TAKING antibiotics could increase the risk of developing colon cancer by as much as half in the under-50s, scientists have found, with older people also seeing a higher risk from taking them.

For the first time, while the numbers remain low, scientists showed antibiotic use was linked with an estimated 50% higher risk of colon cancer in people aged under 50, and an estimated 9% higher risk in those 50 and over.

Sarah Perrott, of the University of Aberdeen and co-first author of the new paper, said: “We found antibiotic exposure was associated with colon cancer among all age groups.

“This, along with multiple other dietary and lifestyle factors, may be contributing to increased cases of colon cancer among young people.”

She added: “Antibiotic use is very common, and it is important to note that not everyone who uses antibiotics will get bowel cancer.”

Scientists from the University of Aberdeen, NHS Grampian and Queen’s University Belfast, looked at 40,000 people and compared antibiotic use and lifestyle factors of those who had cancer and those who didn’t.

While no relationship was found with rectal cancer, antibiotic use was found to be associated with the development of colon cancer.

Both colon and rectal cancer affect the large intestine.

The study did not determine a threshold dose, but the risk appeared to be the same after minimal exposure to antibiotics, said Perrot.

According to the paper, which has been published in the British Journal of Cancer, the reasons behind the link are thought to be because of the impact of antibiotics on the bacteria within the gut microbiome, which can lead to altered bacterial activity and interfere with normal immune function.

This can lead to chronic inflammation and, theoretically, increase the risk of cancer.

Perrott said antibiotics had a “detrimental impact on the gut microbiota” and they can lead to “permanent changes to the natural gut environment”.

“It is important to note that diet, lifestyle, stress, and so many different factors can affect gut health and antibiotic use is just one of those factors,” she added.

Scientists said that prescribing of antibiotics should be considered carefully and when there are probiotic supplements could be useful to counteract the negative effects of the drugs.

Dr Leslie Samuel, senior author and consultant GI oncologist at NHS Grampian, said doctors were seeing more patients under 50 with the cancer, many of whom do not have expected factors like high alcohol intake or diabetes.

“The gut microbiome comprises a delicate balance of bacteria and disruption to that – be it from lifestyle factors or from repeated use of antibiotics as we have seen here, can have very serious consequences,” said Dr Samuel.

Alice Davies, from Cancer Research UK, said: “Currently, there isn’t enough evidence to say if antibiotics are definitely increasing people’s risk, but this gives us another piece of the puzzle.”

Previously, only a small number of studies investigating an antibiotic and colon cancer link existed and these studies were limited to older adults and showed mixed results.