Spending your days in front of the television may contribute to a shortened lifespan, a new study suggests.
Researchers in Australia found that people who averaged six hours a day of TV lived, on average, nearly five years less than people who watched no TV.
For every hour of television watched after age 25, lifespan fell by 22 minutes, according to the research led by Dr. J. Lennert Veerman of the University of Queensland.
But other experts cautioned that the study did not show that TV watching caused people to die sooner, only that there was an association between watching lots of TV and a shorter lifespan.
Though a direct link between watching TV and a shortened lifespan is highly provocative, the harms of TV are almost certainly indirect, said Dr. David L. Katz, director of the Prevention Research Center at Yale University School of Medicine.
"As a rule, the more time we spend watching TV, the more time we spend eating mindlessly in front of the TV, and the less time we spend being physically active," Katz said. "More eating and less physical activity, in turn, mean greater risk for obesity, and the chronic diseases it tends to anticipate, notably diabetes, heart disease and cancer."
Another explanation for the possible link may be that people who watch excessive amounts of TV "are lonely, or isolated, or depressed, and these conditions, in turn, may be the real causes of premature mortality," he added.
The report was published in the Aug 15 online edition of the British Journal of Sports Medicine.
In the study, researchers used data on 11,000 people aged 25 and older from the Australian Diabetes, Obesity and Lifestyle Study, which included survey information about how much TV people watched in a week. Researchers also used national population and mortality figures.
In 2008, Australian adults watched a total of 9.8 billion hours of TV. People who watched more than six hours of TV were in the top 1 percent for TV viewing.
The statistics suggest that too much TV may be as dangerous as smoking and lack of exercise in reducing life expectancy, the researchers said.
For example, smoking can shorten of life expectancy by more than four years after the age of 50. That represents 11 minutes of life lost for every cigarette and that's the same as half an hour of TV watching, the researchers said.
Without TV, researchers estimated life expectancy for men would be 1.8 years longer and for women, 1.5 years longer.
"While we used Australian data, the effects in other industrialized and developing countries are likely to be comparable, given the typically large amounts of time spent watching TV and similarities in disease patterns," the researchers noted.
Dr. Gregg Fonarow, associate chief of cardiology at the David Geffen School of Medicine at University of California, Los Angeles, said that "there is increasing evidence that the amount of time spent in sedentary activity such at TV watching, distinct from the amount of time spent in purposeful exercise, may adversely impact health."
And although participating in a regular exercise program can help, it may not be enough to offset the risks of spending too much of the rest of the day — while at work or at home — getting no exercise whatsoever.
"Staying active and reducing time spent sedentary may be of benefit in reducing the risk of cardiovascular disease and may be considered as part of a comprehensive approach to improve cardiovascular health," Fonarow added.
Dr. Robert J. Myerburg, a professor of medicine at the University of Miami Miller School of Medicine, added that "a sedentary lifestyle can reduce life expectancy."
Myerburg isn't sure why sitting around is not good for your health. "It's better to look at it from a positive prospective," he said. "That is: a physically active lifestyle is protective."