Overuse of Antibiotics Linked to Colon Polyps

While antibiotics can be lifesaving — overuse of antibiotics may cause health problems, including possibly increasing the risk for precancerous colon polyps.

There’s no doubt antibiotics have saved the lives of millions of people by successfully treating serious bacterial infections, including strep and pneumonia. But antibiotics aren’t always harmless.

In addition to potential allergic reactions and side effects of antibiotics, they can upset your digestive system’s natural balance between “good” and “bad” bacteria.

In recent years, overuse of antibiotics has resulted in antibiotic resistance, too. What is antibiotic resistance? This serious and even dangerous problem is caused by bacteria evolving into increasingly difficult to treat drug-resistant strains. Scientists are also studying another potential downside to the overuse of antibiotics — the development of precancerous colon polyps in the colon.

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Polyps, small growths that develop on the lining of the colon or rectum, are most often benign. But some, a type called adenomas, can be precursors of colorectal cancer. That’s one reason colonoscopies are important. In addition to finding colon cancer at an early and more curable state, colonoscopies can find adenomas and allow doctors to remove them before they become cancerous.

While family history, and growing older increase the risk of adenomas, according to the American Cancer Society, some researchers think changes to the intestinal microbiome (the kinds of bacteria dwelling in the gastrointestinal tract) caused by prolonged use of antibiotics could be an important factor in the development of these precancerous polyps.

To investigate this possibility, Harvard University researchers studied data from the Nurses Health Study, a long term project monitoring the health of 121,700 nurses in the U.S. since l976. Since joining the study, the participants have answered detailed questions every four years about their diets and, every two years, they’ve provided information about their medical history, lifestyle, and any diseases they’ve developed.

The Harvard research team investigated this data on 16,642 women in the study. All were 60 years old or older and were able to verify any use of antibiotics from the time they were 20. Each of these research subjects had colonoscopies between 2004 and 2010 to check for cancer and polyps.

The results of the study showed almost 2,000 of the women had been diagnosed with adenomas. While recently taking antibiotics within the past four years wasn't associated with a heightened risk of these precancerous polyps, taking antibiotics for two months or longer in the past was.

In fact, the women who had taken the drugs long-term in their 20s and 30s, compared with women who did not take antibiotics during the same period, were 36 percent more likely to have been diagnosed with an adenoma. And women who had taken antibiotics for two months or more during their 40s and 50s were almost 70 percent more likely to have been diagnosed with an adenoma, compared with those who hadn't taken these drugs long term.

Although the study was a large one, it is doesn’t prove overuse of antibiotics or long-term use causes precancerous polyps — it shows only an association. The researchers did not have information on the specific types of antibiotics research participants took, and they have no way to know if the women had polyps before they ever used the drugs.

However, based on what scientists are learning about the importance of the gut microbiome, the study raises the possibility long-term antibiotic use may alter the balance between “good” and “bad” intestinal bacteria and trigger inflammation and the growth of adenomas — raising the risk for colon cancer.

"The findings, if confirmed by other studies, suggest the potential need to limit the use of antibiotics and sources of inflammation that may drive tumor formation," the researchers concluded.

If you need antibiotics, whether long-term or short-term, never stop taking them without talking to your doctor. But it’s also smart to do your part in preventing the overuse of antibiotics. For example, people often insist on antibiotics for viral infections, although viruses do not respond to antibiotics.

If you have risk factors for colon cancer, you can lower your risk by having colonoscopies at intervals suggested by your doctor and by getting regular exercise, keeping weight under control, and eating a fiber rich diet. Limiting or avoiding red and processed meats, eating more fruit and vegetables, and not drinking alcohol in excess may lower your risk, too, according to the American Cancer Society.

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