Are you sitting comfortably? Well, you had better stand up. Sitting is the latest health hazard, according to a study published this week, showing that being sedentary for hours at a time increases your risk of diabetes, heart disease and premature death.
The research, from the University of Leicester and published in the journal Diabetologia, combined the results of 18 studies and nearly 800,000 people. It found that prolonged sitting doubled the risk of diabetes and heart disease, and that the risk wasn't eliminated for those people who took regular exercise. Sitting is a low energy activity and it may be risky because it makes our bodies think we are in energy storage mode. This makes our bodies resistant to insulin (which mops up glucose), increasing the level of glucose in the blood and reducing levels of good cholesterols while increasing levels of bad ones. All of these changes increase the risk of obesity, diabetes and heart disease.
The authors of the Diabetologia study say that on average adults spend 50% to 70% of their time sitting down, either at work, watching television or using the computer. These activities use up a measly one MET (metabolic equivalent) of energy expenditure. If you walk you use four times as much energy as when you sit.
This study confirms findings from other research. An Australian paper in the Archives of Internal Medicine of more than 200,000 people aged 45 or over found that those who sat for 11 or more hours a day had a 40% increase in risk of dying over the next three years, compared with those who sat for only four hours a day. The study took into account how healthy they were, as well as their levels of physical activity and weight.
The relationship between sitting and ill health has spawned an area of study called inactivity research. Prolonged inactivity has been known for decades to contribute to back pain and obesity; now it seems we can blame it for killing people prematurely. But since most sitting occurs at work, is there anything you can do to reduce it?
The solution
What you can do to help will depend on your workplace. If you can, set an alarm to make sure you get up once an hour and walk briskly somewhere. Instead of emailing someone several desks away, speak to them in person. Stand up when taking a phone call – it uses more calories than sitting. Shun the lift and take the stairs. In meetings get up and walk around the room. There are even desks attached to treadmills available, that allow people to walk slowly while working at their desks.
After work, try not to spend most of the evening watching television. Another Australian study, in the October issue of The British Journal of Sports Medicine, suggests that each hour of television watched after the age of 25 reduces life expectancy by 21.8 minutes.
COMMENT
I wouldn't say that it is "the latest health hazard". In the last 10 years or so, especially the last 5 years, there is a growing body of research on the effects of sedentary behaviour, including sitting; sedentary behaviour is defined as activity whose energy cost is between 1-1.5 METs, basically sitting, lying down, watching TV, posting comments on CiF. It appears that sedentary behaviour's deleterious effects might affect from a different mechanism from the positive effects of physical activity. Even in people with high levels of leisure time physical activity, sitting time appears to be strongly associated with all cause mortality. The currently postulated mechanism is that lipoprotein lipase activity is (drastically) reduced in deep postural oxidative (slow twitch) muscles as a result of sedentary behaviour, and that (physical) activity will increase LPL activity, but NOT in those deep postural oxidative muscles, but rather in (superficial) glycolytic muscles.
For those who want to read up more on the issue, other than the new study and the study on sedentary behaviour on all cause mortality in Aussie, see for example:
Katzmarzyk PT, Church TS, Craig CL, Bouchard C. Sitting time and mortality from all causes, cardiovascular disease, and cancer. Med Sci Sports Exerc. 2009 May;41(5):998-1005.
Saunders TJ, Larouche R, Colley RC, Tremblay MS. Acute sedentary behaviour and markers of cardiometabolic risk: a systematic review of intervention studies. J Nutr Metab. 2012;2012:712435. Epub 2012 Jun 17.
Lynch BM.Sedentary behavior and cancer: a systematic review of the literature and proposed biological mechanisms.Cancer Epidemiol Biomarkers Prev. 2010 Nov;19(11):2691-709. Epub 2010 Sep 10
And a paper that contains a pretty good review of the possible mechanisms:
Hamilton MT, Healy GN, Dunstan DW, Zderic TW, Owen N. Too Little Exercise and Too Much Sitting: Inactivity Physiology and the Need for New Recommendations on Sedentary Behavior. Curr Cardiovasc Risk Rep. 2008 Jul;2(4):292-298.
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