Sedentary behaviour increases the risk of developing certain types of cancer, according to a new study by the University of Regensburg in Germany. Physical inactivity has been previously linked to diabetes, obesity and cardiovascular disease.

Researchers said that for every two hours spent sitting in front of the computer or television, the average person increases his or her risk of colon cancer by eight percent, endometrial cancer by 10 percent and of lung cancer by six percent. This statistic is irrespective of the amount of physical activity undertaken when not sitting.

This indicates that physically active people can heighten their risk of developing cancer by sitting down for too long.

For the study, the researchers analyzed data from 43 studies with more than four million participants and almost 70,000 cancer cases. All the studies involved questions relating to time spent watching TV and sitting at home or office.

The researchers found that lower levels of sedentary behaviour (associated with sitting) significantly increases risk for three cancers - bowel, endometrial (womb lining) and lung.

The researchers said that there are several biological reasons that describe the link between sedentary behaviour and cancer. TV viewing time was strongly associated with bowel and endometrial cancers - because it is often associated with the consumption of junk food and sugary beverages.

"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," stated 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."

Previous studies showed that people who watch six hours of TV per day shorten their lifespan by five years compared to those who don't. People associated with sedentary lifestyle have huge waistline, higher levels of cholesterol, blood sugar and triglycerides.

Graham Colditz, an expert at Washington University School of Medicine, said that current life demands less physical activity and 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," Colditz said.

The finding is published in the Journal of the National Cancer Institute.