- Researchers in the United Kingdom took a closer look at sedentary behavior, cancer risk, and cancer-related death.
- They found that each additional hour per day of prolonged, uninterrupted sitting was associated with about a 9% higher risk of cancer-related death.
- Each additional hour of sedentary time that was broken up by movement, however, was associated with a lower risk of cancer death.
Sedentary behavior is linked to health risks, and guidance typically focuses on total sedentary time rather than on whether that time is broken up with physical activity.
A new study found that the pattern of sedentary behavior may be just as important as the total amount of sitting time, especially concerning cancer.
The researchers observed an association between replacing prolonged sitting with physical activity and a lower risk of cancer. Depending on the activity’s intensity, the reduction in cancer mortality risk ranged from 8% to 22%.
The study is published in PLOS Medicine.
Extended vs. interrupted sitting
Sedentary behavior is defined as being awake and sitting, reclining, or lying down with “low energy expenditure.”
According to the US Department of Health and Human Services’
The guidelines note that replacing sedentary time with light-intensity movement, such as walking, can provide health benefits. Moderate-to-vigorous activity, such as playing tennis or running, may offer more protection.
The researchers in the new study wanted to determine whether the pattern of sedentary behavior, rather than just the total amount, was associated with cancer risk, and whether replacing prolonged sitting with physical activity might influence that risk.
The study used data from more than 91,000 adults in the UK Biobank, a large population-based cohort. Participants wore wrist accelerometers for 7 days to measure physical activity and sedentary behavior.
The researchers divided sedentary behavior into two main categories:
- prolonged sedentary behavior (sitting for at least 30 minutes without interruption)
- interrupted sedentary behavior (sitting time broken up by movement)
The scientists used around 12 years of records to track cancer diagnoses during follow-up.
How prolonged sitting increases health risks
After gathering the data, the researchers used statistical models to determine whether there was a relationship between sedentary behavior and cancer outcomes. They also used substitution models to estimate how replacing sitting time with other activities might affect those risks
Prolonged sedentary behavior showed higher overall cancer incidence, higher cancer mortality, and a greater risk of obesity-related and type 2 diabetes-related cancers.
Frequent interruptions of sedentary time with movement (such as household chores, walking, or vigorous exercise) were associated with lower cancer risk across multiple cancer types.
The researchers found a similar pattern when they examined cancer-related deaths.
Each additional hour of prolonged sitting carried about a 9% to 10% higher risk of cancer death. However, each additional hour of sedentary behavior interrupted corresponded to a lower risk of cancer death.
The benefits depend on the movement type and amount.
Replacing 1 hour of prolonged sitting with light physical activity was associated with a 12% reduction in cancer-related death risk. Replacing 30 minutes of moderate activity with vigorous activity was linked to an 8% reduced risk, and replacing just 5 minutes of prolonged sitting with vigorous activity was associated with a 22% lower risk.
Overall, the findings suggest that breaking up long periods of sitting with movement may be an important strategy for reducing cancer risk. Since this study is observational, more research is necessary to confirm the findings.
Why breaking up sitting time is important
David Yashar, MD, a hematologist/oncologist at MemorialCare Todd Cancer Institute at Long Beach Medical Center, shared his thoughts on the study with Medical News Today. I have explained why sedentary behaviors may lead to cancer.
“A sedentary lifestyle can lead to a person becoming overweight/obese,” Yashar explained. “We know that an increased amount of fat causes inflammation, which is a known risk factor for cancer.”
Yashar also noted that a sedentary lifestyle can contribute to hormonal imbalances, which “can lead to increased risk of hormone-sensitive cancers such as breast cancer.”
He said breaking up prolonged sitting with movement can “increase antioxidant defenses, which can therefore reduce reactive oxygen species.” This is important because it reactive oxygen species
Yashar encouraged people to take a break from prolonged sitting by getting up every 15 minutes to “grab some water or walk around for a couple of minutes.”
Hector Perez, MD, a board certified bariatric surgeon at Renew Bariatrics and an advisor at Bariatric Journalalso spoke with MNT. While acknowledging that the findings indicating that prolonged sitting is unhealthy were not surprising, Perez said the fact that how people sit is more important than their cumulative sitting time was interesting.
“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,” explained Perez.
Perez cautioned people against interpreting the reported 9% higher risk of cancer death for each additional hour of prolonged sitting as an absolute risk. He reminded that the study found an association, not a direct cause.
Instead, Perez encouraged readers to focus on the study’s more practical findings, noting that replacing even a few minutes of prolonged sitting with physical activity could help reduce health risks. He said the study already reinforces an important clinical message: meeting daily exercise goals doesn’t necessarily offset the effects of spending the rest of the day sitting still.
“That box-checking mentality is exactly what this paper challenges,” Perez said.
