Sitting for long, uninterrupted periods may be more harmful than simply spending a large amount of time sedentary, new research suggests.

A study of more than 91,000 adults found that each additional hour of prolonged sedentary behaviour per day was associated with a 9% higher risk of dying from cancer. However, replacing prolonged sitting with light physical activity was associated with a lower risk.

The findings, published in PLOS Medicine, suggest that how long people sit without moving may matter alongside how much time they spend sitting overall.

How Much Sitting Is Too Much?

There is currently no specific daily limit for sitting that health authorities consider 'safe'. The NHS advises adults to reduce the amount of time they spend sitting or lying down and to break up long periods of inactivity with some form of movement.

In the new study, researchers from the University of Glasgow and colleagues analysed activity-monitor data from 91,292 UK Biobank participants. The participants wore activity monitors for seven days and were followed for a median of 12.38 years.

The researchers classified prolonged sedentary behaviour as periods lasting at least 30 minutes during which at least 90% of the time was spent sedentary.

Each additional hour of prolonged sedentary behaviour was associated with a 9% higher risk of cancer death. Prolonged sitting was also associated with a higher risk of developing cancer overall and several obesity-related and type 2 diabetes-related cancers.

Importantly, these figures describe an association, not proof that sitting directly causes cancer. The research was observational, meaning other factors could partly explain the findings.

Does Getting Up Every 30 Minutes Help?

The findings suggest that interrupting sedentary periods may be beneficial.

Replacing one hour of prolonged sedentary behaviour each day with light physical activity was associated with a 12% lower risk of dying from cancer. Light activity could include walking slowly or doing household tasks such as washing dishes or ironing.

Replacing 30 minutes of prolonged sedentary behaviour with moderate physical activity was associated with an 8% lower risk of cancer death. This does not mean people need to complete a workout every time they stand up. Even brief periods of movement may be preferable to remaining completely inactive.

The NHS recommends that adults aim for at least 150 minutes of moderate-intensity physical activity each week, or 75 minutes of vigorous activity, alongside strength exercises on at least two days a week. It also recommends breaking up long periods of sitting.

What Can You Do if You Sit All Day?

People who work at a desk, drive for long periods, or spend several hours watching television may find it difficult to avoid sitting altogether. Instead, the practical goal is to interrupt prolonged periods of inactivity.

Try standing up and walking around regularly, taking short walking breaks during the working day, standing while making phone calls, or doing simple household tasks between periods of sitting. The researchers stressed that light movement should not be overlooked simply because it does not qualify as traditional exercise.

Ultimately, the study does not establish a precise number of hours that people can sit before cancer risk increases. But it does provide another reason to avoid spending hours sitting without a break. For people with sedentary routines, moving more frequently throughout the day may be a simple place to start.

Frequently Asked Questions

  • What is the risk associated with prolonged sitting?
    Prolonged sitting is associated with a higher risk of dying from cancer and developing several obesity-related and type 2 diabetes-related cancers.
  • How can I reduce the risk of cancer associated with sitting?
    Interrupt prolonged periods of sitting with light physical activity, such as walking slowly or doing household tasks, to lower the risk of cancer.
  • How often should I move to reduce cancer risk?
    It is beneficial to stand up and move every 30 minutes to break up prolonged periods of sitting.
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