On average, 80% of American adults watch 3.5 hours of television per day and multiple observational studies have demonstrated a link between TV viewing and poorer health. In this new study published in the December issue of the American Journal of Preventive Medicine, investigators reported an association between increasing hours of television viewing per day and increasing risk of death from most of the major causes of death in the United States.

Virtually all Americans (92%) have a television at home and watching TV consumes more than half of their available leisure time, potentially displacing more physical activities. Previous studies had reported a relationship between TV viewing and elevated risk of death from cancer and cardiovascular disease. In this study, researchers at the National Cancer Institute looked at more than 221,000 individuals aged 50-71 years old who were free of chronic disease at study entry. They confirmed the association for higher mortality risk from cancer and heart disease. In addition, they identified new associations with higher risk of death from most of the leading causes of death in the U.S., such as, diabetes, influenza/pneumonia, Parkinson's disease, and liver disease.

"We know that television viewing is the most prevalent leisure-time sedentary behavior and our working hypothesis is that it is an indicator of overall physical inactivity. In this context, our results fit within a growing body of research indicating that too much sitting can have many different adverse health effects," explained lead investigator Sarah K. Keadle, PhD, MPH, Cancer Prevention Fellow, Nutritional Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute.

Dr. Keadle cautioned that although each of the associations observed have plausible biological mechanisms, several associations are being reported for the first time and additional research is needed to replicate these findings and to understand the associations more completely. "Our study has generated new clues about the role of sedentary behavior and health and we hope that it will spur additional research."

The study found that compared to those who watched less than one hour per day, individuals who reported watching 3-4 hours of television watching per day were 15% more likely to die from any cause; those who watched 7 or more hours were 47% more likely to die over the study period. Risk began to increase at 3-4 hours per day for most causes they examined. The investigators took a number of other factors into consideration that might explain the associations observed, such as caloric and alcohol intake, smoking, and the health status of the population, but when they controlled for these factors in statistical models, the associations remained.

Another important finding of the study is that the detrimental effects of TV viewing extended to both active and inactive individuals, "Although we found that exercise did not fully eliminate risks associated with prolonged television viewing, certainly for those who want to reduce their sedentary television viewing, exercise should be the first choice to replace that previously inactive time," said Dr. Keadle.

Investigators caution that more research is needed to explore connection between TV viewing and mortality and whether these same associations are found when we consider sitting in other contexts, such as driving, working, or doing other sedentary leisure-time activities. "Older adults watch the most TV of any demographic group in the U.S.," concluded Dr. Keadle. "Given the increasing age of the population, the high prevalence of TV viewing in leisure time, and the broad range of mortality outcomes for which risk appears to be increased, prolonged TV viewing may be a more important target for public health intervention than previously recognized." 

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Primary Reference:

Keadle, S. K., Moore, S. C., Sampson, J. N., Xiao, Q., Albanes, D., & Matthews, C. E. (2015). Causes of Death Associated With Prolonged TV Viewing: NIH-AARP Diet and Health Study. American journal of preventive medicine.