The act of sitting dominates modern North American culture. Our physical, economic and social environments have shifted rapidly over the last several decades which is apparent when considering the context in which we live on a daily basis. Sitting knows no environmental boundaries as we find ourselves on our haunches while in domestic settings (eating, using the washroom, etc), during leisure time (reading, TV, etc.), for many in the workplace, commuting any distance we determine to be an inconvenience to walk, etc.
While sitting is a seemingly innocuous activity, prolonged sitting can wreak havoc on our bodies. You may have heard the saying "sitting is the new smoking". How did this saying come about? An American study performed in 2011 estimated that after the age of 25, there is an estimated 22 minute reduction in life expectancy for every hour of TV watched. Ironically, 22 minutes is about the length of commercial interruptions for your favorite 1-hour TV show. When comparing this statistic to one commonly cited regarding cigarette smoking (an estimated reduction in life expectancy by 11 minutes per cigarette), it appears that prolonged sitting may be just as bad or worse for your health!
Prolonged sedentary behaviour (sitting being one of the biggest offenders) can lead to suppression of an enzyme called skeletal muscle lipoprotein lipase, or LPL for short. This enzyme is responsible for the uptake of triglycerides (the main constituent of fats and oils) and their further breakdown so that fatty acids may be used as energy. This enzyme is also responsible for producing the key components needed for the creation of HDL which is commonly known as the "good cholesterol".
An inflammatory marker called CRP has been found to be up to 3 times higher in those spending more than 4 hours of screen time per day (time spent in front of a TV, computer, etc.). In an American study in 2011, CRP was the strongest predictor for cardiovascular disease and was equally predictive alone compared to 3 other combined markers including BMI (body mass index), HDL ("good cholesterol"), and total cholesterol.
An Australian study (Australian Diabetes, Obesity and Lifestyle Study) revealed that self-reported TV time was positively associated with the presence of metabolic syndrome and undiagnosed abnormal glucose (sugar) metabolism which is seen in pre-diabetic and diabetic individuals. This same study also found that screen time over a five year period was able to significantly predict adverse changes in waist circumference in both men and women. Over this same five year period, cardiometabolic risk scores were also associated with screen time for women only.
What's worse is that the associations found in this Australian study accounted for moderate to vigorous intensity activity and prior waist circumference, meaning that the results of the study were due to screen time irrespective of these other factors.
The negative effects mentioned above are not all encompassing for prolonged sitting. There are other physiological changes that have been noted with excessive sedentary behaviour which I have not discussed. They've been omitted not because they're unimportant but because I intended for this to be a short post that is now becoming long-winded.
In my next post I'll discuss some additional information from these studies and some actionable bits of info that can help you decrease the potential harm of sitting/sedentary behaviour.