In a new study that challenges the current thinking on colorectal cancer, researchers at the Occupational Cancer Research Centre of Cancer Care Ontario in Toronto have found that men and women involved in sedentary work are not at a greater risk of colon cancer than those who have jobs involving standing and walking.
The comprehensive study looked at data on occupations from 2.7 million people who filled out the 1991 Canadian long-form census and linked the results with records from the Canadian Cancer Registry between the years 1991 and 2011. Individuals were assigned a sedentary work category depending on how much sitting versus other body positions made up their daily work routines.
The researchers found a “weakly significant” reduced risk of colon cancer for those in jobs that involved a combination of sitting, walking, standing, crouching and bending. But perhaps surprisingly, no association was found between sitting-type jobs and either colon cancer or rectal cancer.
“The results from this analysis are novel because they provide detailed information on colorectal cancer risk by anatomical sub-site and sex in a national population representative of workers in hundreds of different jobs,” say the study’s authors, who found that their analysis “generally did not detect significant associations between sedentary work and colorectal cancer risk.”
The findings seem to go against conclusions from previous studies which have linked prolonged sitting with higher risks for a variety of cancers such as breast cancer and, particularly, colon cancer.
A 2014 study from the University of Regensburg in Germany found that women who spent a total of ten hours per day either sitting at work or watching TV had an eight per cent greater risk of colon cancer and a 10 per cent increased risk of endometrial cancer. Importantly, the study found the results to be the same regardless of how active a person was outside of those ten hours of sitting.
“The results were independent of physical activity, showing that sedentary behavior represents a potential cancer risk factor, distinct from physical inactivity,” said study author Dr. Daniela Schmid of the University of Regensburg, to Live Science.
The authors of the new study say that their results should be “interpreted cautiously,” as no further information about potential contributing factors (such as family history of colorectal cancer, diet and leisure time activity) was incorporated into the study.
Colorectal cancer is the second-most common cancer in Canada and the second-leading cause of death from cancer in men and third-leading cause for women. The Canadian Cancer Society estimates that 26,800 Canadians will be diagnosed with colorectal cancer in 2017, which represents 13 per cent of all new cancers cases.
There is a range of known risk factors for colorectal cancer, including not only having a sedentary lifestyle but also having a family history of the disease, being overweight or obese, eating a diet high in red meat, as well as alcohol and smoking.
A 2015 report by the World Health Organization made headlines with evidence that processed meats were linked to colorectal cancer, stating that more than 34,000 cancer deaths each year can be attributed to diets high in processed meats. By comparison, cancer caused by smoking causes about one million deaths annually, alcohol consumption causes 600,000 and air pollution 200,000.