11 Causes of Colon Cancer

Understanding the Risk Factors Allows for Early Diagnosis

A woman smoking a cigarette, one of the causes of colon cancer
Sabina Dimitriu/Getty Images

Colon cancer is the third leading cause of cancer-related deaths in the U.S. in both men and women. All told, around five percent of American men and women will experience colon or rectal cancer in the course of their lifetime, and 30 percent will die as a result of the disease. This doesn't have to happen. Knowing the causes and your risk factors for colon cancer can help you understand the importance of routine screening, as well as learn if you are one of the people who should begin screening at an earlier age.

The earlier a colon cancer is diagnosed, the greater the chance for a cure. That said, far too many people are diagnosed only after their cancer has already spread and a cure is no longer possible.

While there has been some controversy over cancer screening tests in the United States, this is not the case with colon cancer. Screening (with a colonoscopy at age 50, and earlier for some people) can save lives. In addition, colon cancer screening is unique among cancer screening tests. It can be used for early detection, that is, finding cancer in the earliest stage possible, but can also be used for prevention. When a precancerous polyp is found on exam, it can be removed before it ever has the opportunity to become cancerous.

Top Causes of Colon Cancer

As we talk about the causes of colon cancer, consider your own risk. Some people should be screened long before the recommended age of 50. And keep in mind that, even though family history is a risk factor for colon cancer, the majority of people who develop the disease do not have a family history.

In other words, everybody needs to be screened. Here are some causes of colon cancer that everyone should know.

1. Age and Aging

Age is the number one risk factor for colon cancer with 81 percent of cases occurring in people over the age of 45. Of these, more than 65 percent of cancer will be in people between the ages of 65 and 84.

2. Alcohol Consumption

Alcohol is now considered one of the major risk factors for colorectal cancer, and the risk is directly linked to the amount of alcohol consumed. It is thought that even moderate alcohol consumption can put a person at risk, and several mechanisms for this relationship are being evaluated. It's not only colon cancer, however, and alcohol has been found to be a  risk factor for other cancers as well. These include liver cancer, oral cancer, breast cancer, throat cancer, esophageal cancer, and laryngeal cancer.

3. Diabetes Risk

Several studies have now confirmed a link between diabetes (type I and type II) and the development of colon cancer. People with diabetes may be up to 40 percent more likely to develop colon cancer than people without the disease. Other studies have found that the link is independent of diet.

4. Dietary Factors

Diets high in fat and cholesterol, especially from animal sources, have been linked to colon cancer. It's thought that high-fat foods can change normal cells into stem cells, which they have the potential to convert into tumors. A diet low in fiber, fruits, and vegetables is also associated with an increased risk.

5. Ethnicity and Race

Ethnicity is also a well-known factor associated with cancer risk.

African Americans, for example, have a 40 percent greater chance of colon cancer than whites, as well as a 20 percent greater risk of death. By contrast, Asians are known to be at lower risk when compared to all other groups.

6. Family History of Colon Cancer

If you have had a relative who had colon cancer, your chance of getting the disease is automatically increased. If it's a first-degree relative (a parent, sibling, or offspring), your risk can double and even triple in some cases.

7. Genetic Factors

Research has shown that one in four cases of colon cancer has some sort of genetic link. The most common hereditary causes include genetic mutations associated with the development of FAP (familial adenomatous polyposis) and HNPCC (hereditary non-polyposis colorectal cancer or Lynch syndrome).

8. Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is characterized by conditions such as ulcerative colitis and Crohn's disease. Both are associated with the development of colorectal cancer. Generally speaking, the longer a person has had IBD, the greater his or her chance of developing colon cancer.

9. Obesity and Cancer Risk

The link between colon cancer and obesity is strong. All told, people who are obese are over 30 percent more likely to develop this type of cancer than people of normal weight

10. Precancerous Polyps

A colon polyp is a small clump of cells that forms on the lining of the colon. Virtually all colon cancers develop from non-cancerous adenomatous polyps that that are similar in structure to normal tissues but can become malignant as they grow in size. When these polyps are found, and removed via colonoscopy, they no longer have the opportunity to transform from precancerous to cancerous.

11. Smoking Risk

We all know that cigarettes can cause damage to every organ system of the body. In terms of colon cancer, long-term smoking is associated the accelerated polyp growth as well the delivery of carcinogens to the mucosal tissues of the colon. These together create a perfect storm for cancer.

Bottom Line on Colon Cancer Causes

Becoming familiar with the possible causes and risk factors for colon cancer is an excellent way of becoming your own advocate for your health. We know that one in two men and one in three women will develop cancer during their lifetime. Of cancers, colon cancer is the third leading killer of both sexes. 

Some risk factors can be modified, but others can't. That said, we have an excellent method of either finding or preventing colon cancer from occurring in the first place. It's likely we could drastically reduce the number of colon cancer deaths in the United States if two things were to occur. Number one, if everyone would receive screening at the age of 50. Number two, if everyone with an elevated risk (by knowing their risk factors) talks to their doctors about screening at a younger age.

Now that you have a handle on what causes colon cancer, learn the top 10 ways to prevent the disease whether you consider yourself at risk or not.


Centers for Disease Control and Prevention. Risk Factors for Colorectal Cancer. Updated 04/25/16. https://www.cdc.gov/cancer/colorectal/basic_info/risk_factors.htm

Rossi, M., Jahanzaib Anwar, M., Usman, A. et al. Colorectal Cancer and Alcohol Consumption—Populations to Molecules. Cances. 2018. 10(2):pii:E38.