Sitting or lying down while awake for more than 30 minutes at a time is associated with a higher risk of dying from cancer, according to a study involving more than 91,000 people.
Researchers found that the risk increased as participants spent more time in long periods of inactivity. However, replacing some sedentary time with light, moderate, or vigorous movement was associated with a lower risk.
The researchers analysed information collected through wearable devices used by more than 91,000 UK Biobank participants.
They followed the participants for an average of 12 years and examined how the length of sedentary periods related to cancer deaths.
Each additional hour spent in prolonged inactivity every day was associated with a 10% higher risk of dying from cancer. Prolonged inactivity refers to sitting or lying down while awake for periods lasting more than 30 minutes.
Breaking up longer periods of sitting with physical activity was associated with a reduced risk.
Replacing one hour of sedentary time each day with light activity, including ironing, washing dishes, slow walking, or other household work, was linked to a 12% lower risk of cancer death.
Replacing 30 minutes of inactivity with moderate exercise, such as walking at an average pace, was associated with an 8% reduction.
The study also found a 22% lower risk when participants replaced five minutes of sedentary time with five minutes of vigorous activity each day.
Lead researcher Dr Frederick Ho of the University of Glasgow said the results showed that sitting for more than half an hour at a time was particularly associated with cancer risk.
He said even a simple activity, such as taking a short walk every 30 minutes, could help. The findings also suggest that health guidance should not focus only on moderate or vigorous exercise, as light movement may also be beneficial.
The findings were published in PLOS Medicine and came from an observational study.
This means the researchers identified an association between prolonged inactivity and cancer deaths but could not establish that sitting for long periods directly caused the increased risk.
Further research, including clinical trials, will be needed to confirm the results and determine the most effective ways to break up sedentary time.
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