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Just as more people are spending their lockdown hours sitting around at home comes news that you won’t want to hear: inactivity is associated with greater risk of cancer.

But there is good news: 30 minutes on your bike is all it takes to lower the risk by 31%.

The findings have emerged from an important study at the Texas University Anderson Cancer Centre—the first to look at objective measures of sedentary behaviour and cancer mortality.

The most sedentary individuals had an 82% higher risk of cancer mortality compared to the least sedentary individuals.

Rather than relying on participants to self-report their activity levels, an accelerometer was used to measure physical activity.

"This is the first study that definitively shows a strong association between not moving and cancer death," said Susan Gilchrist, M.D., associate professor of Clinical Cancer Prevention and lead author of the study, published in JAMA Oncology.

"Our findings show that the amount of time a person spends sitting prior to a cancer diagnosis is predictive of time to cancer death."

Researchers also found that replacing 30 minutes of sedentary time with physical activity was associated with a 31% lower risk of cancer death for moderate-intensity activity, such as cycling, and an 8% lower risk of cancer death for light-intensity activity, such as walking.

"Conversations with my patients always begin with why they don't have time to exercise," said Gilchrist, who leads MD Anderson's Healthy Heart Program.

"I tell them to consider standing up for 5 minutes every hour at work or taking the stairs instead of the elevator. It might not sound like a lot, but this study tells us even light activity has cancer survival benefits.”

Sedentary behaviour is associated with several health outcomes, including diabetes, cardiovascular disease, and all-cause mortality.

Less is known about the association between objectively measured sedentary behaviour and cancer mortality, as well as the association with physical activity.

This study involved a cohort of participants from the nationally representative REGARDS (REasons for Geographic and Racial Differences in Stroke) study, which recruited more than 30,000 U.S. adults over the age of 45 between 2003 and 2007 to study long-term health outcomes.

To measure sedentary behaviour, 8,002 REGARDS participants who did not have a cancer diagnosis at study enrolment wore an accelerometer on their hip during waking hours for seven consecutive days.

The accelerometer data was gathered between 2009 and 2013. After a mean follow-up of 5 years, 268 participants died of cancer.

Longer duration of sedentary behaviour was independently associated with a greater risk of cancer death.

The study also found that engaging in either light or moderate to vigorous physical activity made a difference.

Investigators assessed sedentary time, light-intensity physical activity (LIPA) and moderate to vigorous physical activity (MVPA) in the same model and found that LIPA and MVPA, not sedentary behaviour, remained significantly associated with cancer mortality.

"Our findings reinforce that it's important to 'sit less and move more' and that incorporating 30 minutes of movement into your daily life can help reduce your risk of death from cancer," Gilchrist said.