A recent study finds out that antibiotic use is linked to the higher risk of developing bowel cancer. The findings, published online in the journal Gut conclude that there is an association between antibiotic use and an increase in colon cancer risk, but a decrease in rectal cancer risk.

According to the researchers, the findings suggest a pattern of risk that may be linked to differences in gut microbiome (bacteria) activity along the length of the bowel and reiterate the importance of judicious prescribing. Data shows that the people around the world took an estimated 70 billion doses of antibiotics in 2010, which is equivalent to ten doses each. The Antibiotics have a strong and long-lasting impact on the gut microbiome, altering the balance of helpful and harmful bacteria. So, the researchers decided to find out if this might affect bowel and rectal cancer risk and if yes, how. To investigate, they took data from the Clinical Practice Research Datalink from 1989–2012. This database carries the anonymized medical records of 11.3 million people from 674 doctor’s offices across the United Kingdom. From these, the researchers have extracted the data of 19,726 people of age group 40-90 who developed colon cancer and of 9,254 who developed rectal cancer. They have also collected the data of 137,077 patients, matched for age and sex, who didn’t develop these cancers. Later, they prescribed antibiotics to 70% (20,278) of patients with bowel and rectal cancers and 68.5% (93,862) of those without. Most of the patients had been given more than one class of antibiotics. The patients with bowel cancer were more likely to have been prescribed antibiotics: 71.5% vs 69%. Exposure levels were comparable among those who developed rectal cancer (67%).

The link between bowel cancer and antibiotic use was evident among patients who had taken these drugs for more than ten years before their cancer was diagnosed. Most of the patients who developed bowel cancer were more likely to have been prescribed antibiotics targeting anaerobes, which don’t need oxygen. Compared to them, patients with rectal cancer were less likely to have been prescribed antibiotics targeting aerobic bacteria.

The researchers have also focused on the pills and tablets and also the cancer site since science currently has limited understanding of the impact of intravenous antibiotics on gut bacteria. Cancer of the proximal colon (the first and middle parts of the bowel) was associated with the use of antibiotics targeting anaerobes compared to people without cancer. Antibiotic use was not associated with cancer of the distal colon — the last part of the bowel.

But, conversely, the researchers found an association between antibiotic use and a reduced risk of rectal cancer. The antibiotic use exceeding 60 days was associated with a 15% lower risk of rectal cancer.

Further investigation regarding individual classes of antibiotics found that penicillin was “strongly associated with increased colon cancer risk.” However, tetracyclines showed a reduced risk of rectal cancer.

Though the research has many strengths, the authors admit that there are certain limitations for the study. The researchers weren’t able to capture potentially influential lifestyle factors for all the participants, nor hospital treatment, which may have affected overall cancer risk.

However, the authors, as a conclusion say that “whether antibiotic exposure is causal or contributory to colon cancer risk, our results highlight the importance of judicious antibiotic use by clinicians.”

Source: Science Daily, Medical News Today.