Colorectal cancer prevention: what role does lifestyle play??

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There is no shortage of advice on how to prevent colorectal cancer: more fiber, less meat, extra vitamins and even medications are on a long list of recommendations. The question is: How well are the most common claims scientifically proven?

Healthy people can reduce their risk of colorectal cancer by taking advantage of colorectal cancer screening. The studies are offered to all people over the age of 50 and have been shown to reduce the risk of colorectal cancer.

A healthy lifestyle is also thought to prevent colorectal cancer. But what is to be made of the numerous pieces of advice, especially on diet?? Does it really help to eat lots of vegetables and fruit and as little red meat as possible? And does it help to take additional vitamins??

Why are studies on the influence of lifestyle often unreliable?? Information on $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

Many assumptions about the relationship between lifestyle and health come from so-called observational studies. These studies can be structured in different ways. In the best case, healthy people document their lifestyle habits over a long period of time. After many years, it is then possible to determine, for example, whether people with certain dietary habits are more likely to develop colorectal cancer than others.

If one then observes that people who frequently eat red meat, for example, develop colorectal cancer more often than people who hardly ever eat red meat, it is reasonable to assume that eating red meat may promote colorectal cancer. However, it is also conceivable that people who eat a lot of red meat also smoke more often, drink more alcohol or are overweight more often – all factors that promote certain types of cancer. In theory, you can account for such confounding factors when evaluating a study. The problem, however, is that people also differ from each other in other aspects that are not or not readily apparent, such as their genes, working conditions and living arrangements. To take all this into account in a study is practically impossible. It also requires knowing all the factors associated with colorectal cancer and being able to measure them. Therefore, in observational studies, there is always the possibility that something important has been overlooked.

To find out the real cause of something, so-called randomized controlled trials are more appropriate. In such studies, volunteers are randomly divided into two groups (randomized). One of the groups is then encouraged to eat a diet low in red meat, for example, while the other group continues to eat as usual. The randomization principle ensures that the two groups are really comparable with each other. For chance not only ensures that, for example, men and women, old and young, or smokers and non-smokers are evenly distributed between the two groups. Even unknown influencing factors are thus similar in both groups.

However, this method is rarely used in lifestyle studies. Therefore, study results and lifestyle recommendations must often be viewed with skepticism. How unreliable such research results are is also shown by the fact that, for example, dietary recommendations change again and again.

Protect dietary fiber? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

Dietary fiber is a food component that usually consists of carbohydrates and cannot be digested by the body. They are generally considered to have a health-promoting effect. There are several theories about why dietary fiber might protect against colorectal cancer. Among other things, they speed up the transport of stool through the intestine and possibly bind cancer-promoting substances that are ingested with food.

Observational studies suggest an association between high-fiber diets and colorectal cancer: People who eat higher fiber diets appear to be slightly less likely to develop colorectal cancer. However, this has not been confirmed in randomized controlled trials: Some of these studies have examined whether eating more fiber protects against colorectal cancer. These studies showed no difference. However, because many people ended their participation in the studies prematurely, these results are also uncertain.

Can fruits and vegetables prevent colon cancer? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

Fruits and vegetables contain flavonoids, also known as secondary plant compounds. They are thought to have a cancer-preventing effect. One theory is that they protect against molecules that can damage cells, called free radicals. Flavonoids are also found in plant seeds and sprouts, tea, cocoa, chocolate and wine.

A group of scientists from the international research network Cochrane Collaboration evaluated several randomized trials that investigated the relationship between a flavonoid-rich diet and colorectal cancer. However, it found no convincing evidence that people who eat a lot of fruits and vegetables are less likely to develop colorectal cancer.

What is the truth of the warning about red and processed meat? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

Foods thought to be more likely to promote colorectal cancer include red meat and processed meat products such as sausage, cured or smoked meat. Some observational studies show a correlation: the more beef, lamb, or processed meat people eat, the more likely they are to develop colorectal cancer. According to current knowledge, this does not apply to unprocessed poultry and pork meat. There are no randomized trials to date that show that eating less red and processed meat protects against colorectal cancer.

Can being overweight increase the risk of colon cancer? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

A body mass index ( BMI ) between 25 and 30 is considered overweight. It is possible that men who are overweight have a slightly increased risk of colorectal cancer; in women, overweight does not play a major role. Looking at health in general, it is doubtful that moderate overweight is harmful. Whether losing some weight could protect against colorectal cancer cannot be inferred from studies to date.

The situation is different for men and women who are heavily overweight (obesity): From a BMI above 30, the risk of colorectal cancer increases significantly – and the higher the weight, the greater the risk. However, there are no randomized trials on the question of whether weight loss can reduce the risk of colorectal cancer in severely overweight people.

Does exercise protect against colorectal cancer? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

People who are more physically active appear to have a lower risk of colorectal cancer. But how exercise affects the risk of colorectal cancer has not yet been studied in randomized trials. Whether more exercise actually protects against colorectal cancer is therefore unclear.

