The Figure above from Safe Work Australia (Safe Work Australia, 2019) displays examples of how the work day can be made healthier by interspersing standing and walking in an otherwise sedentary day.
Research by Daneshmandi et al., (2017) reported that office workers sitting for 6.5 hours out of an 8-hour shift demonstrated 6.3% higher blood pressure and 11.2% higher elevated cholesterol, and that over 50% had low back and shoulder problems. A study by Suliga and colleagues (2018) reported that sitting for more than 6 hours per day resulted in an average 14% increased risk for metabolic syndrome.
Cons: It would be beneficial for researchers to conduct a review on available research for a number of chronic diseases and conditions and the doses of exercise needed to offset the increased risk.
Bailey, D., Hewson, D., Champion, R., & Sayegh, S. (2019). Sitting Time and Risk of Cardiovascular Disease and Diabetes: A Systematic Review and Meta-Analysis. American Journal of Preventive Medicine. 57(3):408-416.
Ekelund, U., Steene-Johannessen et al., (2016). 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. 388(10051):1302-1310.
Daneshmandi, H., Choobienh, A., Ghaem, H., & Karimi, M. (2017). Adverse Effects of Prolonged Sitting Behavior on the General Health of Office Workers. Journal of Lifestyle Medicine. 7(2):69-75.
Safe Work Australia (2019, July 29th). Sitting and standing. Retrieved from https://www.safeworkaustralia.gov.au/sedentary#ways-to-reduce-occupational-sitting (2019, 26th August).
Suliga, E., Ciesla, E., Rebak, D., Koziel, D., & Gluszek, S. (2018). Relationship Between Sitting Time, Physical Activity, and Metabolic Syndrome Among Adults Depending on Body Mass Index (BMI). Medical Science Monitor. 24: 7633-7645.
Dr Mike Climstein, PhD FASMF FACSM FAAESS AEP
Dr Climstein is one of Australia’s leading Accredited Exercise Physiologists. He is a faculty member in Clinical Exercise Physiology, Sport & Exercise Science at Southern Cross University (Gold Coast). email@example.com
Dr Joe Walsh
Joe is a sport and exercise scientist. As well as working for Charles Darwin and Bond Universities, he is a director of Fitness Clinic in Five Dock, Sydney. fitnessclinic.com.au