Sit for Less than Three Hours a Day, Live Two Years Longer

Spending extended periods of time sitting or just watching TV has been linked to poor health and conditions like diabetes and death from heart disease or stroke by several studies. Now a new study published in the online journal BMJ Open indicates that it is possible to extend life expectancy by as much as two years if the daily time spent sitting is cut down to below three hours. The research has also found that if we watch TV for less than two hours a day, we can add another 1.4 years to our expected life.



Conducted by researchers from the Louisiana State University in the US, the study utilised data collected from the National Health and Nutrition Examination Survey (NHANES) for the years 2005-’06 and 2009-’10. NHANES conducts annual surveys of large representative samples of the US population and collects data on various aspects of their lifestyle and health. Using this data, the researchers derived the amount of time spent by an average US adult in front of the TV and on sitting down daily.



Once they had this data in hand, they went through the MEDLINE research database to analyse studies related to sitting time and deaths from all causes. Taking five relevant studies covering close to 167,000 adults, the researchers pooled the relative risk data and then reanalysed it all by taking age and sex into consideration. The combination of these data and the figures arrived at from the NHANES data provided them the base to draw up a population attributable fraction (PAF).



PAF represents the estimated theoretical effects of a particular risk factor on the entire population and allowed the researchers to calculate the number of deaths linked to time spent sitting down. The researchers found that PAFs on account of sitting time and TV viewing for deaths from all causes were respectively 27% and 19%. Life table analyses for the population indicated that if the time spent sitting down every day is cut down to under three hours, it is possible to increase life expectancy by two years. An additional 1.38 years can be added to the life expectancy if TV viewing time was reduced to under two hours daily.



While the findings are clear, the authors also emphasise that they have carried out an analysis that only provides a causal association between sitting down and life expectancy; their study does not prove there is one. However, there is enough evidence provided by other studies that a sedentary lifestyle does have a negative effect on health. The add another word of caution for those living sedentary lifestyles; just by cutting down on sitting or TV viewing time would not be enough to increase their life expectancy by two years or 1.4 years in comparison to active people.



The researchers have this to say about their analysis, “The results of this study indicate that extended sitting time and TV viewing may have the potential to reduce life expectancy in the USA. Given that the results from objective monitoring of sedentary time in NHANES has indicated that adults spend an average of 55% of their day engaged in sedentary pursuits, a significant shift in behaviour change at the population level is required to make demonstrable improvements in life expectancy.”

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