Colorectal Cancer

Ideas about causes of bowel (colorectal) cancer

The causes of bowel (colorectal) cancer in most people are still unknown but,

“The biggest single risk factor is age. 95 in 100 bowel cancers (95%) are diagnosed in people aged 50 or over. So the risk increases as you get older.’ Cancer Research UK January 2016 

Some families have a strong history of the disease and there are a number of inherited conditions such as FAP (familial adenomatous polyposis) and HNPCC (hereditary non polyposis colorectal cancer) which increase the risk of developing the disease. There is also evidence to suggest that it may be related to the diet of those who eat a lot of red and processed meat. Other risk factors include; a personal history of polyps, ulcerative colitis and Crohn’s disease (other chronic bowel diseases causing inflammation of the bowel), smoking, alcohol, being overweight and a lack of exercise. None of these risk factors necessarily mean you will develop the disease and some people who do develop it do not have any risk factors at all.

People interviewed in this study were often aware of the some of the risk factors currently supported by medical evidence but many could not link these to themselves. In these cases people often had their own ideas about why they had developed the disease. These ideas are summarised below and represent individual beliefs not proven facts. Nonetheless, people's own ideas about the possible causes of bowel (colorectal) cancer are important because they help us understand popular assumptions about who gets cancer and what kinds of behaviour might be linked to getting the disease. They also suggest possible avenues for future research.

Poor diet, heredity and stress were the factors most people named as likely causes of bowel cancer. Some people felt that they had become vulnerable to the disease because of their lifestyle or a combination of factors which, when added together, had triggered their illness. Others mentioned poor bowel habits and other bowel conditions as an issue while two people named environmental contamination as a possible cause of their disease. 

Most people were aware of a link between a diet high in red meat and processed meat and bowel (colorectal) cancer. One man recalled his liking for red meat, which he saw as the direct cause of his illness. But while many people shared this view of diet as a likely cause of the disease they felt that it did not apply in their case since their eating habits were fundamentally healthy. One man expressed anger at having developed cancer despite having always eaten well. Another woman strongly rejected the assumption that people who got bowel (colorectal) cancer necessarily had poor diets.

Heredity was seen as a likely cause by people who had colorectal cancer in the family. For some who were the first to have it, the link had been confirmed since pre-cancerous polyps had been found in family members who are now regularly checked for early signs of the disease. Others cited cancer in the family as a possible cause even if it was another kind of cancer or had affected distant relatives. One woman was undergoing investigation for a rare genetic syndrome associated with bowel (colorectal) cancer.

High levels of stress were identified by a number of people as the possible trigger of their illness whether the stress was related to work, relationships, or emotional trauma.

A lifestyle involving poor diet, lack of exercise, smoking and excessive drinking was generally felt to be one that could lead to a serious illness like bowel (colorectal) cancer. However many people could not understand why they had developed the disease since they had never lived in that way. People who thought their lifestyle might have contributed to their developing colorectal cancer often felt it was some combination of factors like overwork, diet, environment, and heredity. One woman who had always put other people's needs before her own felt that this could have contributed to her illness.

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Poor or irregular bowel habits were linked to the development of cancer by some people. One woman felt that delaying bowel movements and straining had caused an injury which later became cancerous. Another related her cancer to a history of constipation since childhood as well as another bowel disease (ulcerative colitis) in the family. 

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Environmental contamination was considered by two people to be a possible cause of their disease although they acknowledged that no link had so far been proven. One man had been exposed to radiation while in the RAF while another, whose wife has also had cancer, lives beside National Grid electricity wires.

Last reviewed August 2016.

Last updated August 2016.

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