TUESDAY, April 4, 2017 (HealthDay News) -- Taking antibiotics for an extended period in early to middle adulthood might increase your risk for precancerous growths in your colon, a large study suggests.
Women who took antibiotics for two months or more in their 20s through their 50s were more likely to have colon lesions in their 60s than women who didn't take the drugs for an extended period, researchers found.
If not removed, these lesions -- called polyps or adenomas -- can lead to colon cancer.
"This suggests that alterations in the naturally occurring bacteria that live in one's intestines caused by antibiotics might predispose individuals to colorectal cancer," said lead researcher Dr. Andrew Chan.
But, although the risk for colon cancer was raised, it wasn't to a level "where it should worry individuals who need to take antibiotics for clear medical reasons," said Chan, an associate professor of medicine at Harvard Medical School.
He also cautioned that this study cannot prove that long-term antibiotic use was the cause of the polyps, only that the two seem to be associated.
And, though the study was limited to women, the link likely also holds true for men, Chan said.
"More research needs to be done to understand the interaction between alterations in one's gut bacteria and future risk of colorectal cancer," he said.
Antibiotics disrupt the diversity and number of bacteria in the gut, or "microbiome." They also reduce resistance to toxic bacteria. All of this might play a role in the development of precancerous growths, Chan said.
In addition, bacteria that require antibiotics may cause inflammation, which is a known risk for colon cancer, he added.
For the report, Chan and his colleagues collected data on more than 16,600 women 60 and older who took part in the Nurses Health Study.
The women provided a history of antibiotic use between ages 20 and 59. They also had had at least one colonoscopy between 2004 and 2010. Nearly 1,200 precancerous polyps in the colon were found during that time.
Use of antibiotics within the previous four years wasn't associated with a heightened risk of polyps, but long-term use in the past was, Chan said.
For example, two months of antibiotic use in her 20s or 30s upped a woman's odds for polyps 36 percent compared to those who didn't the drugs for a prolonged period. The risk rose further when the extended medication use occurred in one's 40s or 50s, researchers found.
Shorter-term use wasn't without risk, either. Taking antibiotics for more than 15 days between ages 20 and 59 also increased the chances of finding polyps, the study found.
One New York City specialist agreed that bacterial changes in the gut wrought by antibiotics may up the odds for colon cancer.
"The biological plausibility of these findings may be explained by changes in the bacterial diversity of the colon after exposure to antibiotics, said Dr. Patrick Okolo, chief of gastroenterology at Lenox Hill Hospital.
This adds to the increasing evidence that gut bacteria may be important in human health, he said.
"Further research to determine cause and to examine nuances will be important in determining the full extent of these findings as well as their veracity," Okolo said.
Chan and his team acknowledged the study had limitations. For one, there was no information on the types of antibiotics used. Also, it's possible that some growths existed before antibiotics were taken, the researchers said.
The report was published online April 4 in the medical journal Gut.
Visit the American Cancer Society for more on colon cancer.