Antibiotics may increase risk of bowel cancer, long-term behavioural changes

According to a recent study published in the journal Gut, long-term use of antibiotics during adulthood increases the likelihood of developing precursors to bowel cancer. The research, once again, underlines the vital role of gut bacteria.

Risk factors include a lack of physical activity, a low intake of fruits and vegetables, being overweight or obese, and alcohol consumption. A new study, published this week, may add long-term antibiotic usage to this list.

Links between antibiotics and a range of conditions have come to light over recent years, including irritable bowel disease, celiac disease, and even obesity. This connection between antibiotics and disease is thought to be due to the effect of antibiotics on the makeup of gut bacteria (the microbiome); by altering the numbers and types of bacteria present in the gut, metabolic or pathological processes may be triggered.

Some studies have also hinted that antibiotic usage could be linked with bowel cancer, but previous studies have only consisted of relatively short monitoring periods. As the authors conclude: “The findings, if confirmed by other studies, suggest the potential need to limit the use of antibiotics and sources of inflammation that may drive tumor formation.”

Also, in a landmark study, researchers at St. Joseph’s Healthcare Hamilton and McMaster University have found that providing clinical (low) doses of penicillin to pregnant mice and their offspring results in long-term behavioural changes.

These changes include elevated levels of aggression and lower levels of anxiety, accompanied by characteristic neurochemical changes in the brain and an imbalance in their gut microbes. Giving these mice a lactobacillus strain of bacteria helped to prevent these effects.

The study was published in Nature Communications and was funded by the United States Office of Naval Research. Other studies have shown that large doses of broad-spectrum antibiotics in adult animals can affect behaviour. But there haven’t been previous studies that have tested the effects of clinical doses of a commonly-used, narrow-spectrum antibiotic such as penicillin on gut bacteria and behaviour.

A previous study in 2014 raised similar concerns after finding that giving clinical doses of penicillin to mice in late pregnancy and early life led to a state of vulnerability to dietary induction of obesity.

The research team will follow up their studies by analyzing the effects of penicillin on the offspring, if given only to the pregnant mothers. They also plan on investigating the efficacy of different types of potentially-beneficial bacteria in protecting offspring against the behavioural changes that result from antibiotic usage.