Long term antibiotic usage increases risk of cancer-inducing polyps growth

Researchers drew data by monitoring health of 121,700 nurses who were all aged between 30-55

Long term use of antibiotics increases the risk of abnormal growths in the colon — known as polyps — that can lead to bowel cancer, researchers said on Wednesday.

Researchers, including those from Harvard University in the US, drew on data monitoring the health of 121,700 nurses who were all aged between 30 and 55 when they entered the study in 1976.

Study participants filled in detailed questionnaires every two years on demographics, lifestyle factors, medical history and disease development, and every four years on their dietary habits.

Analysis of the data was restricted to about 16,642 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 colonoscopy between 2004 and 2010.

Researchers found 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.

Compared with those who had not taken antibiotics for any extended period in their 20s and 30s, those who had taken them for two months or more were 36 per cent more likely to be diagnosed with an adenoma.

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, researchers said.

Similarly, women who had taken antibiotics for two months or more during their 40s and 50s were 69 per cent more likely to be diagnosed with an adenoma than those who had not taken these drugs for any extended period.

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 per cent more likely to be diagnosed with an adenoma.

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, 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," said Yin Cao of Harvard University.

The study was published in the journal Gut.