Being physically active, however, makes many people feel better, improves fitness, and has other health benefits.

What role does alcohol play in colorectal cancer? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

Studies show a link between alcohol and colorectal cancer: the more alcohol a person drinks, the higher the risk of developing colorectal cancer.

But even independent of the influence of alcohol consumption on colorectal cancer risk, there are many good reasons to drink alcohol only in moderation. Excessive alcohol consumption usually has many health, psychological and social consequences, such as problems in partnerships and families or at work. Too much alcohol can also permanently damage the liver. In addition, psychological problems and illnesses such as depression can be exacerbated. Last but not least, it increases the risk of accidents, falls and injuries.

The German Centre for Addiction Issues recommends that healthy adults without an alcohol problem should not drink alcohol on at least two days a week. For low-risk alcohol consumption, different recommendations apply to men and women.

Does smoking increase the risk of colorectal cancer? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

Not smoking is one of the best things you can do for your health. People who smoke have a much higher risk of many types of cancer, especially lung, throat and larynx cancer. Smoking is a common cause of chronic lung disease and promotes many other diseases, such as those of the cardiovascular system . The risk of colorectal cancer is also slightly higher in people who smoke. However, the connection is much weaker than, for example, in the case of lung cancer.

What is known about dietary supplements? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

If you believe the advertising, dietary supplements have all kinds of beneficial effects on health. However, there is a valid reason to take dietary supplements only in case of malnutrition – or if they are used to treat a disease. And even then, it should be checked whether the remedies actually protect against diseases or alleviate complaints.

Many dietary supplements have been studied in randomized trials for protection against colorectal cancer: including calcium , folic acid , selenium and vitamins A, C, D and E. Not all are equally well studied. What is clear, however, is that none of these agents has yet been shown to protect against colorectal cancer. Some studies even suggest that certain supplements could increase the risk of colorectal cancer or cancer in general, or shorten life expectancy. Shown a possible harmful effect for high dosages of:

  • Vitamin A
  • Vitamin E
  • Beta-carotene
  • Folic acid supplements

However, the study results should not be misunderstood: The body needs vitamins and minerals and normally gets them through a balanced diet. If this is not the case or if there is an increased need in certain life situations (such as for folic acid before and during pregnancy), a dietary supplement can be useful.

However, a permanent overdose with certain dietary supplements without a concrete reason could be risky.

Are there drugs that can protect against colorectal cancer? Information on $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

Certain medicines are sometimes thought to be protective against colorectal cancer. However, the use of drugs to prevent cancer is tricky: To provide protection, they must be taken regularly over a very long period of time, possibly decades. This also increases the risk of side effects.

Medications that might lower the risk of colorectal cancer include acetylsalicylic acid ( ASA ). This drug is often used for pain or as a blood thinner. In studies on the prevention of secondary diseases in people with heart disease, it has been observed that ASA also appears to provide some protection against colorectal cancer. However, few studies have been designed to investigate this specifically. Therefore, a conclusive evaluation of the benefits is still difficult to. It is clear that the drug must be taken for at least ten years to have any preventive effect at all.

The side effects of ASA include stomach ulcers and bleeding, especially in the gastrointestinal tract. The scientific societies in Germany and other countries are so far against the use of ASA for the prevention of colorectal cancer.

What can I do in general to prevent colorectal cancer?? Information about $CMS_IF( ! tt_headline.isEmpty)$$CMS_VALUE(tt_headline.toText(false).convert2)$$CMS_END_IF$

For people without certain risk factors, the probability of developing colorectal cancer is not particularly high. The question of whether changing one’s lifestyle and diet or taking medications can reduce risk cannot be answered with certainty. Certain dietary supplements may actually do harm.

The best way to prevent colorectal cancer is through colorectal cancer screening. Two tests are offered for this purpose: the stool test and colonoscopy.

German Society for Gastroenterology, Digestive and Metabolic Diseases (DGVS). S3 Guideline Colorectal Cancer . AWMF Register No.: 021-007OL. 2019.

Jin H, Leng Q, Li C. Dietary flavonoid for preventing colorectal neoplasms . Cochrane Database Syst Rev 2012; (8): CD009350.

Vinceti M, Filippini T, Del Giovane C et al. Selenium for preventing cancer . Cochrane Database Syst Rev 2018; (1): CD005195.

Yao Y, Suo T, Andersson R et al. Dietary fiber for the prevention of recurrent colorectal adenomas and carcinomas . Cochrane Database Syst Rev 2017; (1): CD003430.

IQWiG health information is intended to help people understand the advantages and disadvantages of important treatment options and health care services.

Whether one of the options we describe is actually useful in a particular case can be clarified in a discussion with a health care professional. Health can support, but not replace, discussion with physicians and other professionals. We do not offer individual advice.

Our information is based on the results of high-quality studies. They are written by a team of authors from the medical, scientific and editorial communities and peer-reviewed by experts outside IQWiG. We describe in detail how we develop our texts and keep them up to date in our methods .

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