Large Kaiser Permanente study suggests adult use of antibiotics not tied to increase in colorectal cancer diagnoses in adults under 50
Antibiotics used in adulthood are unlikely to be a reason for the increase in colorectal cancer diagnoses seen in adults under age 50, a new Kaiser Permanente study suggests.
Since the 1990s, there has been a notable increase in colorectal cancer in people under 50. To identify these cancers as early as possible, the U.S. Preventive Services Task Force updated its guidelines in 2021 to recommend that screening for colorectal cancer begin at age 45 — instead of 50. Researchers also began looking for reasons why rates in younger people were rising.
The new study, published in Clinical Gastroenterology and Hepatology, focused on whether antibiotic use might be a contributing factor.
“It’s been hypothesized that antibiotics might disrupt the microbiome in a way that promotes colorectal cancer,” said senior author Jeffrey K. Lee, MD, MPH, a research scientist with the Kaiser Permanente Division of Research and a gastroenterologist with The Permanente Medical Group (TPMG). “Ours is the first study done in the United States to focus on antibiotic use in adults under age 50, and we found no evidence that antibiotic use in adulthood increases colorectal cancer risk in this population.”
The study included 1,359 Kaiser Permanente Northern California (KPNC) members who were diagnosed with colorectal cancer between the ages of 18 to 49. Each patient was matched with 4 healthy KPNC members who were the same age, sex, and race or ethnicity. The researchers compared oral antibiotic use between the 4,711 healthy patients and the 1,359 patients with colorectal cancer.
The study found no association between the number of times a person was prescribed antibiotics and risk of being diagnosed with colorectal cancer. These analyses considered both the type of antibiotic that was prescribed and where in the colon or rectum the cancer developed. The study also accounted for factors such as body mass index, smoking history, diagnoses of diabetes, diverticulitis, or other diseases, family history of colorectal cancer, and previous medical visits or hospitalizations.
Ours is the first study done in the United States to focus on antibiotic use in adults under age 50, and we found no evidence that antibiotic use in adulthood increases colorectal cancer risk in this population.
— Jeffrey K. Lee, MD, MPH
Lee said the findings add to the evidence that suggests adult antibiotic use is not tied to increased colorectal cancer risk. “Many studies have looked at colorectal cancer and antibiotic use in people 50 and over,” said Lee. “Some of these studies showed a weak link and others showed no link. Only 3 other studies — conducted outside of the U.S. — have looked at adult antibiotic use and colorectal cancer in adults under 50 and these studies, like ours, found no association.”
Lee and his team noted this new study cannot rule out whether antibiotic use in childhood or adolescence or exposure during pregnancy may contribute to the increase in colorectal cancer in adults under 50. “It’s possible there may be certain times early in our lives when antibiotic use affects the gut microbiome in a way that sets the stage for colorectal cancer to develop,” Lee said, noting that more research is needed to answer this question.
“Antibiotics play an important role in medical care, and they are necessary for treating illnesses and diseases caused by bacteria, like strep throat and pneumonia,” said Lee. “I wouldn’t want a person who needs antibiotics to not take them because they are worried it will increase their risk of colorectal cancer.”
At the same time, he said, “We know that antibiotic resistance is a real concern because all too often people take antibiotics for things they can’t treat, like a cold, the flu, or bronchitis. We need to continue to have doctors prescribe them only when necessary.”
The study was funded by the National Cancer Institute and Kaiser Permanente Northern California Graduate Medical Education.
Co-authors include Kevin J. Kane, MD, Pradeep Koripella, MD, Xiaoran Li, MD, and Jeffrey M. Hendel, MD, of The Permanente Medical Group; and Christopher D. Jensen, PhD, MPH, Jingrong Yang, MA, Huyun Dong, MPH, Sophie A. Merchant, MPH, and Douglas A. Corley, MD, PhD, of the Division of Research.
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About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 450 epidemiological and health services research projects. For more information, visit divisionofresearch.kaiserpermanente.org or follow us @KPDOR.
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