We have long known that sitting too much is bad for our health. Numerous studies have demonstrated the detrimental effects of prolonged sitting. However, recent research suggests that we should pay attention to more than just the total amount of time spent sitting each day.
A first-of-its-kind study published in the journal PLOS Medicine reveals that how we distribute and accumulate periods of prolonged sedentary behavior throughout the day can have a significant impact on health.
The researchers’ most striking finding was that for every additional hour of prolonged sitting during the day, participants faced a significantly higher risk of developing cancer and dying from it.
“Our data show that sitting for more than 30 minutes at a time is specifically linked to an increased risk of cancer,” says epidemiologist and lead author Frederick Ho from the University of Glasgow. “The good news is that breaking up sedentary time—for instance, with a short walk—can have a protective effect.”
For the study, scientists analyzed data from over 91,000 participants in the UK Biobank—a long-term research project tracking the health of approximately half a million people in the UK.
The study found that each additional hour of prolonged sitting was associated with a 9% increase in the risk of cancer death.
The average age of the participants in this group was 56, and none had a history of cancer.
Each participant wore a wrist-based activity monitor with an accelerometer continuously for seven days; the device tracked their movement levels, categorizing them as sedentary behavior or light, moderate, or vigorous physical activity. The researchers then monitored their health status for approximately 12 years.
During the follow-up period, the researchers found that overall sedentary behavior was linked to poorer health outcomes—including an increased risk of cancer diagnosis and cancer-related death—even after adjusting for age, sex, ethnicity, socioeconomic status, education level, and factors related to diet and lifestyle.
However, upon examining patterns of sedentary time, the researchers discovered that not all time spent sitting is created equal.
Specifically, they measured two distinct types of sedentary activity: prolonged sedentary behavior (sitting bouts lasting 30 minutes or longer, with 90 percent of that time spent seated) and intermittent sedentary behavior (sitting bouts lasting less than 30 minutes, or longer periods frequently interrupted by non-sedentary activity).
The data revealed a significant difference between these two types of sedentary behavior.
The results showed that for every additional hour per day spent sitting, the study participants faced a 9 percent higher risk of dying from any type of cancer.
Each additional hour spent sitting was also associated with a 3 percent increase in cancer incidence, with the incidence of obesity-related and type 2 diabetes-related cancers rising by 5 percent.
While these relative risk estimates might appear modest, the cumulative effect of time is crucial, as each hour adds to the risk of developing cancer.
In contrast, intermittent sitting was associated with significantly better health outcomes.
Each hour of intermittent sedentary behavior was linked to an 18 percent lower risk of cancer death and a 6 percent reduction in overall cancer incidence. Among those who periodically changed their location, the incidence of obesity-related cancers and type 2 diabetes-related cancers also decreased by 9% and 10%, respectively.
“Our results suggest that the health impact of a sedentary lifestyle may depend not only on the total time spent sitting but also on whether that time accumulates in long stretches or is interrupted by physical activity,” the researchers explain in their article. “This pattern is biologically plausible: experimental studies have shown that breaking up prolonged sitting with short bursts of activity can improve metabolic responses compared to continuous sitting.”
In addition to comparing two types of sedentary behavior, the study results also revealed new evidence regarding the importance of …physical exercises to counteract such health issues.
Modeling results indicate that replacing just one hour of sedentary behavior per day with physical activity can lead to noticeable health improvements associated with a reduced risk of developing cancer.
In the study, replacing one hour of prolonged sedentary behavior daily with light physical activity corresponded to a 12 percent reduction in cancer mortality risk and a 6 percent reduction in cancer incidence.
“Current health guidelines largely focus on moderate or vigorous physical exercise, but our research shows that light physical activity should not be overlooked either,” says Ho.
Of course, it should be noted that due to the nature of this observational study, the findings indicate associations within the data rather than proving that altering a sedentary lifestyle in this way will necessarily reduce an individual’s risk of developing cancer.
However, the results align with a range of related studies, including those demonstrating a link between sedentary behavior and chronic inflammation, as well as research showing how physical activity can aid in cancer prevention.
In this context, it is worth noting that even very small amounts of daily activity that break up long periods of sitting appear to be beneficial for our health, and we should not lose sight of this.
“To our knowledge, this is the first study to show a differential association between intermittent and prolonged sedentary behavior and cancer outcomes,” the researchers write. “Given the high prevalence of sedentary behavior, even modest associations could have significant public health implications.”
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