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Sitting comfortably? How sitting is affecting our health

A growing body of evidence is pointing to the health risks associated with sedentary behaviours, and in particular risks associated with prolonged periods of sitting, independent of other physical activities.

While we have known for some time that regular physical activity is important to good health and that sedentary lifestyles are detrimental, what the emerging body of evidence is now suggesting is that periods of prolonged sitting can have negative health consequences even where people are meeting recommended exercise guidelines and maintaining a healthy body weight. In other words, undertaking the recommended 30 minutes of moderate to vigorous physical exercise each day, and keeping weight within healthy limits, may not be sufficient to maintain health, if people are also subject to long periods of sitting.

Four recent studies highlight this body of research. This VicHealth study summarises some of this recent research which together point to associations between time spent sitting and premature mortality, cardiovascular disease, elevated levels of insulin, blood glucose and blood pressure, and even mental illness. The study also points to the increase in sedentary work activities, with the advent of computerisation and the internet.

The Archives of Internal Medicine recently published a detailed analysis of survey data from those aged 45 or older in NSW and subsequent mortality data. The study found that prolonged sitting was responsible for 6.9% of all deaths among over 45s, independent of other risk factors, including body mass index (BMI).

A recent BMJ Open study which analysed data from the US National Health and Nutrition Examination Survey (NHANES) indicated that reducing sitting to under 3 hours a day would add an extra two years to life expectancy. This echoes an earlier Australian study on the effects of TV viewing on life expectancy, which found that the amount of TV watched in Australia had reduced life expectancy by 1.8 years for men, and 1.5 years for women.

How does prolonged sitting damage our health? The mechanism by which sedentary behaviour adversely impacts on the body is thought to be due to how it interferes with the body's metabolic functions, which regulate our insulin and cholesterol levels. Elevated insulin and cholesterol levels are linked to metabolic syndrome, heart disease and diabetes. While standing requires the muscles to constantly contract in order to balance the body, such preventive muscle activity is absent while sitting. Deep vein thrombosis (DVT) is another risk of prolonged sitting.

The policy implications of this research if substantiated by future studies, is potentially significant. Sitting for prolonged periods is a dominant feature of modern office work, but also it is a reality for transport workers such as bus, taxi and truck drivers, and airline pilots. Commuters in cars or on public transport often face long periods of sitting when travelling to and from work. Students routinely spend several hours a day sitting in class or studying, and our leisure time is also increasingly sedentary, watching TV, playing computer games, reading or updating our social media profiles.

More research will be needed to substantiate and deepen our understanding of the negative impact of sedentary behaviours, determine safe levels of sitting periods and develop appropriate interventions. But the VicHealth study suggests even simple interventions such as standing up for short breaks, can be beneficial. The VicHealth study also identified a number of other potential workplace interventions. These include redesigning workplaces to accommodate stand-sit desks, embedding regular microbreaks into work practices or prompting workers to stand/move via electronic reminders, conducting stand up meetings, adopting workplace wide exercise programs and introducing postural aids such as stretching against elastic bands, but not all will be practical for all situations.

Given sedentary activities are also increasingly dominating our leisure time as well as our work time, such workplace interventions may become increasingly important to maintain health. Although longer term benefits such as increased productivity may later flow if such interventions are adopted, encouraging employers to introduce these may not be straightforward. In some cases, significant re-design of work practices and work places may be required, at some cost. But if the future body of evidence continues to causally link prolonged sitting with adverse health outcomes, and employers fail to act to protect workers from these adverse health outcomes, then the risk of litigation will become a distinct possibility.

Therefore, determining optimal sitting times and appropriate low-cost interventions will need to be a focus of future research.