London - Sit down less often if you want to avoid cancer, warn researchers.
The risk of developing some cancers rises by as much as 10 percent for every two hours more a person spends sitting than normal – whether or not they are physically active the rest of the time.
Scientists came to the conclusion after pooling the results of 43 studies with 4 million participants and almost 70 000 cancer cases.
The risk was based on a scale of participants’ hours of activity and inactivity and how this related to cancers developing.
Even among those who took regular exercise, every extra two hours – on a sliding statistical scale – spent sitting was associated with a 10 percent increased chance for women of developing cancer of the womb lining. The risk of bowel and lung cancers was raised by 8 percent and 6 percent respectively.
There is growing evidence that suggests too much sitting – as opposed to insufficient activity – may be a new risk factor for premature death and illnesses such as diabetes and heart disease.
All the studies involved lifestyle questionnaires on activities such as TV viewing time, sitting time at home and at work, and total sitting time.
Comparing the highest and lowest levels of sitting revealed a statistically significant increased risk for three cancers – bowel, endometrial (womb lining) and lung.
Study authors Daniela Schmid and Dr Michael Leitzmann, from the University of Regensburg in Germany, say there are several possible biological reasons for the link. TV viewing time was most strongly associated with bowel and endometrial cancers – possibly because it is often accompanied by eating junk food and drinking sugary beverages.
People who sit for longer have bigger waist sizes and higher levels of cholesterol, blood sugar and triglycerides – a type of fat that is found in the blood.
The average adult spends 90 percent of their leisure time sitting down.
Sitting “has a detrimental impact on cancer even among physically active persons”, the report, in the Journal of the National Cancer Institute, concluded.
This means that “limiting the time spent sedentary may play an important role in preventing cancer”, it added.
In the same journal, Graham Colditz, an expert at the Washington University School of Medicine, pointed out that modern technology means daily life now demands less physical activity and “more sitting”.