Study suggests even light activity such as ironing could reduce health risks linked to prolonged sedentary behaviour Sitting for longer than half an hour at a time each day raises the risk of dying from cancer, a study suggests. Researchers who tracked more than 90,000 people over a decade found that sitting or lying down while awake for more than 30 minutes in one period each day was associated with an increased risk of cancer death. The risk increases for every additional hour of continuous inactivity, the findings suggest.