Study details and key findings

For the study, researchers analyzed data from 91,292 participants who were part of the U.K. Biobank prospective cohort study. None of the participants had a history of cancer at baseline, and all of them reported a week of physical activity data from an accelerometer, which measured the intensity and duration of physical activity. The mean age of participants was 56 years old and 56% were women.

The researchers classified physical activity as low (walking at a slow speed), moderate (walking at a moderate speed), and vigorous (fast walking and high-energy activity). They also defined prolonged sedentary behavior as a period of at least 30 minutes when at least 90% of the time was sedentary.

Among the participants, 12,392 were diagnosed with cancer, and 1,726 died of cancer. According to the researchers, prolonged sedentary behavior was associated with higher overall cancer incidence, higher cancer mortality, and an increased risk of obesity-related and type 2 diabetes-related cancers. For each additional hour of prolonged sedentary behavior, participants had 9% to 10% higher risk of cancer mortality.

Commentary

According to Hector Perez, a board-certified bariatric surgeon at Renew Bariatrics and an advisor at Bariatric Journal, one of the study's key findings is that how people spend their sedentary time matters more than their cumulative sedentary time.

"The study indicates that your body responds to the shape of that sedentary time, so a single unbroken 90-minute stretch appears to do something different than the same 90 minutes chopped into six smaller interrupted sessions," Perez said.

The researchers also noted that the study's findings suggest that even light physical activity or movement can be beneficial to health.

"Current health guidelines focus heavily on moderate or vigorous exercise, but our findings show that light movement shouldn't be ignored," the researchers wrote. "Moving forward, clinical trials will help us move beyond blanket advice and develop personalized strategies for breaking up sitting time."

Similarly, David Yashar, a hematologist and oncologist at MemorialCare Todd Cancer Institute at Long Beach Medical Center, noted that breaking up prolonged sedentary behavior with movement can "increase antioxidant defenses, which can therefore reduce reactive oxygen species." Reactive oxygen species can lead to inflammation, which is a known risk factor for cancer.

To avoid being sedentary for too long, Yashar recommends people take a break from prolonged sitting every 15 minutes by getting up to "grab some water or walk around for a couple of minutes." Previous research has also suggested that even five minutes of physical activity every half hour could offset the health risks associated with hours of sitting.