Taking antibiotics may be linked to a heightened risk of bowel cancer precursors, new research suggests.
A study found that long term antibiotic use in early to mid-life was linked to abnormal growths in the colon and rectum - known as polyps or colorectal adenomas - which precede the development of most cases of bowel cancer.
The findings add to emerging evidence that the type and diversity of bacteria in the gut, referred to as the ‘microbiome,’ may have a key role in the development of cancer, the researchers said.
In light of the findings, they’ve said there is a potential need to “limit the use of antibiotics”.
To draw their conclusions t research team drew on data from the Nurses Health Study. This has been monitoring the health of more than 120,000 US nurses who were all aged between 30 and 55 when they entered the study in 1976.
Since joining, study participants have filled in detailed questionnaires every two years on demographics, lifestyle factors, medical history and disease development, and every four years on their dietary habits.
For the purposes of the current study, analysis of the data was restricted to just over 16,000 women who were aged 60 and older in 2004, able to provide a history of antibiotic use between the ages of 20 and 59, and who had had at least one bowel investigation (colonoscopy) between 2004 and 2010.
During this period, 1195 adenomas were newly diagnosed in this group.
Recent use of antibiotics within the past four years wasn’t associated with a heightened risk of an adenoma diagnosis, but long term use in the past was.
Compared with those who hadn’t taken antibiotics for any extended period in their 20s and 30s, those who had taken them for two months or more were 36% more likely to be diagnosed with an adenoma, the researchers said.
This association held true irrespective of whether the adenoma was considered high or low risk for bowel cancer, but was stronger for growths located in the proximal, rather than the distal, colon.
The proximal colon refers to the caecum (pouch at the junction of the small and large intestines), ascending colon, hepatic flexure (the sharp bend between the ascending and transverse colon), transverse colon, and the splenic flexure (the sharp bend between the transverse colon and descending colon). The distal colon refers to the descending or sigmoid colon.
Similarly, women who had taken antibiotics for two months or more during their 40s and 50s were 69% more likely to be diagnosed with an adenoma than those who hadn’t taken these drugs for any extended period.
Once again, this association held true, irrespective of whether the adenoma was high or low risk for bowel cancer, and was more strongly linked to proximal colon adenomas.
Compared with women who had not been on antibiotics for any length of time from their 20s to their 50s, those who had taken these drugs for more than 15 days between the ages of 20 and 39, and between the ages of 40 and 59, were 73% more likely to be diagnosed with an adenoma.
The researchers pointed out this this is an observational study, so no firm conclusions can be drawn about cause and effect.
The researchers also didn’t gather information on the type or formulation of antibiotic taken and noted that some adenomas might have been present before antibiotics were used.
Nevertheless, there is a plausible biological explanation for the associations found, they suggested.
Antibiotics fundamentally alter the gut microbiome, by curbing the diversity and number of bacteria, and reducing resistance to ‘hostile’ bugs.
Previous research points to depletion of certain types of bacteria and an abundance of others in patients with bowel cancer.
This might all have a crucial role the development of bowel cancer, added to which the bugs that require antibiotics may induce inflammation, which is a known risk for the development of bowel cancer, the researchers said.
“The findings, if confirmed by other studies, suggest the potential need to limit the use of antibiotics and sources of inflammation that may drive tumour formation,” they concluded.
The research is published online in the journal Gut.