Study Shows Link between Antibiotic Use in Midlife and Cognitive Impairment

Key Takeaways:

Long-term antibiotic use in midlife may be linked to later-life cognitive decline in women.
This link may stem from disruptions to gut bacteria, which affect brain health through the gut-brain axis.
The results are observational, so they don’t prove cause and effect.
Always use antibiotics only when prescribed, and discuss long-term risks with your doctor if taking them frequently.

A study that appeared recently in the open-access journal PLOS ONE shows that the use of antibiotics in midlife by women could promote cognitive decline years later.

Old Woman With Dementia

The large-scale study was carried out by scientists from Massachusetts General Hospital, Harvard Medical School, and Harvard T.H. Chan School of Public Health. Researchers from Rush Medical College and Boston’s Brigham and Women’s Hospital also took part.

Subjects who used antibiotics for months during a period returned lower scores in neuropsychological tests done several years later. The effects were comparable to those of up to four years of aging. However, the study was observational and cannot confirm that antibiotics directly caused the cognitive decline—it only shows an association.

Antibiotics and cognitive function

One possible explanation for the observed outcomes is that antibiotic use disrupts the gut microbiota, which may impact brain function through the gut-brain axis. It is also possible that the drugs have direct effects on the brain that contribute to cognitive decline.

Studies have revealed a link between gut microbiota and brain health via what is known as the gut-brain axis. This means that the gut communicates with the central nervous system. This communication pathway, known as the gut-brain axis, allows signals to pass between the brain and the digestive system. Gut microbes help produce key neurotransmitters like serotonin and GABA, which influence mood, memory, and attention. They also activate the vagus nerve, a direct signaling pathway to the brain. Disruptions here may affect cognitive functions in subtle but cumulative ways. When the gut’s bacterial balance is disturbed—a condition called dysbiosis—it can trigger inflammation and disrupt mental health. It is not surprising, then, that what affects the gut may impact mental health.

In one study, people with Alzheimer’s were found to have a modified gut microbiome when compared to healthy individuals. They had more of the clinical pathogens Bacteroides while having less of the beneficial Bifidobacterium species, for example.

Previous research also shows that the use of antibiotics can cause major microbiome disruptions, leading to undesirable effects. Chan said the drugs and the resulting disruptions could contribute to a low-grade, chronic inflammatory state—an established risk factor for cognitive decline.

In mice, for example, scientists have shown a link between antibiotic use and gut dysbiosis as well as cognitive impairment. However, these animal studies, while useful for hypothesis generation, don’t directly confirm effects in humans due to species-specific differences. But these drugs were not detected in the brain.

One of the ways gut microorganisms impact mental health is by promoting the release of neurotransmitters. They can help to activate the vagus nerve and are able to interact with immune cells.

Cognitive impairment in women

For this research, scientists made use of data from the Nurses’ Health Study II. This is an ongoing effort that collects female nurses’ health data over several years.

The research team examined the information of more than 15,000 female nurses regarding antibiotic use and their performance in cognitive tests. It divided the nurses into groups based on their antibiotic use, ranging from no use to using for more than two months.

The researchers, who honed in on middle-aged female nurses with a mean age of 54.7 years, compared people who used antibiotics over different lengths of time to people who did not use them. These subjects were assessed on cognitive tests relating to memory, attention, learning, and thinking speed. The tests were conducted seven years after antibiotic use.

Since the assessments were self-reported and done online, they may have been influenced by user bias, familiarity with digital tools, or differing health literacy levels. These factors can affect accuracy compared to clinical testing.

It is important to note that the cognitive assessments were self-reported and completed online, which may introduce variability based on factors like lifestyle, overall health, or digital familiarity.

Female nurses who used antibiotic drugs for at least two months returned lower cognitive scores, compared to those who used them for shorter durations or took none.

The scientists compared the extent of observed cognitive decline to that of three and four years of aging.

However, Chan noted that it was too early to use these findings for recommendations on antibiotic use to protect mental health. It only shows a need for caution when using these drugs for now.

FAQs: Antibiotics and Cognitive Health

Does taking antibiotics in midlife cause cognitive decline?
The study doesn’t prove causation but found a link between longer antibiotic use (2+ months) and lower scores on memory and thinking tests years later.

What kind of cognitive issues are we talking about?
Mainly subtle declines in memory, attention, learning, and thinking speed—comparable to 3–4 years of brain aging.

Why would antibiotics affect the brain?
One theory is that antibiotics disrupt the gut microbiome, which is closely connected to brain health through the gut-brain axis.

What is the gut-brain axis?
It’s the two-way communication between the digestive system and the brain. Disrupting gut bacteria may lead to inflammation and cognitive issues.

Should people stop taking antibiotics?
No, but they should be used only when truly necessary. Overuse can harm both gut health and long-term brain function.

Is this risk the same for men?
This study focused on women, so we can’t say for certain. More research is needed on men.

Can I reverse or reduce the effects?
You can support your gut and brain by eating a fiber-rich diet, taking probiotics, staying mentally active, and exercising regularly.

What can I do if I have used antibiotics in the past?
Focus on restoring gut health with prebiotics, fermented foods like yogurt or kimchi, and reducing processed sugars. Staying mentally active and physically fit also supports brain function over time.

Do probiotics help?
Some evidence suggests certain strains like Lactobacillus rhamnosus and Bifidobacterium longum may support gut-brain health. Speak with a healthcare provider for personalized guidance.

Is short-term antibiotic use safe?
The study found risks mainly in those who used antibiotics for over two months. Occasional, medically necessary use is unlikely to have the same impact.

Should this change how doctors prescribe antibiotics?
It may encourage more cautious prescribing, especially for non-urgent conditions, and support guidelines that limit unnecessary use.

Bottom Line

If you’ve taken antibiotics in midlife, don’t panic—but do take note. While the link to cognitive decline isn’t definitive, it’s a wake-up call to nurture your gut-brain health now. Focus on rebuilding a resilient microbiome through a fiber-rich diet, fermented foods, regular movement, and quality sleep. Track memory changes, stay mentally active, and talk to your doctor about probiotics or personalized gut testing if you’re a frequent antibiotic user. Brain health is lifelong—treat it like it’s on a prescription too.

References

Mehta, R. S., Lochhead, P., Wang, Y., Ma, W., Nguyen, L. H., Kochar, B., Huttenhower, C., Grodstein, F., & Chan, A. T. (2022). Association of midlife antibiotic use with subsequent cognitive function in women. PLOS ONE, 17(3), e0264649. https://doi.org/10.1371/journal.pone.0264649