A recent study published in the Journal of the National Cancer Institute demonstrates a clear association between antibiotic use and an increased risk of developing colon cancer. The influence of antibiotics on the intestinal microbiome is assumed to be the cause of the increased cancer risk.
Researchers discovered that women and men who took antibiotics for more than six months had a 17% higher chance of getting cancer in the ascending colon, the first region of the colon to be touched by food following the small intestine, than those who did not.
However, no higher risk of cancer in the descending colon was discovered. Men taking antibiotics showed no increased risk of rectal cancer, but women taking antibiotics had a slightly lower incidence of rectal cancer.
Colon cancer risk was already enhanced five to ten years following antibiotic use. While the increase in risk was greatest for those taking the majority of antibiotics, an admittedly tiny but statistically significant increase in risk of cancer was also observed following a single course of antibiotics.
The current study analyzes data from the Swedish Colorectal Cancer Registry for 40,000 individuals between 2010 and 2016. These were compared to a matched control group of 200,000 cancer-free people randomly selected from the general Swedish population.
Data on the individuals’ antibiotic use was collected from the Swedish Prescribed Drug Register for the period 2005-2016. The Swedish study broadly confirms the results of an earlier, somewhat smaller British study.
To better understand how antibiotics increase the risk, the researchers also looked at a non-antibiotic bactericidal medication used to treat urinary infections that do not change the microbiome.
There was no difference in the frequency of colon cancer among individuals who used this medicine, implying that the influence of antibiotics on the microbiome raises the risk of cancer. While the study only looked at orally delivered antibiotics, intravenous medicines may also have an effect on the gut microbiota.
“There is absolutely no cause for alarm simply because you have taken antibiotics. The increase in risk is moderate and the affect on the absolute risk to the individual is fairly small. Sweden is also in the process of introducing routine screening for colorectal cancer. Like any other screening programme, it is important to take part so that any cancer can be detected early or even prevented, as cancer precursors can sometimes be removed,” says Sophia Harlid.
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