Colorectal cancer: risk factors

The main risk factors for colorectal cancer are as follows (SIGN 126):

Diet

The consumption of foods containing dietary fibre and relatively unprocessed cereals may help to decrease the risk of colorectal cancer. Likewise, the consumption of fruit and non-starchy vegetables may also decrease the risk, although the evidence is limited and merely suggestive.

Lack of physical activity

Physical activity is a factor that is convincingly associated with a decreased risk of colorectal cancer. UK guidelines on physical activity advise that adults should aim to have at least 150 minutes (2½ hours) of moderate exercise a week, either in bouts of 10 minutes or more or for 30 minutes on at least five days a week. Sedentary habits should be kept to a minimum.

Obesity

Both body fatness and abdominal fatness are categorised as convincing factors for developing colorectal cancer.

Long-term smoking

Recent studies suggest that long term smokers are found to be at elevated risk, with relative risks typically in the range of 1.5 to 3.0. The population of Scotland should be encouraged not to smoke, citing decreased colorectal cancer risk as one of the reasons.

Alcohol consumption

Alcohol consumption is a convincing risk factor for colorectal cancer in men and a probable risk factor in women. Consumption should be limited to no more than two drinks per day (30 g of ethanol or four units) for men and one drink per day (15 g of ethanol, two units) for women.

Other risk factors:

• A history of inflammatory bowel disease
• Genetic factors, such as familial adenomatous polyposis (FAP), and hereditary non-polyposis colorectal cancer (HNPCC)