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New research suggests overuse of antibiotics may raise risk of colorectal cancer. Jamie Grill Atlas/Stocksy
  • The use of antibiotics has increased dramatically in recent years.
  • New research indicates that increased use of antibiotics is linked to a greater risk of colon cancer, particularly in people under the age of 50 years.
  • The new data reinforce the need to reduce the unnecessary use of antibiotics, which can put individuals at further risk of health problems.

Antibiotics are extremely helpful in the treatment of infection. However, scientists are still learning about health problems that result from antibiotic use and overuse.

Results of a new study, which were shared at the European Society for Medical Oncology World Congress on Gastrointestinal Cancer 2021, indicate that people, especially those under the age of 50 years, may be at an increased risk of colon cancer due to the use of antibiotics.

This new information reinforces the importance of careful prescription of antibiotics and potentially adds weight to arguments for colon cancer screening among younger people.

The Centers for Disease Control and Prevention (CDC) note that antibiotics are useful in the treatment of certain types of infection. While doctors use them to treat bacterial infections, they are not effective against infections caused by viruses.

Moreover, antibiotics are not always necessary, because sometimes, the body is able to ward off the infection on its own.

Unnecessary use of antibiotics is a growing concern nationally and internationally. In the United States, the CDC is advocating for the careful use of antibiotics to avoid adverse effects.

For example, people taking antibiotics are at risk of Clostridioides difficile infections and other infection types that are resistant to antibiotics.

Moreover, the National Institutes of Health (NIH) note that antibiotics can kill off the helpful bacteria in the gastrointestinal tract.

In order to balance these risks, healthcare professionals need to avoid prescribing antibiotics that are not a necessary treatment. Unneeded antibiotic prescriptions make up at least 30% of outpatient antibiotic prescription in the U.S.

Dr. Michael Woodworth, assistant professor of infectious diseases at Emory University School of Medicine in Atlanta, GA, told Medical News Today:

“A major challenge in improving healthcare provider antibiotic use is a skewed understanding of the balance of potential benefits over poorly characterized risks. Improving stewardship of our available antibiotics is an important global priority in both reducing potential toxicities of antibiotics and selective pressures for greater resistance to antibiotics.”

Current information favors careful use of antibiotics, and researchers are still studying further risks associated with their use.

The American Cancer Society notes that, if skin cancers are excluded, colorectal cancer is the third most common type of cancer diagnosed in the U.S.

Overall, the incidence of colorectal cancer has decreased in recent years. However, the number of colorectal cancer cases among individuals under the age of 64 years has grown.

There is a mounting concern about the prevalence of colorectal cancer in younger individuals.

Recent data published in the journal Cancer suggest people should undergo screening for colorectal cancer at the age of 45 instead of 50 to help aid in early detection and prevention.

Emphasis on prevention and detection has to do with the health impact of and mortality rates due to colorectal cancer, which is the second leading cause of cancer-related deaths in the U.S.

Individuals can reduce their likelihood of developing this type of cancer by avoiding certain risk factors, such as alcohol consumption, tobacco use, and lack of physical activity.

However, experts also associate colorectal cancer with non-modifiable risk factors, such as age, family history, genetics, or the presence of inflammatory bowel disease (IBD). These are some of the reasons early screening is crucial for reducing colorectal cancer mortality.

Some predisposing factors for colorectal cancer remain unknown or are still being studied, such as this new association between antibiotic use and colon cancer. As researchers investigate new risk factors for colorectal cancer, screening will likely become even more critical.

Authors of the present study, which is a nested case-control study, gathered data from patients in Scotland and analyzed cases of early onset and later onset colorectal cancer.

They classified individuals under the age of 50 years as having early onset colorectal cancer, and those aged 50 years or older as having later onset colorectal cancer.

The researchers compared a total of 7,903 individuals with colorectal cancer with 30,418 individuals in the control groups. Of the study participants with a colorectal cancer diagnosis, 445 were under the age of 50.

The researchers examined the prescription of oral antibiotics and antibiotic exposure period in those with colorectal cancer and in the matched control groups.

They found a link between antibiotic use and an increased risk of colon cancer in both the early and later onset categories.

Risk of colon cancer related to antibiotic use varied between the early onset and later onset groups.

According to the study results the researchers shared, people with later onset colorectal cancer had an associated risk of 9%. The association was much higher in those with early onset colorectal cancer, with an almost 50% increased risk.

However, this risk was not associated with every type of antibiotic or every type of colorectal cancer. The researchers note that “[a]mong both age groups, most classes of antibiotic were not significantly associated with colon, rectal, or distal colon cancer.”

In the younger age group, the increased risk was related to cancer found in the first part of the large intestine and the use of quinolones and sulfonamides/trimethoprim antibiotics.

Dr. Woodworth pointed out that there could be several reasons for this and that further research will be necessary:

“It may be that the antibiotics were prescribed for symptoms from a tumor that were misattributed to an infection, that comorbid conditions, such as IBD, could have increased likelihood of getting antibiotics and tumors, or, as the authors suggest, a more direct negative effect of antimicrobials on bacterial communities that may have otherwise helped protect from development of cancer.”

“More focused research would be needed to better understand if antibiotics played a role in causing cancer or were just associated in this study,” he added.

The study raises awareness of potential risk factors for colon cancer and promotes caution in the use of antibiotics. The study further emphasizes that younger individuals are still at risk of colon cancer.

While more research is necessary in this area, and cause cannot be proven based on the nature of the study, the authors conclude:

“Our findings suggest antibiotics may have a role in colon tumor formation across all age groups, particularly in those aged less than 50 years. It is possible that exposure to antibiotics could be contributing to the observed increases in [early onset colorectal cancer], particularly in the proximal colon.”

“If confirmed, our study will provide further reasons to reduce, where possible, frequent and unnecessary antibiotic prescribing.”