January 8, 2022

Antibiotics May Increase Colon Cancer Risk, Study Finds

It is almost impossible to imagine the modern world without antibiotics. Several diseases such as the plague, which once killed millions of people, are now treatable with these drugs. However, their overprescribing raises concerns. During the COVID-19 pandemic, antibiotics such as azithromycin were over-prescribed. In addition, flexible regulations facilitate availability, which allows for self-medication. Now, a new study has found that consuming antibiotics increases the chances of developing colon cancer.

According to researchers at Umeå University in Sweden, people who took antibiotics for more than six months had a 17% higher risk of developing proximal colon cancer than those who did not. However, no increase in the risk of distal colon cancer was found, nor in the risk of rectal cancer in humans. Indeed, a slight decrease in the latter was noted in women. The authors suggested that the effect of antibiotics on the gut microbiota could be the reason for this increase.

“The results underscore the fact that there are many reasons to be restrictive with antibiotics. While in many cases antibiotic therapy is necessary and saves lives, in less serious conditions that can be expected to heal anyway, caution should be exercised. all this to prevent bacteria from developing resistance but, as this study shows, also because antibiotics can increase the risk of future colon cancer, ”said study author Dr Sophia Harlid, in a comment. communicated.

A global concern

Large intestine (representative image)Wikimedia Commons

Colorectal cancer (CRC) is the third most common cancer in the world. According to the World Health Organization (WHO), more than 1.9 million new cases of CRC and 935,000 deaths from CRC were reported in 2020. CRC begins either in the colon (the longest part of the fat). intestine) or in the rectum (lower part of the lower part of the large intestine where stool is stored before expulsion).

Age and lifestyle (especially diet, smoking, alcohol consumption, and lack of exercise, among others) are considered to be the most common factors of CRC. However, conditions such as diabetes, obesity, and hereditary syndromes that increase the risk of colon cancer, are among other factors that can increase an individual’s risk of developing CRC.

The large intestine can be roughly divided into three main sections. The proximal colon is the first section that includes the beginning and the middle of the colon. It includes the cecum, ascending colon, hepatic angle, transverse colon and splenic angle). The second section known as the distal colon is the last section of the colon and is made up of the descending colon and the sigmoid colon. The rectum forms this lowest section.

Link cancer and antibiotic use


Tablets (representative image)Pixabay

For the study, the authors used data from 40,545 patients (male = 21,458, female = 19,087) from the Swedish Colorectal Cancer Registry who were diagnosed with CRC between January 1, 2010 and December 31, 2016. Depending on the nature of the cancer, the cases were classified as proximal colon cancer, distal colon cancer, or rectal cancer. Based on the stage of CRC, cases were classified as early stage (stage I-II) and late stage (stage III-IV).

Data from a matched control group of 202,720 cancer-free individuals (males = 107,285, females = 95,435) were selected from the general Swedish population and compared with those from patients with CRC. Sampling was carried out in a manner (incidence density sampling) that ensured a reduction in bias while using cases and controls with different follow-up periods. Information on the use of antibiotics by individuals was obtained from the Swedish Prescription Drug Register for the period 2005-2016.

Higher usage, higher risk


Stomach pain (representative image)Pxfuel

Through their analysis, the team learned that 18.7 percent of all CRC cases and 22.4 percent of controls had not received any antibiotics during the study period. 20.8 percent of CRC cases and 19.3 percent of controls had consumed antibiotics for more than 2 months. Of the CRC patients, 36.5% had been diagnosed with proximal colon cancer, 29.3% had distal colon cancer, and 33% had rectal cancer. The median duration of follow-up was 8 years and the mean age of diagnosis of CRC was 72 years.

Scientists noted that there was a visible risk of colon cancer five to ten years after taking the antibiotics itself. As expected, the increased risk was highest among those who took the most antibiotics. The increased risk of proximal colon cancer was 9% for moderate use (10 days to 2 months) of antibiotics, while it was 17% for very high use (over six months). However, the greatest increase in cancer risk was in the ascending colon (14%).

Interestingly, the study found no increased risk of cancer in the descending colon due to the use of antibiotics. However, an opposite association or decreased risk of rectal cancer has been observed, especially in women (around 9%).

Potential role of the gut microbiome

Stomach pain

Abdominal pain (representative image)Flick / Marco Verch

With a strong link established between antibiotic use and an elevated risk of cancer, the authors sought to understand how antibiotics risk these. Therefore, they investigated a non-antibiotic bactericidal drug, methenamine hippurate, prescribed for the treatment of UTIs. These drugs have no impact on the microbiome. They gleaned that there was no difference in the incidence of colon cancer among those who used the drug. This, according to the authors, indicated that it is the effect of antibiotics on the microbiome that worsens the risk of cancer.

Although the present study only analyzed antibiotics given by mouth, it is likely that intravenous antibiotics may also have an impact on the gut microbiota present in the intestinal system. Despite these results, it is not possible to overlook the role of antibiotics in treating disease. “There is absolutely no reason to be alarmed just because you have taken antibiotics. The increase in risk is moderate and the effect on the absolute risk for the individual is quite small, ”assured Dr. Harlid.

Stressing the importance of regular screening for CRC, Dr Harlid informed that Sweden, where the study was being conducted, is in the process of introducing routine screening for the disease. “Like any other screening program, it is important to participate in it so that any cancer can be detected early or even prevented, because the precursors of cancer can sometimes be eliminated,” she concluded.

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