Given the widespread use of antibiotics, it’s important to clear up their effects on gut microbiota and the links with health outcomes. With the increasing occurrence of antibiotic resistance, doctors are more cognisant of limiting the use of these drugs.

 

A recent study found a complex relationship between antibiotics and cancer risk. According to the study, there is an association between antibiotic use and an increase in colon cancer risk, but a decrease in rectal cancer risk.

 

The use of antibiotics kills and affects the structure of gut bacteria which are important in maintaining good health. Therefore, antibiotics have the potential to make a lasting impact on human health.

 

Globally, the consumption of antibiotics continues to grow annually. Researchers have deemed it necessary to understand better, the impact of antibiotics on human health.

 

The Aim of the Research

Several studies have suggested an antibiotic-cancer association. The scientists hypothesised that antibiotic use, which targets the gut microbiota, had an association with colorectal cancer initiation and progression. They explored whether these effects differed by anatomical location.

 

The current study which appears in the journal Gut was “to investigate the associations between antibiotic use and site-specific colorectal cancer risk in the world’s largest primary care database.”

 

They took data from the Clinical Practice Research Datalink from 1989–2012. This database carries the anonymised medical records of 11.3 million people from 674 doctor’s offices across the United Kingdom. The records contain detailed information of the drugs prescribed by doctors, including the dosage, instructions and quantity.

 

The scientists focused on oral antibiotics due to the limited understanding of the impact of intravenous antibiotics on gut bacteria. Also, they classified the antibiotics based on their effects on aerobes/anaerobes, and by drug class (such as penicillins, quinolones, and tetracyclines).

 

Participants had a median follow-up of 8.1 years. During this time, about 70% in the colon cancer group and 68.5% in the control group had taken antibiotics.

 

At the end of the research, they established an association between colon cancer risk and any antibiotic use.

“Participants who subsequently developed colon cancers were more likely to be exposed to antibiotics as compared with controls (71.3% versus 69.1%).”

 

In addition, they also found that “the effect, size and pattern of risk varied by anatomical location”. The effect was strongest for cancer in the proximal colon.

 

Additional Findings

However, surprisingly, the scientists found an association between antibiotic use and a reduced risk of rectal cancer which appears stronger for longer exposures to antibiotics. Precisely, the study showed a link between antibiotics use for over 60 days and a 15% reduction in the risk of rectal cancer.

 

Among the classes of antibiotics, they found that penicillin was “strongly associated with increased colon cancer risk”. Meanwhile, tetracyclines showed a reduced risk of rectal cancer.

 

The links between antibiotics and cancer risk appeared long-lived, as the authors explain:

“The association between antibiotic exposure and colon cancer was seen in participants with antibiotic exposure more than 10 years before [bowel] detection.”

 

This study was the largest of its type. Despite the findings of the current study, there are, however, limitations to it. Although the scientists tried to account for a lot of factors, they were unable to eliminate every possibility.

 

However, the authors conclude:

“Whether antibiotic exposure is causal or contributory to colon cancer risk, our results highlight the importance of judicious antibiotic use by clinicians.”