A new study has found that watching TV for at least three hours a day increases the risk of death from major illnesses like diabetes, liver disease and heart disease. The longer the hours people spend in front of the TV, the greater that risk becomes, according to researchers from the National Cancer Institute.

Previous studies have shown that watching TV is associated with an increased risk of death from cancer and cardiovascular disease, but how it is linked with other health risks is not known. To determine how watching TV is associated with the leading causes of death in the U.S., the researchers studied 221,000 individuals who did not have chronic disease. The study participants were aged 50 to 71 years old.

The results of the study confirmed that watching TV is linked with a higher risk of death from cancer and cardiovascular disease. Additionally, the study showed that watching TV increased the risk of death from other major illnesses like pneumonia, diabetes, liver disease, Parkinson's disease and chronic obstructive pulmonary disease. It also increased the risk of dying from suicide.

"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," lead study author Sarah K. Keadle from the Division of Cancer Epidemiology and Genetics at the National Cancer Institute said in a press release. "In this context, our results fit within a growing body of research indicating that too much sitting can have many different adverse health effects."  

The researchers reported that those who watched TV three to four hours daily had a 15 percent higher mortality risk, while those who watched seven hours or more had a 47 percent higher mortality risk compared to those who watched TV for less than an hour. Even as other factors were taken into consideration, such as smoking and alcohol intake, the link between watching TV for at least three to four hours a day and mortality risk remained the same.

Surprisingly, it did not matter if the participants exercised or not; the results applied to both active and inactive individuals. However, replacing TV viewing with exercise would have some health benefits.

"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," Keadle said.

The researchers said that more studies are needed to investigate the link between watching TV and mortality risk.

"Older adults watch the most TV of any demographic group in the U.S.," Keadle noted. "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."

The study is published in the December issue of American Journal of Preventive Medicine.