People diagnosed with colorectal cancer who spend a lot of their leisure time sitting have a higher risk of dying, according to researchers at the American Cancer Society.
People who are physically active, however, have a better chance of surviving than those who aren't, the researchers said.
"One factor might be that people who are physically active might be developing a less aggressive tumor," said lead researcher Peter Campbell, director of the society's Tumor Repository.
In addition, being physically fit may help people as they undergo treatment, he said.
Exercise improves cardiovascular and muscle fitness, lowers blood pressure and cholesterol, and improves blood sugar, Campbell noted. "Some of these factors would lead quite clearly to better tolerance for getting through surgery or other treatments," he said.
Campbell said the connection between sitting and dying isn't well understood.
"The sitting time is a little more speculative," Campbell said. "We do understand that sitting for long periods can lead to worse insulin and glucose profiles [measurements]. These worse insulin and glucose [measurements] can feed a tumor and increase risk of recurrence and death."
There is also evidence that long periods of sitting increases "oxidative stress" on the body's cells and worsens hormone balances, he added.
The new results need to be replicated before they can be considered definitive, but they are consistent with what is seen in non-cancer patients, Campbell said. Although the study suggests an association between exercise and better outcomes, it did not prove cause and effect. Many studies, however, have found this association not only for cancer, but for heart disease and other conditions.
Moreover, the benefits of exercise in maintaining normal body weight and improving strength and endurance are indisputable and add to overall health, Campbell said.
The report was published Jan. 22 in the Journal of Clinical Oncology.
For the study, Campbell's team collected data on nearly 2,300 people diagnosed with colorectal cancer that had not spread beyond the colon. During 16 years of follow-up, more than 800 patients died, nearly 400 of them from colorectal cancer and the rest from other causes.
After examining the data, Campbell's group found that people who exercised the most — such as walking 150 minutes a week — had about a 28 percent lower risk of dying compared to those who exercised less.
Sitting six hours or more a day during leisure time was linked to a 36 percent increased risk of dying compared to sitting less than three hours a day, the study found.
"I think this applies to more than colon cancer, because what they are describing is all-cause mortality not just mortality from colon cancer," said Dr. David Bernstein, a gastroenterologist and chief of the division of hepatology at North Shore University Hospital in Manhasset, N.Y.
"They are reinforcing that exercise and physical activity is associated with a lower risk of dying and it's better for you than just sitting there doing nothing," he said. "The body was meant to move around."