Antibiotic use is clearly linked to an increased chance of developing colon cancer during the following five to ten years. This was proven following a study on 40,000 cancer cases. The influence of antibiotics on the gut flora is assumed to be the cause of the increased cancer risk.
Author: Sara Majernikova
Artist: Sylvia Cai
Editor: Miranda Hitchens
According to a recent study of over 40,000 cancer cases in Sweden, using antibiotics may increase the chance of acquiring colon cancer five to ten years later. This builds upon previous research (Cao et al. and Dik et al.), which suggested antibiotics may alter the gut microbiome – the population of bacteria that dwell in the digestive system and that these changes may be connected to an increased risk of colon cancer. Researchers indicate in the broadest epidemiological study yet conducted on this relationship that the increased risk may be unique to malignancies of the so-called proximal colon, which links to the small intestine and begins in the lower-right abdomen. When looking at the data, it is highly localised to the proximal, right-sided colon. In fact, the risk of antibiotic-related cancer was highest in the beginning of the proximal colon, or ‘ascending colon’, stretching from the lower- to upper-right abdomen.
According to Lu et al., those who used antibiotics for more than six months had the greatest cancer risk when compared to patients who had not used antibiotics, these participants had a 17% greater risk of developing cancer in the ascending colon. However, the researchers discovered that even short courses of antibiotics carried a cancer risk, although a far lower risk than a months-long regimen. This research may give even another incentive to limit antibiotic overuse- in addition to the creation of antibiotic-resistant superbugs. These new findings support the findings of a similar, but smaller, 2019 UK-based study (Zhang et al.), which really boosts confidence that there’s a significant relationship.
Importantly, these studies only show a link; they do not prove that antibiotics cause subsequent colon cancer. However, there are suggestions about how the medications may make the proximal intestine more susceptible to cancer formation. The idea is that scientists disturb the equilibrium of the microbiota, which may enable infectious bacteria like E.coli and Klebsiella pneumoniae to gain prominence when other microorganisms would normally outcompete them. This, in turn, may increase inflammation in the colon, resulting in the production of reactive chemicals that may damage DNA and cause cancers. Furthermore, the inner lining of the gut may become more porous, enabling bacteria to invade the colon walls and form slimy formations called biofilms. Studies indicate that virtually all proximal colon malignancies, about 90%, are related to such biofilms.
The proximal colon may be more prone to these complications because it receives most antibiotic medication overflow from the small intestine. The medications’ molecules then gradually degrade as they pass through the colon. These putative processes need to be investigated further, but for the time being, the current research reinforces the evidence that there is a relationship between antibiotics and colon cancer. The new research identified tens of thousands of colorectal cancer patients diagnosed between 2010 and 2016 using data from the Swedish Colorectal Cancer Registry. The researchers used data from the Swedish Prescribed Drug Register to follow these individuals’ antibiotic usage from 2005 to 2016, looking for trends. They also compared the cancer patients to almost 200,000 cancer-free adults in Sweden’s general population. While the researchers discovered a definite association between antibiotic usage and cancer in the ascending colon, they found no such link in the distal colon or rectum.
The researchers sought to figure out why the medications were causing cancer in the proximal colon. To do so, they looked into Methenamine Hippurate, a medication that helps prevent urinary tract infections in those who get them regularly. Although it possesses antibacterial properties, the medicine has no impact on the gut flora since it can only be triggered by the high urine acidity. So, according to the notion that antibiotics increase the risk of cancer by interfering with gut bacteria, Methenamine Hippurate should not be associated with the same elevated risk. After further digging through their data, scientists discovered that only antibiotics that influence gut bacteria, not Methenamine Hippurate, showed a relationship to colon cancer. These findings confirm the antibiotic-cancer relationship, although the research has drawbacks. For example, the databases lacked information on people’ diets, smoking habits, or alcohol use, all of which might increase the risk of colon cancer. Similarly, authors were unable to distinguish whether individuals were taking antibiotics for an underlying ailment (e.g., inflammatory bowel disease, associated with colon cancer). Furthermore, although the Swedish Prescribed Medicine Register offers information on drug prescriptions, it cannot reflect whether persons completed their whole course of antibiotics. However, since the research is so extensive, researchers believe it “certainly indicates in the correct way”.
When additional data is obtained, the team plans to do larger-scale follow-up research in a few years to examine whether certain colon cancer subtypes show a greater connection with antibiotics. Cancers may be classified into subtypes depending on the behaviour of their tumour cells and the genetic alterations they contain, and these tiny changes determine where the cancer develops and how it reacts to therapies. Meanwhile, scientists gather data on the microbiomes of people with early-stage colon cancer in order to identify certain gut microbes that are especially deficient or excessive.
While continuing to investigate whether microorganisms have a role in colon cancer, physicians are advised to be cautious about when and how they give antibiotics. In principle, nutritional supplements may be devised to help bring the microbiome back into balance for patients who must take antibiotics – one such supplement was recently tested in malnourished toddlers and helped them establish a varied array of intestinal bacteria. Although, for the time being, the best course of action is to avoid taking antibiotics when not necessary.
Essentially, there is no need to be concerned merely because you have taken antibiotics. The increase in risk is minor, and the impact on the individual’s absolute risk is minimal. Sweden is likewise in the midst of instituting standard colorectal cancer screening. It is crucial to participate in this screening programme, as with any other, so that any cancer may be diagnosed early or perhaps avoided, since cancer precursors can sometimes be eliminated.
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