Ask the Doctors

Dear Doctor: A new study said that prolonged antibiotic use is tied to colon polyps. But "prolonged" meant "two weeks or more." I had a couple of bacterial infections in a six-month timespan. How worried should I be?

Dear Reader: Antibiotics have undoubtedly revolutionized medicine, saving countless lives against multiple types of bacterial infections. However, with antibiotics readily available and a society that craves a quick fix, antibiotics have been overused. For example, they are often prescribed needlessly for upper respiratory symptoms that are not due to bacterial causes. Such overuse has led to the formation of antibiotic resistance; alterations of normal bacterial populations in the intestinal, oral and nasal cavities; and unnecessary side effects from the antibiotics themselves.

As for whether antibiotics can increase the risk of precancerous polyps in the colon, let's look at the evidence.

The study to which you're referring, published this year in the journal Gut, reviewed the antibiotic usage of 16,642 female nurses age 60 or older. In 2004, the women filled out a questionnaire reporting the amount of antibiotics they used between the ages of 20 and 39 and between the ages of 40 and 59. In 2008, the women filled out another questionnaire reporting their antibiotic usage between 2004 and 2008. All the women had at least one colonoscopy between 2004 and 2010.

Researchers found that women who took antibiotics between the ages of 20 and 39 had an increased risk of colon polyps compared to women who hadn't taken antibiotics. The increased risk was relatively small for women who had taken antibiotics for only one to 14 days within that 20-year period, but the risk increased significantly -- by about 1.4 times -- among women who took antibiotics for 14 days to two months. That heightened risk didn't increase further among women who took antibiotics for greater than two months.

For women who took antibiotics between ages 40 and 59, the rate of colon polyps increased more dramatically and was more dependent upon the length of antibiotic use. Those who took antibiotics for more than two months had a 1.69 times greater risk of developing colon polyps compared to women who hadn't taken antibiotics. Because colon polyps can eventually lead to colon cancer, the findings are worrisome.

Additionally worrisome are the findings of a 2008 Finnish study of people ages 30 to 79 assessing their antibiotic use from 1995 through 1997. The researchers found that people who had six or more prescriptions of antibiotics in that two-year timeframe had a 15 percent increased risk of colon cancer.

A possible theory about why antibiotics may lead to the formation of colon polyps, and later cancer, could be because they indiscriminately kill healthy gut bacteria. As this occurs, other, more unhealthy bacteria predominate in the colon, which can affect its immune response, leading to disruptions in its lining and the formation of polyps.

So, yes, there does appear to be some increased risk of colon polyps with antibiotic use. I wouldn't be overly concerned about two courses of antibiotics, though I would be concerned for a multitude of reasons about a repetitive use of antibiotics. Such use raises the need to look for new ways to prevent, and treat, infections.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

More like Ask the Doctors