A person paints on a canvas in an art studio. Share on Pinterest
Long-term antibiotics use in midlife may lead to cognitive decline in women later in life, according to new research published in the journal PLOS ONE. Javier Pardina/Stocksy United
  • Women who use a lot of antibiotics in midlife may be more likely to have cognitive decline later, according to new research.
  • There may be a link between the gut microbiome and cognitive decline.
  • Experts caution that decisions about antibiotics should be made in consultation with a health professional.
  • Doctors already know several key modifiable risk factors for cognitive decline.

Women who use a significant amount of antibiotics in midlife are more likely to have a cognitive decline in later life, according to new research published in the journal PLOS One.

The study involved 14,542 female nurses in the U.S.

Assessment on cognitive functioning came from a self-administered computerized neuropsychological test battery between 2014 and 2018.

Compared with non-antibiotic users, women who reported taking antibiotics for at least 2 months in midlife (mean age of 54.7) had lower mean cognitive scores 7 years later.

Cognitive scores included global cognition, psychomotor speed and attention, and learning and working memory. The researchers found an association between increasing total exposure to antibiotics in midlife and lower cognitive scores in all three cognitive domains.

According to the researchers, the effect was equivalent to what would be expected for 3 to 4 years of aging.

"These data provide a better understanding of potential complications of antibiotics throughout life, as well as generate hypotheses about the role of the gut microbiome in cognition," study authors wrote.

Previous research suggests that antibiotics can cause significant changes in gut microbiota, which can affect short- and long-term health.

Dr. Jan K. Carney is the associate dean for public health and health policy and a professor of medicine at Larner College of Medicine at the University of Vermont.

Carney told Healthline this was a well-conducted observational study using the Nurses' Health Study II, with more than 100,000 female participants.

"A couple of notable features of these studies is that they have thousands of participants. The return rate for questionnaires obtained every 2 years is over 90 percent, which is extraordinary," Carney said.

"Similar studies could be replicated in other populations, including males, and importantly, in diverse populations, to see whether these findings are noted beyond the group studied," said Carney.

"Readers shouldn't interpret this important study as personal advice about antibiotic use or duration," Carney said.

The researchers broke down antibiotic use as:

  • none
  • 1 to 14 days
  • 15 days to 2 months
  • 2 months or more

Carney explained that these categories were used to show differences in measures of cognitive decline as compared to no antibiotic use and to see if the trend increased with longer antibiotic duration.

The study did not include information on specific antibiotics or routes of administration. And because the information was self-reported several years after antibiotic use, the data is subject to recall errors.

"The women who used antibiotics were also more likely to have chronic conditions and generally may have been in poorer health, which might be related to cognition as well," said Carney.

The most common reasons given for chronic antibiotic use were:

  • respiratory infections
  • other (including acne)
  • urinary tract infections
  • dental problems

"Someof the infections mentioned in the study can be quite serious if untreated," said Carney.

On a population level, though, it reinforces what public health experts say about using antibiotics only when necessary, she added.

"As an example, the U.S. Centers for Disease Control and Prevention highlights the appropriate use of antibiotics for some bacterial infections and reminds us that they are not effective for treating viruses, such as the common cold. Overuse of antibiotics can result in antibiotic resistance," said Carney.

Carney advises individual health decisions, including when and how long to take an antibiotic, are best made in consultation with a health professional.

Dr. Scott Kaiser is a board certified geriatrician and director of geriatric cognitive health for the Pacific Neuroscience Institute at Providence Saint John's Health Center in Santa Monica, California.

Kaiser told Healthline there's a desperate need to help reduce the risk of developing dementia in the first place.

"We're on course to have over 150 million people worldwide with dementia in the coming decades. We need to think collectively, holistically, over the life course as to how to bend that curve and reduce the future burden of dementia." Kaiser said.

Kaiser noted that of all the factors that may contribute to cognitive decline, this isn't one we typically think of. "But in fact, there's some evidence linking the health of the gut microbiome and cognitive health."

"The researchers did a really good job accounting for many potential variables and controlling for them to assure the association between antibiotics and cognitive decline was real and robust," said Kaiser.

"But this study, like similar studies, is really a hypothesis," Kaiser continued. "It raises interesting questions that should be studied further. And if antibiotics do impact the gut microbiome, are there things to mitigate that, such as probiotics or a certain diet?"

Kaiser doesn't want people to think they shouldn't take antibiotics.

"There's a risk-benefit calculation. Antibiotic stewardship is the idea that antibiotics should be prescribed judiciously, meaning there's a clear need and clear potential benefit and potential risks have been considered," Kaiser explained.

Gut microbiome health should be added to the overall checklist of maintaining a healthy brain, said Kaiser, adding that there's a long list of things we know can promote brain health.

"Regular exercise is probably the closest thing we have to a miracle drug when it comes to brain health. And a diet rich in nutrients and antioxidant-rich fruits and vegetables as a mainstay, and low in processed foods," said Kaiser. "Smoking and excessive alcohol consumption are also modifiable risk factors for dementia."

Kaiser stressed the critical need for good primary care and managing blood pressure, cholesterol, and blood sugar.

"Some of these seem obvious, some others not so much. Loneliness and social isolation can contribute to cognitive decline. Having healthy, meaningful relationships is a core aspect of overall health and well-being," said Kaiser.

Kaiser said that broader public health issues also play a role.

"Culture change is needed to prioritize good, healthy sleep and healthy ways to cope with stress and anxiety," Kaiser said.

"This study doesn't demonstrate that antibiotics cause dementia. But it's an interesting study that can advance efforts in the field in a deeper way. It's an opportunity to think about how gut health affects brain health and to be thoughtful about antibiotics," said Kaiser.