Colorectal cancer (defined as the cancer of the colon and rectum) is the second leading cause of cancer-related deaths in the United States and is responsible for about 55,000 deaths per year. According to the 2005 update, the American Cancer Society estimates the incidence of 149,000 new cases this year in the U.S.
Developing colorectal cancer, as with the case of any type of cancer, is a multi-step process. This means that there are multiple things that need to take place first before cancer occurs. These multiple steps can be brought about by either genetic or environmental factors.
Genetic factors are what lead to the hereditary occurrence of cancer. Hereditary cancer typically occurs at a relatively early age, and happens due to a defect or a mutation in an important gene, which is passed on from one generation to the next. For example, a mutation in a gene called APC can be passed on from one generation to the next and leads to a condition called Familial Adenoma Polyposis (FAP). These patients develop a large number of colon polyps, which can be precursors for developing colon cancer. This mutation does not necessarily guarantee that the individual will develop cancer, but it predisposes him/her to cancer.
There are many environmental factors that can predispose anyone (even when the individual does not inherit a mutation) to develop cancer. In the case of colorectal cancer, numerous epidemiological studies have linked the incidence of colorectal cancer with a diet high in red meat and animal fat and low in vegetables and fiber. This type of diet, unfortunately, has been labeled as the Western diet, which can explain the high number of colorectal cancer incidence in the Western world, particularly the United States.
This Western diet has been linked to an increase in the concentration of bile acids in people. A persistent increase in the levels of bile acids has been associated with an increase in risk and incidence of colon cancer.
What are bile acids?
Bile acids are synthesized in the liver from cholesterol, stored in the gallbladder, and released into the intestine to help the body digest and absorb fat. The problem occurs when a small percentage (about 4%) escape into the colon, where they are converted by colonic bacteria into “secondary” bile acids. These secondary bile acids (particularly deoxycholic acid or DCA for short) have been associated with an increase in risk and incidence of colon cancer.
How bile acids actually increase the risk of developing colon cancer is currently a hot research topic. The mechanisms by which DCA lead to the promotion of colon cancer remain largely unknown. Many research groups are studying the DCA-induced mechanisms, however, and many recent papers have attempted to explain these mechanisms. A summary of these papers will perhaps be the topic of another article. In addition, some studies are aimed at counteracting the effects of bile acids as tumor promoters. Much is yet to be done in this field to understand the mechanisms that are exploited by DCA and how to counteract these effects.
So what’s the bottom line?
The message here is the same one you’ve heard over and over. In order to decrease your risk of colon cancer: decrease intake of red meat and fat, and increase intake of fruits and vegetables. Over time, this will decrease the overall exposure of your colon to secondary bile acids, which will probably reduce your risk of developing colorectal cancer.
About the Author:
Sherif Morgan is a PhD student in Cancer Biology. His dissertation project is to elucidate the mechanisms by which bile acids, particularly deoxycholic acid, contribute to the development and progression of colorectal cancer. To learn more about Sherif Morgan, visit
SherifMorgan.com