Boston—With the increasing use of antibiotics in the United States, researchers are raising questions about exposure to the drugs and heightened risk for illnesses such as inflammatory bowel disease, celiac disease, and even obesity.

A study published recently in the journal Gut suggests antibiotics could have a wide range of effects on the gut microbiota, which appear to play a role in colorectal cancer.

Massachusetts General Hospital and Harvard Medical School–led researchers sought to explore whether colorectal neoplasia actually could be promoted by antibiotic use and the subsequent effect on gut microbiota.

To that end, they focused on 16,642 women, aged 60 and older, enrolled in the Nurses’ Health Study who underwent at least one colonoscopy through 2010. Specifically, the research concentrated on the association between antibiotic use at ages 20 to 39 and 40 to 59 (as assessed in 2004), and recent antibiotic use (as assessed in 2008), with risk of subsequent colorectal adenoma.

Among the cohort, 1,195 cases of colorectal adenoma were documented, and the study authors further report that increasing duration of antibiotic use at ages 20 to 39 was significantly associated with an increased risk of developing adenomas. Results indicate that, compared with non-users, women who used antibiotics for more than 2 months between ages 20 and 39 had a multivariable odds ratio (OR) of 1.36, and that women who used the medications for 2 months or more between ages 40 and 59 had an even greater risk, with an OR of 1.69.

The researchers point out that the links were similar for low-risk vs. high-risk adenomas—defined as 1 cm or larger with tubulovillous/villous histology, or three or more detected lesions. The associations appeared modestly stronger, however, for proximal, compared with distal, adenomas.

On the other hand, recent antibiotic use within the past 4 years was not associated with risk of adenoma, according to the report.

“Long-term antibiotic use in early-to-middle adulthood was associated with increased risk of colorectal adenoma,” the study authors conclude.

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