Long-term antibiotic use in early-to-middle adulthood is associated with an increased risk of colorectal adenoma, according to a study published in Gut.

Yin Cao, ScD, from the Clinical and Translational Epidemiology Unit at Massachusetts General Hospital and Harvard Medical School in Boston, and colleagues evaluated the association between antibiotic use at ages 20 to 39 and 40 to 59 (assessed in 2004) and recent antibiotic use (assessed in 2008) with risk of subsequent colorectal adenoma. A total of 16,642 women, enrolled in the Nurses’ Health Study, aged 60 or older who underwent at least one colonoscopy through 2010 were evaluated. A total of 1195 cases of adenoma were documented among the women evaluated.

Increasing duration of antibiotic use at ages 20 to 39 and 40 to 59 was significantly associated with an increased risk of colorectal adenoma. Compared with nonusers, women who used antibiotics for >2 months between ages 20 and 39 had a multivariable odds ratio (OR) of 1.36. Women who used >2 months of antibiotics between age 40 and 59 had a multivariable OR of 1.69.

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The associations were similar for low-risk vs high-risk adenomas (size >1 cm, or with tubulovillous/villous histology, or >3 detected lesions), but appeared stronger for proximal compared with distal adenomas. In contrast, recent antibiotic use within the past four years was not associated with risk of adenoma.


  1. Cao Y, Wu K, Mehta R, et al. Long-term use of antibiotics and risk of colorectal adenoma. Gut. 4 April 2017. doi: 10.1136/gutjnl-2016-313413