People who take antibiotics are at an increased risk of developing colon cancer within five to ten years. The research was published in the Journal of the National Cancer Institute by researchers at Umeå University in Sweden.
Cases of colon cancer have fallen since the mid-1980's thanks to more people getting screened and changing lifestyle-related risk factors. However, while cases have decreased among older adults, cases have been rising in younger adults since the mid-1990s. Between 2012 and 2016, the incidence of the disease increased by 2% per year among people younger than 50.
Earlier studies have found a link between antibiotic use and colon cancer. Researchers have suspected this to happen as while antibiotics eradicate bacterial infections, they also kill off beneficial bacteria, and may allow pathogenic ones to thrive.
In the present study, researchers compared antibiotic use between 2005 and 2016 between 40, 545 people with colon cancer and 202, 720 healthy controls. In doing so, they found that men and women who took antibiotics for over six months had a 17% greater risk of developing colon cancer in the ascending colon- the first part of the colon reached by food after the small intestine- than those not prescribed antibiotics. This increased risk was visible within five to ten years of taking antibiotics.
The researchers note, however, that the risk did not exist for cancer in the descending colon. Meanwhile, while women taking antibiotics were slightly more likely to develop rectal cancer, the same risk was not observed in men.
The researchers also studied the effects of a non-antibiotic bactericidal drug used against urinary infections that do not affect the microbiome. They found that this drug was not associated with an increased risk of colon cancer, suggesting to the researchers that the reason antibiotics are linked to higher rates of cancer may be due to their effects on the microbiome.
"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," said Sophia Harlid, one of the authors of the study.