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Sitting for hours on end could heighten someone’s risk of later dying from cancer, according to a sobering new study of the relationship between inactivity and cancer mortality. The study was epidemiological, providing a snapshot of people’s lives, so it cannot prove cause and effect. But the findings suggest that extremely sedentary people can be as much as 80% more likely to die of cancer than those who sit the least.

Still, the study also indicates that getting up and strolling for even a few additional minutes a day may lower the risk of dying from cancer.

There is plenty of evidence that spending all day in a chair is not healthy. But most of those studies relied on people’s undependable recollections. The studies also rarely examined whether and how occasional spurts of exercise might alter the risk equation.

For the new study, which was published in JAMA Oncology, researchers at the University of Texas MD Anderson Cancer Center and other institutions re-examined data collected as part of a large, nationwide study of risk factors for strokes.

That study had enrolled a multiracial group of more than 30,000 middle-age and older men and women and, starting in 2002, gathered details about their health, lifestyle and medical conditions.

Now, the researchers gathered the records for about 8,000 of the volunteers who had worn a tracker.

The men and women in the group that had spent the most hours sitting were 82% more likely to have died from cancer during the study’s follow-up period than those in the group that had sat the least. This association held true when the researchers controlled for people’s ages, weight, gender, health, smoking status, education, geographic location and other factors.

But the scientists also found that statistical models showed that for every 30 minutes of exercise instead of sitting, the risk of later dying from cancer fell by 31%. Even if someone substituted at least 10 minutes of usual sitting time with light-intensity activities, the risk of dying from cancer fell by about 8%.

“Even a small amount of extra physical activity, no matter how light it might be, can have benefits for cancer survival,” Dr. Susan Gilchrist said.