The findings of television's effects on physical activity are the first to be based on objective measurements using pedometers, rather than the study subjects' memories of their physical activity, say the researchers. The study will be published online by the American Journal of Public Health on July 27 and later in the journal's September 2006 issue.
"Clearly the more time a person spends watching television the less time they have to be physically active, and in many lower income communities, other factors might have influenced the study participants' decisions to spend time watching television," said the paper's lead author, Gary Bennett, PhD, of Dana-Farber's Center for Community-Based Research and the Harvard School of Public Health.
These factors may include fear of street crime and poor maintenance of parks and playground equipment, which create barriers to outdoor activities. Older people were particularly prone to staying indoors and watching television, which reflects their increasing isolation in society today, Bennett said.
The study involved 486 low-income housing residents in Boston. The study participants tended to be black or Hispanic, older, and female. Two-thirds were overweight or obese, 37 percent had less than a high-school education.
To avoid the potential inaccuracies associated with self-reported physical activity, the researchers arranged to have the study participants wear pedometers during their waking hours to count the number of steps they took every day for five days. The pedometers were "blinded" to prevent the participants from knowing how many steps they had taken and possibly altering their normal patterns of activity. The participants also reported the number of hours they watched television.
Results showed that the participants watched an average of 3.6 hours a day of television, with some reporting spending no time watching television while others watched as much as 14.5 hours on weekdays and 19 hours on weekend days.
Researchers have estimated that 10,000 steps a day measured with a pedometer roughly approximates recommended daily activity levels. In the current study, on an average day, each hour of television viewing was associated with 144 fewer steps walked – or an average of 520 fewer steps a day for those who spent 3.6 hours in front of the television.
In addition, for each hour of television they watched, participants were 16 percent less likely to achieve the 10,000-step-per-day goal. For those who watched the 3.6-hour-a-day mean value, their odds of walking 10,000 steps a day were 47 percent less than non-television-watchers.
The study findings represent "a piece of a larger puzzle for us – how do we help people to become more active?" said Bennett. Simply telling people not to watch television "doesn't work terribly well," he explained, and often leads to substituting other sedentary activities like reading and computer use.
Going forward, "we need to do a better job of understanding the factors that lead people to be physically active," Bennett said. "This is an important area of research, particularly because the impact of physical inactivity disproportionately affects the health of lower income Americans."
Contact: Janet Haley Dubow [email protected] 617-632-4090 Dana-Farber Cancer Institute