It has been estimated that about half of<unk>  cases are due to lifestyle factors, and about a quarter of all cases are preventable. Increasing surveillance, engaging in physical activity, consuming a diet high in fiber, and reducing smoking and alcohol consumption decrease the risk. Lifestyle Lifestyle risk factors with strong evidence include lack of exercise, cigarette smoking, alcohol, and obesity. The risk of colon<unk>  can be reduced by maintaining a normal body weight through a combination of sufficient exercise and eating a healthy diet. Current research consistently links eating more red meat and processed meat to a higher risk of the disease. Starting in the 1970s, dietary recommendations to prevent<unk>  often included increasing the consumption of whole grains, fruits and vegetables, and reducing the intake of red meat and processed meats. This was based on animal studies and retrospective observational studies. However, large scale prospective studies have failed to demonstrate a significant protective effect, and due to the multiple causes of<unk>  and the complexity of studying correlations between diet and health, it is uncertain whether any specific dietary interventions (outside of eating a healthy diet) will have significant protective effects. In 2018 the National<unk>  Institute stated that "There is no reliable evidence that a diet started in adulthood that is low in fat and meat and high in fiber, fruits, and vegetables reduces the risk of<unk>  by a clinically important degree." According to the World<unk>  Research Fund, consuming alcohol drinks and consuming processed meat both increase the risk of<unk>  With regard to dietary fiber, the 2014 World Health Organization<unk>  report noted that it has been hypothesized that fiber might help prevent<unk> , but most studies have not borne this out, and status of the science remained unclear as of 2014. A 2019 review, however, found evidence of benefit from dietary fiber and whole grains. The World<unk>  Research Fund listed the benefit of fiber for prevention of<unk>  as "probable" as of 2017. Higher physical activity is recommended. Physical exercise is associated with a modest reduction in colon but not rectal<unk>  risk. High levels of physical activity reduce the risk of colon<unk>  by about 21%. Sitting regularly for prolonged periods is associated with higher mortality from colon<unk> . The risk is not negated by regular exercise, though it is lowered. Medication and supplements Aspirin and celecoxib appear to decrease the risk of<unk>  in those at high risk. Aspirin is recommended in those who are 50 to 60 years old, do not have an increased risk of bleeding, and are at risk for cardiovascular disease to prevent<unk> . It is not recommended in those at average risk. There is tentative evidence for calcium supplementation, but it is not sufficient to make a recommendation. Vitamin D intake and blood levels are associated with a lower risk of colon<unk> . Screening As more than 80% of<unk> s arise from adenomatous polyps, screening for this<unk>  is effective for both early detection and for prevention. Diagnosis of cases of<unk>  through screening tends to occur 2–3 years before diagnosis of cases with symptoms. Any polyps that are detected can be removed, usually by colonoscopy or sigmoidoscopy, and thus prevent them from turning into<unk> . Screening has the potential to reduce<unk>  deaths by 60%. The three main screening tests are colonoscopy, fecal occult blood testing, and flexible sigmoidoscopy. Of the three, only sigmoidoscopy cannot screen the right side of the colon where 42% of<unk> s are found. Flexible sigmoidoscopy, however, has the best evidence for decreasing the risk of death from any cause. Fecal occult blood testing (FOBT) of the stool is typically recommended every two years and can be either guaiac-based or immunochemical. If abnormal FOBT results are found, participants are typically referred for a follow-up colonoscopy examination. When done once every 1–2 years, FOBT screening reduces<unk>  deaths by 16% and among those participating in screening,<unk>  deaths can be reduced up to 23%, although it has not been proven to reduce all-cause mortality. Immunochemical tests are accurate and do not require dietary or medication changes before testing. Other options include virtual colonoscopy and stool DNA screening testing (FIT-DNA). Virtual colonoscopy via a CT scan appears as good as standard colonoscopy for detecting<unk> s and large adenomas but is expensive, associated with radiation exposure, and cannot remove any detected abnormal growths as standard colonoscopy can. Stool DNA screening test looks for biomarkers associated with<unk>  and precancerous lesions, including altered DNA and blood hemoglobin. A positive result should be followed by colonoscopy. FIT-DNA has more false positives than FIT and thus results in more adverse effects. Further study is required as of 2016 to determine whether a three-year screening interval is correct. Recommendations In the United States, screening is typically recommended between ages 50 to 75 years. The American<unk>  Society recommends starting at the age of 45. For those between 76 and 85 years old, the decision to screen should be individualized. For those at high risk, screenings usually begin at around 40. Several screening methods are recommended including stool-based tests every 2 years, sigmoidoscopy every 10 years with fecal immunochemical testing every two years, and colonoscopy every 10 years. It is unclear which of these two methods is better. Colonoscopy may find more<unk> s in the first part of the colon, but is associated with greater cost and more complications. For people with average risk who have had a high-quality colonoscopy with normal results, the American Gastroenterological Association does not recommend any type of screening in the 10 years following the colonoscopy. For people over 75 or those with a life expectancy of less than 10 years, screening is not recommended. It takes about 10 years after screening for one out of a 1000 people to benefit. The USPSTF list seven potential strategies for screening, with the most important thing being that at least one of these strategies is appropriately used. In Canada, among those 50 to 75 years old at normal risk, fecal immunochemical testing or FOBT is recommended every two years or sigmoidoscopy every 10 years. Colonoscopy is less preferred. Some countries have national<unk>  screening programs which offer FOBT screening for all adults within a certain age group, typically starting between ages 50 to 60. Examples of countries with organised screening include the United Kingdom, Australia, the Netherlands, Hong Kong and Taiwan.
Colorectal cancer
Irritable bowel syndrome
Anal cancer
Gastrointestinal cancer
Pancreatic cancer
Small intestine cancer
Colitis
Liver cancer