While watching Netflix, a film, or sports after a day at work can be a desirable way to relax, a thorough meta-analysis of sitting and physical activity schedules among people found that 3 hours of time sitting in front of a TV increased risk for death from all causes, regardless of time spent exercising, and number of days per week in which exercise is undertaken.
The meta-analysis, which is sort of like a study of studies, found 13 randomized controlled trials involving 1 million people.
It looked at the relations between the risks of death from all causes, as well as cardiovascular disease mortality, and cancers of the breast, colon, and colon-rectum, with average hours spent sitting, and frequency of exercise.
The exercise was measured in Metabolic Equivalent of Task in hours, which is a scale one may have seen on gym equipment, and which measures the amount of energy expended during the time one uses the equipment.
Divided into quarters, and compared with the most active quarter, who performed 35.5 MET hours per week, which is the equivalent of burning 21,000 calories while running 5 miles an hour for a 160-pound person, all other groups saw increased risks of death during the follow-up on the study, with the lowest quarter at a 59% increased risk of death.
One of the most striking findings was that only this extreme level of physical activity was enough to remove the noticeable increase in the risk of death for those who spent 3 hours or more watching TV, despite the fact that there was no increase in risk of death if normal sitting time was higher than 8 hours in these super-active people. Something about the TV element decreased survival rate where regular sitting did not.
“High levels of moderate intensity physical activity (i.e. about 60–75 min per day) seem to eliminate the increased risk of death associated with high sitting time,” the authors write. “However, this high activity level attenuates, but does not eliminate the increased risk associated with high TV-viewing time”.
“Watching TV for 3 hours or more per day was associated with increased mortality regardless of physical activity, except in the most active quartile, where mortality was significantly increased only in people who watched TV for 5 hours per day or more”.
People who managed 16 MET hours of physical activity, which is above the recommendations for weekly-physical activity for the World Health Organization, the CDC, and the NIH as well as many international health advisory bodies, were still vulnerable to this increase in risk of death from all causes, certain cancers, and cardiovascular disease.