Two new studies about the perils of sitting may have spoiled our TV viewing pleasures. The research,published in separate medical journals this month,adds to a growing scientific consensus that the more time someone spends sitting,especially in front of the TV,the shorter and less robust his or her life may be.
To reach that conclusion,the authors of one of the studies,published in the October issue of The British Journal of Sports Medicine,turned to data from the Australian Diabetes,Obesity and Lifestyle Study,a large,continuing survey of the health habits of almost 12,000 Australian adults.
The survey asked respondents how many hours per day in the previous week they had spent sitting in front of the television.
Watching TV is not,of course,in and of itself hazardous. But TV viewing time is a useful,if somewhat imprecise,marker of how much someone is engaging in so-called sedentary behaviour.
According to the survey data,in 2008,the year that the researchers chose as their benchmark,Australian adults viewed a collective 9.8 billion hours of TV. The findings: Every single hour of TV watched after the age of 25 reduces the viewers life expectancy by 21.8 minutes.
By comparison,smoking a single cigarette reduces life expectancy by about 11 minutes,the authors said.
Looking more broadly,they concluded that an adult who spends an average of six hours a day watching TV over the course of a lifetime can expect to live 4.8 years fewer than a person who does not watch TV. The results are true,the study says,even for people who exercise regularly.
These rather unnerving results jibe with those of another new study of sitting. Published this week in the journal Diabetologia,its authors reviewed data from 18 studies involving 794,577 people. Many of the studies measured full-day sitting time,covering not only hours in front of the television,but also time spent in a chair at work.
Together,those hours consumed a majority of a persons life. The average adult spends 50 to 70 per cent of their time sitting, the authors report.
The researchers then cross-referenced sitting time with health outcomes,and found that those people with the highest sedentary behavior, meaning those who sat the most,had a 112 per cent increase in their relative risk of developing diabetes; a 147 per cent increase in their risk for cardiovascular disease; and a 49 per cent greater risk of dying prematurely even if they regularly exercised.
Why a seemingly blameless activity like sitting should be detrimental to health,even for those of us who work out,is not fully understood,although it is assiduously being studied at many labs.
One partial explanation,however,is obvious.
The most striking feature of prolonged sitting is the absence of skeletal muscle contractions,particularly in the very large muscles of the lower limbs, says David W Dunstan,a professor at the Baker IDI Heart and Diabetes Institute in Australia,senior author of the Australian study,and a pioneer in the study of sedentary behaviour.
When muscles dont contract,they require less fuel,and the surplus,in the form of blood sugar,accumulates in the bloodstream,contributing to diabetes risk and other health concerns.