Long-term antibiotic users are more likely to develop adenomas, or bowel polyps, a common and usually benign growth that can lead to cancer.
A study published in the journal Gut found that study volunteers who had taken antibiotics for more than two months in their 20s and 30s were more likely to develop polyps in later life — that is, they had a 36 per cent greater likelihood of developing them.
The risk rose further in those who used the drugs for more than two months in their 40s and 50s.
Bowel polyps affect an estimated 15 to 20 per cent of the British population. Although fewer than 10 per cent of adenomas become cancerous, more than 95 per cent of colorectal cancers develop from adenomas.
This was not a clinical trial, and the study’s authors, from Harvard Medical School in the US, acknowledge that they have not established causality.
Writing in the journal, the authors said: ‘Antibiotics fundamentally alter the gut microbiome, by curbing the diversity and number of bacteria, and reducing the resistance to hostile bugs.
‘This might all have a crucial role in 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 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.’
There are several important caveats with this study. Firstly it is related to long-term antibiotic use rather than recurrent or one-off courses of antibiotics. It also studies the connection between their use and colorectal adenoma, and does not examine how many of these adenomas subsequently resulted in cancer. So the link is somewhat tenuous.
However, we are increasingly becoming more aware that overuse of antibiotics can cause many other problems, and we should already be extremely wary of using them unless we need to. That being said, infections which need to be treated with antibiotics can also have serious consequences if left untreated, so as always the pros and cons must be carefully considered.