The habit of sitting for long stretches at a time may raise the risk of developing cancer and dying from it, according to a new study. In contrast, sitting for the same amount of time but standing up periodically to move around or engage in light activity was found to help lower cancer risk.
A joint research team from the University of Glasgow in the United Kingdom and Harvard University's T.H. Chan School of Public Health in the United States announced that it had published its findings in the international journal PLOS Medicine. The study tracked 91,292 UK Biobank participants with no history of cancer over an average of 12.38 years.
The researchers had participants wear wrist-worn activity monitors (accelerometers) for seven days to analyze their movement. They then divided sitting time into "prolonged sedentary behavior," defined as sitting continuously for 30 minutes or more, and "intermittent sedentary behavior," which is frequently interrupted by movement, and analyzed the associations with cancer incidence and death.
One More Hour of Sitting Raises Cancer Death Risk 9%
The analysis found that for each additional hour per day spent sitting for long periods without a break, the overall risk of dying from cancer rose 9%. The overall risk of developing cancer also increased 3%.
The risk of developing obesity-related cancers—including esophageal, liver, kidney, pancreatic, colorectal, breast, ovarian, and thyroid cancers—rose 5%, and the risk of cancers associated with type 2 diabetes also increased.
Conversely, people who moved around periodically even while sitting for long hours had lower cancer risk overall.
Each additional hour per day of intermittent sedentary behavior was associated with an 18% lower overall risk of cancer death and a 6% lower overall risk of cancer incidence. The risk of developing obesity-related cancers and type 2 diabetes-related cancers fell 9% and 10%, respectively.
The research team concluded that how sitting time accumulates may matter more for health than prolonged sedentary behavior itself.
Washing Dishes and Walking Help Too: One Hour a Day Cuts Death Risk 12%
The researchers also analyzed the effect of replacing long periods of sitting with other activities.
Replacing one hour a day of prolonged sedentary behavior with light physical activity lowered the risk of cancer death by 12%. Light activity included household chores such as washing dishes and ironing, as well as walking.
About 30 minutes a day of moderate-intensity exercise reduced the risk of cancer death by 8%. Brisk walking is a representative example.
The greatest effect came from vigorous exercise. Just five minutes a day of high-intensity exercise, such as running or tennis, was found to lower the risk of cancer death by 22%.
The researchers explained that these results show it is important not only to increase exercise time but also to adopt lifestyle habits that frequently break up long periods of sitting.
"Health guidelines have so far focused on moderate- to high-intensity exercise, but this study shows that light movement should never be overlooked," the researchers said. "The finding that moving around frequently, even briefly, helps improve metabolic function more than sitting for long periods is also consistent with previous experimental research."
"Not Proof of Cause": Limitations of an Observational Study
However, the researchers stressed that because this was an observational study, it cannot be concluded that prolonged sitting directly causes cancer.
They also explained that participants' activity levels were measured for only seven days, and that UK Biobank participants tend to be more health-conscious and more physically active than the general population, limiting how directly the results can be applied to everyone.
In addition, they cited as a limitation of the study that the specific circumstances in which sedentary behavior occurred—such as whether participants were sitting for long hours at work or while driving—were not included in the analysis.
