Links between lifestyle and bowel cancer
Bowel cancer is increasingly linked to lifestyle; in recent decades, there has been considerable interest in identifying modifiable risk factors.
Research into preventable risk factors for bowel cancer has focused mainly on:
- diet (including nutritional supplements);
- body weight and lifestyle factors such as physical activity;
- smoking; and
- intake of aspirin and other non-steroidal anti-inflammatory drugs.
An Australian analysis estimated 10.1% of colon and 5.8% of rectum cancers diagnosed in 2010 were attributable to overweight and obesity. An estimated 2,614 cases of bowel cancers (18%) occurring in Australians in 2010 were attributable to red/processed meat consumption. A further 2,609 colorectal cancers (18% of colorectal) were attributable to insufficient fibre intake. Obesity, particularly “central obesity” (around the waist), is a risk factor for bowel cancer and adenomas, independent of other factors. See the Obesity, physical activity and nutrition chapter of the National Cancer Prevention Policy for more information.
A number of studies have also shown that smoking is a risk factor for bowel cancer and precancerous adenomas. An Australian report estimated that 6.4% of deaths from bowel cancer among both men and women were attributable to smoking. See the Tobacco control chapter of the National Cancer Prevention Policy for more information.
A report released by WCRF in 2018 found that consuming two or more alcoholic drinks per day increases the risk of bowel cancer. See the Alcohol chapter of the National Cancer Prevention Policy for more information.
Aspirin has been shown to significantly reduce bowel cancer in average risk populations; however, there are adverse effects. Findings from the Nurses’ Health Study  and the Women’s Health Study indicate that the benefit is not evident until after more than a decade of regular aspirin use. Adverse effects of aspirin include dyspepsia, peptic ulcer, bleeding diathesis and gastrointestinal haemorrhage. After reviewing research into the effects of aspirin and non-steroidal anti-inflammatory drugs (NSAIDs), the Colorectal Cancer Guidelines working party recommends aspirin be actively considered to prevent bowel cancer for those at an average risk of bowel cancer and NSAIDs used for individuals with familial adenomatous polyposis where surgery is inappropriate. See Council Australia’s Clinical Practice Guidelines on Colorectal Cancer.
Role of GPs in bowel cancer prevention
General practitioners (GPs) and their teams have an important role in bowel cancer prevention. As 86% of the Australian population see a GP every year, they “have enormous potential to encourage patients to take greater responsibility for their health.” Australian Doctor surveyed 1246 Australians in 2006, with 56% reporting they would act on advice from their GP in relation to lifestyle changes such as losing weight, quitting smoking and doing more exercise, all of which reduce the risk of bowel cancer.
The Royal College of General Practitioners has published two key documents to support cancer prevention in general practice: the Guidelines for preventive activities in general practice (the ‘red book’) listing who is most at risk, along with recommendations for cancer prevention and screening; and Putting prevention into practice: guidelines for the implementation of prevention in the general practice setting (the ‘green book’).
While there is evidence showing that GP interventions can help to prevent cancer, there are also barriers, including the lack of time in typical general practice consultations. Solutions could focus on: how to use this time most effectively; the role of e-health measures such as follow-up, recall, and desktop prompts; non-GP measures such as practice nurse involvement; and non-clinical staff measures such as utilising waiting room opportunities.
GPs also have a critical role to play in screening to prevent bowel cancer mortality and morbidity.
Implementation planning for the National Bowel Cancer Screening Program must include measures to formalise the involvement and provision of support to GPs.
Non-modifiable risk factors
Important bowel cancer risk factors that cannot be modified through lifestyle or behavioural change include a hereditary syndrome, personal or family history of bowel cancer and advanced adenoma or chronic inflammatory bowel disease.
Two specific syndromes, which both have a defined inherited genetic basis, are familial adenomatous polyposis and Lynch syndrome (previously known as hereditary non-polyposis colorectal cancer). Lynch Syndrome is also associated with an excess of cancers at other sites, including the endometrium and ovary. The Clinical Practice Guidelines for the Prevention, Early Detection and Management of Colorectal Cancer recommends clinical surveillance of individuals with these risk factors.
Greater adult attained height has been shown to be indirectly associated with increased risk of bowel cancer. Adult attained height is unlikely to directly influence cancer risk, and is more likely to be a marker for genetic, environmental, hormonal and nutritional factors affecting growth.
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