Restricting the amount of time spent sitting down each day to less than three hours could boost the life expectancy of US adults by as much as two years, research has found.
Reducing the number of hours spent watching TV to fewer than two every day could also extend life by nearly 1.4 years, the study published in the online journal BMJ Open said.
In carrying it out, researchers found evidence that adults spend an average of 55% of their day engaged in sedentary pursuits.
Several previous studies have linked extended periods spent sitting down and/or watching TV to poor health and death from heart disease or stroke.
In this latest study, researchers used data collected for the National Health and Nutrition Examination Survey (NHANES) for 2005/6 and 2009/10, to calculate the amount of time US adults spent watching TV and sitting down on a daily basis.
NHANES regularly surveys a large representative sample of the US population on various aspects of their health and lifestyle.
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They trawled the research database MEDLINE, looking for published studies on sitting time and deaths from all causes, and pooled the different relative risk data from the five relevant studies, involving almost 167,000 adults.
The database was then re-analysed, taking account of age and sex.
They combined these data and the NHANES figures to come up with an estimate of the theoretical effects of a risk factor to a population, rather than an individual level - to calculate the number of deaths associated with time spent sitting down.
They found that cutting the amount of time spent sitting down every day to under three hours would add an extra two years to life expectancy.
Similarly, restricting time spent watching TV to under two hours daily would extend life expectancy by an extra 1.38 years.
The authors said their analysis assumes a causal association rather than proving that there is one and added their findings should not be interpreted as meaning that someone who leads a more sedentary lifestyle can expect to live two or 1.4 years less than someone who is more active.
Further research will be required before recommendations on safe levels of sedentary behaviour can be made, they said.
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