Prolonged Sitting Linked To Higher Cancer Risk; Light Activity May Lower Mortality, Study Finds

Prolonged sitting has long been recognised as a risk factor for conditions such as diabetes, hypertension and cardiovascular disease. Now, a large international study suggests it may also increase the risk of developing and dying from cancer.

The encouraging finding, however, is that even light physical activity can help offset some of the harmful effects of prolonged sedentary behaviour.

The study, published in PLOS Medicine, found that every additional hour spent sitting continuously for at least 30 minutes was associated with a 9% higher risk of cancer-related death. Conversely, replacing just one hour of prolonged sitting each day with light physical activity was linked to a 12% lower risk of cancer mortality.

Researchers from the University of Glasgow and collaborating institutions analysed data from 91,292 participants enrolled in the UK Biobank. Participants wore wrist-based activity monitors continuously for seven days, enabling researchers to objectively measure patterns of movement and sedentary behaviour. They were then followed for a median period of 12.4 years to assess cancer incidence and mortality.

Unlike previous research, which largely focused on the total amount of time people spend sitting, the new study examined whether the pattern of sedentary behaviour—continuous sitting versus sitting interrupted by movement—makes a difference.

The findings suggest that how people accumulate sedentary time may be as important as how much time they spend sitting overall.

Researchers classified sedentary behaviour into two categories. Prolonged sedentary behaviour referred to uninterrupted sitting or reclining for at least 30 minutes during which at least 90% of the time was spent inactive. Interrupted sedentary behaviour consisted of shorter sitting periods or longer periods broken up by movement.

The analysis found that prolonged sedentary behaviour was associated not only with a higher risk of cancer mortality, but also with a greater likelihood of developing cancer overall. The strongest associations were seen for obesity-related cancers, including cancers of the oesophagus, liver, kidney, pancreas, colorectum, breast, ovary and thyroid, as well as cancers linked to Type 2 diabetes.

By contrast, individuals whose sitting time was regularly interrupted with brief periods of movement consistently showed a lower risk of cancer incidence and cancer-related death across all major outcomes examined.

The researchers said the findings reinforce growing evidence that breaking up prolonged periods of sitting may provide important metabolic benefits, even without engaging in vigorous exercise.

"Our findings suggest that the health effects of sedentary behaviour may depend not only on the total time spent sitting but also on whether that time is accumulated in prolonged bouts or interrupted by activity," the authors said.

They noted that experimental studies have previously shown that interrupting prolonged sitting with short periods of movement improves blood sugar regulation, insulin sensitivity and other metabolic responses compared with sitting continuously.

The study also raises questions about current public health recommendations, which primarily emphasise moderate- to vigorous-intensity exercise while paying relatively less attention to prolonged sitting.

The researchers said light activities such as standing, slow walking or moving around the house or workplace should not be overlooked as part of strategies to reduce cancer risk.

"Current health guidelines focus heavily on moderate or vigorous exercise, but our findings show that light movement should not be ignored," the authors said, adding that future clinical trials could help develop more personalised recommendations for reducing prolonged sedentary behaviour.

The study's strengths include its large sample size, objective measurement of physical activity using wearable devices rather than self-reported questionnaires, and long-term follow-up.

However, the researchers cautioned that the findings do not establish a cause-and-effect relationship. The study was observational and involved UK Biobank volunteers, who are generally healthier and more physically active than the wider population. As a result, the findings may not be directly applicable to all populations.

The researchers also acknowledged that they lacked information on the context of sedentary behaviour, such as whether participants were sitting while working, driving or engaging in leisure activities, factors that may influence health outcomes differently.

Nevertheless, the findings add to growing evidence that reducing prolonged sitting may become an important component of cancer prevention strategies alongside maintaining a healthy diet, avoiding tobacco, limiting alcohol consumption and engaging in regular physical activity.