People who take antibiotics for two months or longer during their working life are more likely to develop bowel growths that can become cancerous, a new study has found.
By analysing a major study into the health of US nurses, researchers found those who had taken antibiotics for a long time between the ages of 20 and 39 were more likely to be diagnosed with a particular type of bowel polyp later in life.
Bowel polyps, small growths on the inner lining of the colon or rectum, affect 15 to 20 per cent of people in the UK and are usually harmless but sometimes develop into cancer.
The researchers said the findings add weight to emerging evidence that the type and diversity of bacteria in the gut may have a key role in the development of the disease.
However they did not look at how many of the polyps, known as adenomas, did go on to become cancerous.
The research, published in the journal Gut, examined data from 16,642 women who had taken part in the Nurses Health Study, set up to monitor the health of 121,700 nurses.
Since joining the study in 1976, the nurses have filled in detailed questionnaires every two years about aspects of their life, including lifestyle factors, medical history and disease development.
The subjects of the new research were aged 60 and older in 2004, were able to provide a history of antibiotic use between the ages of 20 and 59 and had had at least one bowel investigation between 2004 and 2010.
During this period, 1,195 abnormal growths in the colon and rectum were diagnosed in this group. Adenomas precede the development of the majority of cases of bowel cancer.
The researchers found that recent use of antibiotics within the past four years was not associated with a heightened risk of an adenoma diagnosis, but long-term use in the past was.
Those who had taken antibiotics for two months or more between the ages of 20 and 39 were 36 per cent more likely to be diagnosed with an adenoma when compared with those who had not taken antibiotics for any extended period in their twenties and thirties.
Similarly, women who had taken antibiotics for two months or more during their forties and fifties were 69 per cent more likely to be diagnosed with an adenoma than those who had not taken such medication for an extended period.
And those who had taken these drugs for 15 days or more between the ages of 20 and 39, and between the ages of 40 and 59, were 73 per cent more likely to be diagnosed with an adenoma, when compared to non-users.
The authors wrote: “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.”
Sheena Cruickshank, senior lecturer in immunology at the University of Manchester, said while “there is increasing evidence that our microbiota are important in regulating our immune responses and many aspects of our normal functions”, she would be concerned about advising people to avoid using antibiotics.
Additional reporting from Press Association
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