• This effect holds even for people who do a lot of exercise when not sitting
• The increased risk was most notable for womb, bowel and lung cancers

MailOnline
By JENNY HOPE MEDICAL CORRESPONDENT
PUBLISHED: 15:02 EST, 16 June 2014 | UPDATED: 12:42 EST, 17 June 2014

Stop sitting down if you want to avoid cancer, warn researchers.

The risk of developing some cancers rises by up to 10 per cent for every extra two hours sitting, according to a new review of studies.

Worryingly, say scientists, the effect appeared to be unrelated to how much exercise people took when not sitting.

This suggests that even people who are generally physically active may increase their cancer risk by sitting down for too long.

Scientists came to the conclusion after studying pooled data from 43 studies with more than four million participants and almost 70,000 cancer cases.

There is growing evidence which suggests too much sitting – as opposed to insufficient activity – may be a new risk factor for premature death and illness such as diabetes and heart disease.

All the studies in the review involved questionnaires and interviews probing lifestyle habits related to activity such as TV viewing time, sitting time at home and at work, and total sitting time.

Comparing the highest and lowest levels of sedentary behaviour revealed a statistically significant increased risk for three specific cancers – bowel, endometrial (womb lining) and lung – associated with sitting.

Every extra two hours spent sitting was associated with a 10 per cent increased chance for women of developing cancer of the womb lining.

The risk of bowel and lung cancers was raised by eight per cent and six per cent respectively.

Study authors Daniela Schmid and Dr Michael Leitzmann, from the University of Regensburg in Germany, in a report in the Journal of the National Cancer Institute, say there are several possible biological reasons for the link between sedentary behaviour and cancer.

TV viewing time was most strongly associated with bowel and endometrial cancers – possibly because watching TV is often accompanied by eating junk food and drinking sugary beverages, said the researchers.

‘Time spent sedentary displaces light intensity physical activity, causing decreased energy expenditure accompanied by weight gain and obesity, which are related to increased risk of cancer,’ says the report.

Previous research found people who watch six hours of TV a day cut short their lifespan by five years compared with someone who watches no TV.

People who sit for longer have bigger waist sizes, and higher levels of cholesterol, blood sugar and triglycerides.

The average adult spends 90 per cent of their leisure time sitting down and less than half of adults meet World Health Organisation physical activity recommendations.

In the UK, adults are urged to do 150 minutes of activity a week to promote health.

But guidelines in the UK and U.S. need to go further and promote moving about rather than sitting down, says the report.

‘That sedentariness has a detrimental impact on cancer even among physically active persons implies that limiting the time spent sedentary may play an important role in preventing cancer,’ it says.

Graham Colditz, an expert at Washington University School of Medicine, writing an editorial in the same journal, said daily life now demands less physical activity and ‘induces more sitting’ thanks to modern technology.

‘We accumulate sedentary time from sitting at school or work, motorised transport, watching TV, computer gaming, and so on,’ he said.

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