10th July 2012 - Cutting the amount of time we spend sitting to less than three hours a day could extend life expectancy by two years, scientists calculate.
Similarly, they say that watching TV for less than two hours a day might add an extra 1.4 years onto our lives.
The authors caution that people should not assume that their findings prove that someone who spends much of the day sitting can expect to live two or 1.4 years less, but that a sedentary lifestyle is detrimental to health.
"Sitting is a risk factor, not a disease," says co-author Peter Katzmarzyk, a population science expert at Louisiana State University System in the US. He tells us: "It's comparable to obesity, and it's almost to the level of smoking."
The researchers used data from the National Health and Nutrition Examination Survey (NHANES) for 2005-2006 and 2009-2010 to see how much time US adults spent watching TV and sitting down. They also analysed five studies of 167,000 adults that looked at sitting time and deaths from all causes.
They estimated the theoretical effects that a factor such as sitting would have at a population level.
The results indicate that cutting the amount of time spent sitting down every day to less than three hours would add an extra two years to life expectancy. Similarly, restricting time spent watching TV to less than two hours daily would extend life expectancy by an extra 1.38 years.
The authors say that further studies will be needed before recommendations could be made on how long people can safely stay on the sofa each day. However, they say we could take immediate steps to help improve our health. "We sit to eat and don't tend to stand up a whole lot," says Peter Katzmarzyk. "We need to turn that around and engineer sitting out of our lives."
Current guidelines in the UK say adults should limit the time they spend sitting for long periods and aim for at least two-and-a-half hours of moderate activity each week spread over a minimum of five days. In addition they should also undertake physical activity to improve muscle strength on at least two days a week.'
Natasha Stewart, senior cardiac nurse at the British Heart Foundation, said in a statement: "This research only suggests a causal association between sedentary behaviour and a shorter life expectancy. It also used American data so we'd need to see more research to understand what it means for the UK population.
"However, it does highlight what we already know about sedentary behaviour being a risk factor for developing heart disease. And recent UK guidelines suggested we should all minimise the time we spend sitting down.
"We all need to be regularly active to keep our hearts healthy. So whether it's by walking to the local shop rather than driving, or playing sport rather than watching it on TV, there are lots of ways to be more active and improve your health."
'Sedentary behaviour and life expectancy in the USA: a cause-deleted life table analysis', Peter T Katzmarzyk, I-Min Lee, BMJ Open 2012.
Peter Katzmarzyk, PhD, associate executive director, population science, Pennington Biomedical Research Center, Louisiana State University System, Baton Rouge, US.
'Too much TV is bad for your heart', WebMD Health News, 12th January 2010.
'Physical activity guidelines for adults (19-64 years)', Department of Health.
British Heart Foundation.
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