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The News That's Best Not to Take Sitting Down

Monday, 17 March 2014

By Brenton Wright

It has long been proposed that in order for people to maintain their health, they needed to perform at least 30 minutes of moderate intensity exercise per day to lower their risk of CVD.

It is widely accepted that this is the minimum amount of activity required and will suffice for a person who is generally sedentary, sedentary behaviour being defined as activities which have an energy expenditure similar to that of resting, such as sleeping, sitting, watching tv etc. (Bankoski, 2011).

I have recently come across a publication which compared prolonged sitting to smoking and drinking as high risk activity, and in a study of two hundred thousand people, 7% of the deaths were attributable to prolonged sitting, with a 40% higher risk of death compared to people who sat for 4 hours or less. (Taylor, 2012) Associate professor David Dunstan said there was no effect from intensity but merely from the physical movement. Commonwealth Bank in Sydney are trialling activity-based working, in which they don't have desks or landlines, and mostly walk around or have standing desks with staircases enhanced to encourage walking. (Taylor, 2012) http://www.abc.net.au/catalyst/stories/3568627.htm this is a link to their presentation

The multivariable model was stratified by age and includes race; education; income; marital status; smoking; family history of myocardial infarction; depression; alcohol intake; hours of sleep; intake of total calories, saturated fat, and fiber; and body mass index, and demonstrates the relationship between risk factors and activity with inactivity

(Andrea K. et al, 2013)


So it would appear that a large portion of the problem is not level of exercise but the level of inactivity. A higher percentage of time spent sedentary is associated a significantly greater likelihood of a metabolic syndrome, even after adjustments were made to account for physical activity, with a further increase in risk with fewer breaks from sedentary bouts and intensity during sedentary time. (Bankoski, 2011). A recent randomized trial showed that interrupting sitting with short bouts of light or moderate intensity activity lowers postprandial glucose and insulin levels in overweight adults (Andrea K. et al, 2013), one of the recommendations was 2 minute bouts of exercise every 20 minutes to lower the consequences of sedentary activity and postprandial hyperglycaemia. (Taylor, 2012) (David W. Dunstan, 2012)Postprandial is the period after a meal and hyperglycaemia means the high blood sugar levels.

CVD = cardiovascular disease HR = hazard ratio MET = metabolic equivalent task.

These blood sugar spikes are exacerbated by the consumption of high calorie meals which contain processed carbohydrates and saturated fats, when these spikes are repeated regularly, they have been associated with the progression of atherosclerotic indices, retinopathy, type 2 diabetes, cardiovascular events and death. Guidelines for cardiovascular health include minimizing the magnitude of postprandial hyperglycaemia (David W. Dunstan, 2012)

One of the main enzymes relating to the control of this is Lipoprotein Lipase (LPL) which has a key role in the production of HDL cholesterol (the good cholesterol) glucose transport and the regulation of triglyceride transport into muscle and fat tissue, which are two of the primary locations it is synthesized. Its production in muscles is very sensitive to physical activity of all intensities and is inhibited while remaining sedentary (Caren E. Smitha, 2009)

Ultimately, resolving the problem of inactivity requires a sustained change in individual daily activity and sedentary patterns. From a public health perspective, a reduction in sedentary behaviour may be easier than increasing physical activity because there are fewer restrictions (i.e. no need to change clothing or use special equipment), and can be easily attained with minimal burden to a person's time or financial resources. (Mark, et al., 2011). limit discretionary sitting time to no more than 2 hours/day, and to stand up and move after 30 minutes of uninterrupted sitting (this would be considered a break in sedentary time), for example, when watching TV or using a computer. (Neville Owen, 2011) The behaviours and contexts of primary concern are TV viewing and other screen-focused behaviours, prolonged sitting in the workplace, and time spent sitting in automobiles. One innovation I have come across which attempts to address this issue lies in an ergonomic style of chair, which simulates the posture of standing.



Andrea K. Chomistek, ScD, JoAnn E. Manson, MD, DrPH, Marcia L. Stefanick, PhD, Bing Lu, MD, DrPH, Megan Sands-Lincoln, PhD, Scott B. Going, PhD⋮, Lorena Garcia, PhD. (2013). Journal of american college of cardiology , Vol. 61, Issue. 23, 2346-2354.

Bankoski, A. M. (2011). Sedentary activity associated with metabolic syndrome independant of physical activvty. Diabetes care , vol. 34, no 2, pp.497-503.

Caren E. Smitha, D. K.-Q. (2009). Physical inactivity interacts with an endothelial lipase polymorphism to modulate high density lipoprotein cholesterol in the GOLDN study. Atherosclorosis , Vol. 206, Issue. 2, P. 500-504.

David W. Dunstan, P. B. (2012). Breaking Up Prolonged Sitting Reduces Postprandial Glucose and Insulin Responses. Diabetes Cre , Vol.35, p. 976-983.

Mark, T., Allana, L., Michelle, K., Travis, S., Richard, L., Rachel, C., et al. (2011). Systematic review of sedentary behaviour and health indicators in school-aged children and youth. Journal of bahavioural Nutrition and physical activity , Vol8, p. 98.

Neville Owen, P. T. (2011). Adults' Sedentary Behavior: Determinants and Interventions. American Journal of Preventive Medicine , Vol. 41, Issue. 2, p. 189-196.

Taylor, A. (2012, Ausgust 16). Catalyst. Retrieved October 28, 2013, from ABC television: Anja Taylor. 2012. Catahttp://www.abc.net.au/catalyst/stories/3568627.htm