5.3 Risk factors

Table 5.2 Risk factors for colorectal cancer, by direction of association and strength of evidence

Increases risk

Decreases risk

Convincing or probable

Family history of colorectal cancer1,2

Physical activity5,6,13


Tobacco smoking3,4

Hormone replacement therapy14



Oral contraceptives14,15


Greater body fatness, in particular, abdominal fatness5,6

Aspirin and other non-steroidal anti-inflammatory drugs16


Red and processed meat6

Foods containing dietary fibre6





Ionizing radiation3,8


Disinfection by-products in drinking water9

Non starchy vegetables6,17

Helicobacter pylori infection10


Insulin-like growth factor-1 (IGF-1)11





Vitamin B620,21


Milk, dairy and/or calcium24

Vitamin D25,26


1 First degree relative(s) with colorectal cancer; 2 Johns and Houlston, 2001; 3 colon cancer only; 4 Secretan et al., 2009;

5 International Agency for Research on Cancer, 2002; 6 World Cancer Research Fund / American Institute for Cancer Research, 2007; 7 Straif et al., 2009; 8 El Ghissassi et al., 2009; 9 Rahman et al., 2010; 10 Zhao et al., 2008; 11 Rinaldi et al., 2010; 12 Larsson et al., 2005; 13 Harriss et al., 2009; 14 International Agency for Research on Cancer, 2011a; 15 Bosetti et al., 2009; 16 International Agency for Research on Cancer, 1997; 17 International Agency for Research on Cancer, 2003; 18 Kennedy et al., 2011; 19 Galeone et al., 2010; 20 intake and blood levels; 21 Larsson et al., 2010; 22 in women only; 23 Yan et al., 2010; 24 Huncharek et al., 2009; 25 blood levels; 26 Yin et al., 2009

Up to 10% of colorectal cancers are hereditary and most are due to the genetic syndromes of familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC) (Hawkins and Ward, 2001). Excluding these syndromes, individuals who have a first degree relative with colorectal cancer have around a two-fold increased risk of developing the disease themselves.

Lifestyle factors are extremely important in colorectal cancer (Table 5.2). Smoking is causally related to colon, but not rectal, cancer. Alcohol is a cause of both colon and rectal cancers. Higher levels of body fatness, and in particular central adiposity, are positively related to risk. In a recent meta-analysis, each 5kg/m2 increment in body mass index was associated with an 18% increase in risk; the association appears stronger for colon than rectal cancer, for men than women, and in studies adjusting for physical activity (Ning et al., 2010). In contrast, physical activity is consistently inversely associated with colon cancer, in particular, and risk decreases in a dose-response fashion with increased frequency or intensity of activity. Regular use of aspirin or other non-steroidal anti-inflammatory drugs may reduce colorectal cancer risk by up to half. In addition, risk is decreased in women taking hormone replacement therapy and is likely also to be lower in those who have taken oral contraceptives.

Many studies have found increased risk in individuals who have higher intakes of processed meats (preserved by smoking, curing or salting, such as ham, bacon or salami) and red meats. In contrast, higher intake of various other dietary components may be associated with lower risk, including garlic; fruit; fish; non-starchy vegetables; milk, dairy products or calcium; coffee; soya and soya foods; and foods containing dietary fibre or the B vitamin folate.

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