The researchers used data collected for the National Health and Nutrition Examination Survey (NHANES) in order to determine how much time US adults spent sitting down and watching TV each day. In addition, they examined five published studies on sitting time and deaths from all causes. Combined, the five studies involved almost 167,000 adults.
Results from the five studies and the NHANES figures were then combined in order to come up with a population attributable fraction (PAF) - an estimate of the theoretical effects of a risk factor at a population, rather than an individual level - to calculate the number of deaths associated with time spent sitting down.
According to the researchers, the PAFs for deaths from all causes associated to sitting time was 27% and 19% for TV viewing.
The team found that individuals could live two years longer if they reduce the amount of time spent sitting to under three hours per day. In addition, they found that reducing the amount of time spent watching TV to under 2 hours per day would boost life expectancy by 1.38 years.
The researchers highlight that their study assumes a causal association rather than proving that there is one. However, they note that earlier studies have linked extended periods spent sitting down and/or watching TV to poor health, such as diabetes and death from heart disease/stroke.
Furthermore, they state that results of this study do not mean that someone who leads a more sedentary lifestyle can expect to live two or 1.4 years less than someone who is more active.
Ever since the 1950s, when TVs entered our living rooms, our lives have become more sedentary
The researchers explain:
"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 NHAHES has indicated that adults spend an average of 55% of their day engaged in sedentary pursuits, a significant shift in behavior change at the population level is required to make demonstrable improvements in life expectancy."
They conclude that more studies are needed before recommendations on safe levels of sedentary behavior can be made.