Evidence Emerges for the Health Risks of Sedentary Behavior

Division of Cancer Epidemiology and Genetics

At home, at work, and in the community, people today are moving less and sitting more than previous generations, and researchers are just beginning to understand the health risks associated with these behavior trends. Until recently, population-based research focused on the adverse effects associated with inadequate levels of exercise. But the latest evidence suggests that too much sitting – sedentary behavior – also has ill effects, and that these effects are distinct from those of too little exercise.

One researcher studying these issues is Charles Matthews, Ph.D., a physical activity epidemiologist in NCI’s Division of Cancer Epidemiology and Genetics. He and his colleagues used information from the NIH-AARP Diet and Health Study, which was developed at NCI, to examine the independent effects of sedentary behavior and exercise on the risk of death due to various causes, including cancer. The researchers found that prolonged television viewing and overall sitting time were associated with an increased risk of death (mortality) from all causes. Higher amounts of television viewing were also linked to an increased risk of death from cardiovascular disease and cancer. Compared with those who reported watching less than 1 hour of television per day, people who watched 7 or more hours per day had a 60% greater risk of dying from all causes, nearly twice the risk of death due to cardiovascular disease, and a 20% greater risk of death due to cancer.

“Our study was one of the larger studies, and one of only a handful, that has shown evidence of a link between sedentary behavior and cancer mortality,” Dr. Matthews noted. Other reports from the NIH-AARP study have demonstrated links between sedentary behavior and increased risks of colon and endometrial cancer in particular, he added.

“Probably the most striking thing we saw was that even among people who reported 4 to 7 hours a week of exercise, those who also reported 5 or 6 hours per day of television viewing still had an increased likelihood of death from all causes and from cardiovascular disease compared to individuals who reported less than an hour a day of television viewing,” Dr. Matthews said. In other words, “in terms of the risk for death, participating in a fair amount of exercise each week doesn’t completely inoculate you against the deleterious effects of spending a lot of time in front of the television set.”

The researchers followed more than 240,000 participants in the NIH-AARP Diet and Health Study, age 50–71 years old at the start of the study, for an average of 8.5 years. At the start of the study, the participants reported their average daily television or video viewing time, overall sitting time in the past year, and the average amount of leisure time per week spent in moderate to vigorous physical activity, or exercise, over the past 10 years. Examples of moderate to vigorous physical activity included walking for exercise, running or jogging, swimming laps, and heavier lawn and garden work.

Dr. Matthews explained that, in this study, prolonged time in front of the television was more strongly linked with increased mortality than overall sitting time because a single question that asks how long people spend sitting each day overall is probably not reported as accurately as a single question about a specific sitting behavior, in this case television viewing.

“Our results add to the growing evidence that the adverse effects of sedentary behavior seem to be independent of the benefits of exercise,” Dr. Matthews said. The finding, he noted, “opens the door for developing new strategies to increase the overall activity level of the population by reducing sedentary time in favor of more active pursuits. To date, our primary strategy has been to encourage exercise participation.”

“It’s really a wake-up call to think about all of the many different places you sit during daily life and [try to] switch to an upright and active approach to doing those same activities,” Dr. Matthews continued. For instance, he added, at home “you can stand up to fold laundry or cook meals. You can rearrange your computer workstation so you are able to stand [at the computer].” Taking frequent breaks to walk around the room, house, or office may also be helpful, he said.

The NCI researchers found that their results didn’t change much when they adjusted for Body Mass Index (BMI), which is a measure of obesity, suggesting that factors other than obesity account for the ill effects of sedentary behavior.

Dr. Matthews and his colleagues are now analyzing information from more detailed questionnaires that were administered as part of the NIH-AARP Diet and Health Study to find out how much and what types of activity can minimize the health risks associated with sedentary behavior, including activities such as household chores, lawn and garden work, caring for children and elders, and home repairs.