Antibiotics and cognitive decline: is there a link?

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Does antibiotic use influence cognitive decline? Guido Mieth/Getty Images
  • A recent study found that chronic antibiotic use in midlife in women was linked to a mild decline in cognitive abilities 7 years later.
  • Small decreases were observed in psychomotor speed, attention, working memory and learning.
  • Future research is needed to confirm this association and determine if changes in cognitive function can be reversed.

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

The intestinal microbiota is essential to regulate our internal environment and the functioning of the immune system.

There is a two-way communication between the central nervous system and the gut, 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 lives. There is some evidence that changes in the gut microbiome may play a role in the development of psychiatric and neurological disorders, such as depression, autism spectrum disorder, schizophrenia, anxietyand Alzheimer’s disease.

The use of antibiotics can alter the microbial communities of the intestine because, by their very nature, they kill bacteria. These changes can last for months or years after exposure.

Few studies have examined the later 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 at 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 nurses with an average age of 54.7 years.

The questionnaire contained information on the duration of use of antibiotics in the past 4 years and the reason for their use.

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

The CogState tests measured participants’ performance in the following tasks:

  • Detection: Press a key when a playing card turns up.
  • Identification: Press a key when a red card rolls over.
  • A learning map: The participant is shown playing cards and asked to remember if they have seen the card before.
  • A back : The participant is asked if a playing card on the screen is the same as the one shown previously.

The average combined detection and identification score measures attention and psychomotor speed — the speed with which participants recognized and reacted to environmental changes. Learning a card and returning mean composite score metrics working memory and learning.

Combining the scores for the four tasks produced an “overall cognition score.”

Researchers categorized participants by antibiotic use: no use, less than 15 days, 15 days to 2 months, and more than 2 months. They adjusted cognitive test scores based on the participants’ age and the education level of their spouses and parents.

After 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 exposure to antibiotics..

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

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

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

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

“The continued use of antibiotics is harmful in many ways to our health. […] This study showed 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, head of the clinical and translational epidemiology unit at Massachusetts General Hospital and co-lead author spoke with DTM on the strengths of the study.

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

Dr. Ross noted that although the study had a large number of participants, many variables can affect cognition. Considering all variables in an analysis is not possible.

“We cannot exclude the possibility that another risk factor associated with mid-life antibiotic use is the cause of the mild decline in cognitive function.“, Dr. Chan agreed.

Dr. Ross stressed the importance of “taking antibiotics as prescribed […] and be proactive. You can always ask your medical team too [if] something is wrong or you are on antibiotics for more than 7 days.

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

– Dr. Chan

Dr Ross added: “We are discovering the power of probiotics and how they have a […] significant impact on our health. It is important to have a healthy diet, exercise regularly, get enough sleep and keep alcohol consumption to a minimum, especially in treatment.

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