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Does antibiotic use influence cognitive decline? Guido Mieth/Getty Images
  • A recent study found chronic midlife antibiotic use in women was linked to mild decreases in cognitive ability 7 years later.
  • Small decreases were seen in psychomotor speed, attention, working memory, and learning.
  • Future research is neccessary to confirm this association and investigate whether the changes in cognitive function can be reversed.

The gut microbiome consists of all the microbes and their genetic material living in our gastrointestinal tract. These microbes include bacteria, fungi, and viruses.

The gut microbiome is essential for regulating our internal environment and the function of the immune system.

There is two-way communication between the central nervous system and the gut, which is called the gut-brain axis. Scientists believe that the gut-brain axis allows our gut bacteria to influence the brain.

The gut microbiome modulates brain development and function throughout our life. There is some evidence that changes to the intestinal microbiome may play a role in developing psychiatric and neurologic conditions, such as depression, autism spectrum disorder, schizophrenia, anxiety, and Alzheimer’s disease.

Antibiotic use can alter microbial gut communities as, by their very nature, they kill bacteria. These changes can last for months or years after exposure.

Few studies have examined the subsequent cognitive effects of chronic antibiotic use in midlife in participants without dementia.

Researchers from Massachusetts General Hospital and Harvard Medical School, both in Boston and Rush University Medical Center in Chicago set out to investigate. They examined the effect of chronic antibiotic use in midlife on cognitive function.

Their findings appear in PLOS ONE.

The study analyzed the 2009 Nurses’ Health Study II questionnaire, which includes data from 15,129 female nurses with an average age of 54.7.

The questionnaire contained information about the duration of antibiotic use over the past 4 years and the reason for their use.

Participants completed a validated, computerized cognitive assessment for dementia called CogState. They completed this at home an average of 7 years after their first antibiotic exposure.

CogState testing measured participants’ performance in the following tasks:

  • Detection: Pressing a key when a playing card turns over.
  • Identification: Pressing a key when a red card flips over.
  • One card learning: The participant is shown playing cards and asked to recall if they saw the card previously.
  • One back: The participant is asked if a playing card on the screen is the same as one shown previously.

The combined average score of detection and identification measures attention and psychomotor speed — how rapidly participants recognized and responded to environmental changes. The one card learning and one back mean composite score measures working memory and learning.

Combining scores for all four tasks produced a “global cognition score.”

The researchers classified participants by antibiotic use: no use, less than 15 days, 15 days to 2 months, and over 2 months. They adjusted the cognitive testing scores for the participants’ age and the education level of their spouse and parent.

After the adjustment, they found small decreases in global cognition (-0.11), psychomotor speed and attention (-0.13), and working memory and learning (-0.10) after more than 2 months of antibiotic exposure.

The cognitive declines measured in these three categories remained similar after adjusting for other risk factors such as chronic diseases.

As we age, cognitive abilities tend to decline. As expected, scientists showed that average Cogstate scores dropped with each year of age.

Using this as a benchmark, the authors conclude that “the relation of antibiotic use to cognition was roughly equivalent to that found for 3 to 4 years of aging.”

Dr. Sherry Ross, MD, a specialist in obstetrics and gynecology at Providence Saint John’s Health Center in Santa Monica, CA spoke with Medical News Today about the study results:

“Ongoing antibiotic use is harmful in many ways to our health. […] This study showed yet another association of how chronic antibiotic use […] may have an association with a decline in cognitive abilities.”

Dr. Andrew T. Chan, MD, MPH, a professor of medicine at Harvard Medical School, chief of the Clinical and Translational Epidemiology Unit at Massachusetts General Hospital, and co-senior author spoke to MNT about the study’s strengths.

He felt that data collection about antibiotic use years before the onset of cognitive decline minimized the risk for inaccurate recall. Dr. Chan explained that they “had detailed cognitive assessments, which allowed us to examine relatively subtle changes in cognition related to mid-life antibiotic use.”

Dr. Ross commented that although the study had a large number of participants, many variables may affect cognition. Accounting for all variables in an analysis is not possible.

“We cannot rule out the possibility that some other risk factor associated with the use of antibiotics in mid-life is the cause of the mild declines in cognitive function,” Dr. Chan agreed.

Dr. Ross expressed the importance of “taking antibiotics as prescribed […] and being proactive. You can always question your medical team as well [if] something doesn’t feel right or if you’re on antibiotics for more than 7 days.”

“Our study […] opens new avenues of research into possible ways of modifying the gut microbiome to prevent cognitive decline with aging. This also underscores the importance of judicious use of antibiotics across the life course to minimize potential long-term consequences of altering the gut microbiome.”

– Dr. Chan

Dr. Ross added, “We’re learning about the power of probiotics and how they have a […] significant impact on our health. Eating a healthy diet, exercising regularly, sleeping adequately, and minimizing alcohol use is important, especially in treatment.”