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Long-Term Antibiotic Use Impacts Gut Microbiome, Linked With Cognitive Decline In Older Adults

Intestinal micro-organisms mediate the gut-brain axis and research has shown they may also contribute to, anxiety, schizophrenia, and other psychiatric depression conditions. This means the gut and brain communicate with each other via direct neural connections, hormones, or metabolic products. In a new study published in PLOS One, researchers found that long-term antibiotic use in midlife might be associated with cognitive decline in later life due to gut microbiome changes.

Previous studies have associated chronic antibiotic use with an increased risk of conditions related to chronic inflammation, including obesity, cancer, and cardiovascular disease. Despite the fact that some gut bacterial species recover after the completion of antibiotic treatment, there are still shifts in the overall gut microbial community and changes to certain bacterial genes persist months to years after drug exposure.

But the evidence linking antibiotic use with cognition is limited. The micro-organisms that dwell in the gastrointestinal tract are known to induce cognitive side effects.

To delve deeper, the study’s researchers included 14,542 US-based nurses as participants from the Nurses Health Study II database which is an ongoing nationwide cohort study that began in 1989 and investigates the risk factors for major chronic diseases in women. The participants’ mean age was 61 years old. The participants reported using antibiotics for at least two months at a stretch. The most common reasons for being prescribed antibiotics were respiratory infection, urinary tract infection (UTI), acne/rosacea, chronic bronchitis, and dental treatments.

They had completed a self-administered psychological test between 2014–2018 using a computer at home. The test comprised four tasks including measuring their psychomotor functions and information processing speed. This involved pressing a particular key when a playing card on the screen flips over. The second task included measuring the women’s vigilance and visual attention, in which they press a key when a red card flips over.

For measuring their visual learning and short-term memory, the researchers designed the test where participants were shown playing cards and then asked to remember if they have seen the card previously. The researchers then recorded their scores and generated standardized averages based on these various parameters.

“We observed that antibiotic use in midlife was significantly associated with subsequent poorer scores for global cognition, learning, and working memory, and psychomotor speed and attention on a cognitive assessment administered a mean of 7 years later,” the researchers wrote. Given the profound effect of antibiotic use on the gut microbiome —the gut-brain axis could be a possible mechanism for linking antibiotics to cognitive function.”

In a 2016 study published in the American Academy of Neurology, researchers observed that antibiotics may be linked to a severe disruption in brain function called delirium. This state of mental confusion could also result in hallucinations and agitation.

But the researchers of the new PLOS One study noted that their findings had limitations. Their antibiotic data did not contain information about the specific antibiotic types. Also, the antibiotic use of the participants was based on self-report several years after use and could be subject to misclassification.

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