Antibiotic use among healthy older adults not tied to incident dementia, cognitive decline

Key takeaways:

• Antibiotic use did not increase risk for dementia or cognitive decline among healthy Australian adults aged 70 years or older.
• Higher frequency and long-term antibiotic use did not affect these associations.

Antibiotic use was not associated with incident dementia, cognitive impairment with no dementia or accelerated cognitive decline among a large cohort of healthy Australian older adults, according to a post-hoc analysis of the ASPREE trial.

The study was published in Neurology, the medical journal of the American Academy of Neurology (AAN).

“Antibiotics have been found in previous research to disrupt the gut microbiome, which is the community of tiny organisms that live in our intestines and support digestion,” Andrew T. Chan, MD, MPH, study author and a professor of medicine at Harvard Medical School, said in an AAN press release. “Because the gut microbiome has been found to be important for maintaining overall health, and possibly cognitive function, there was concern that antibiotics may have a harmful long-term effect on the brain.

“Given that older adults are more frequently prescribed antibiotics and are also at higher risk for cognitive decline, these findings offer reassurance about using these medications,” he continued.

To investigate the association between antibiotic use later in life and the subsequent risk for long-term cognitive decline and dementia, Chan and colleagues analyzed data from 13,571 healthy Australian adults aged 70 years or older (mean age, 75 years; 54.3% women) who were free of major cognitive impairment and independence-limiting physical disability when enrolled in the extended Aspirin in Reducing Events in the Elderly (ASPREE) trial, known as ASPREE-XT.

The researchers categorized participants as being users or nonusers of antibiotics during the first 2 years of follow-up.

The primary outcome of the study was cognitive function; secondary outcomes included probable Alzheimer’s disease and mixed presentations of dementia.

Overall, 62.5% (n = 8,481) of participants used any antibiotics at least once from trial enrollment to the second annual follow-up visit, according to the researchers.

After a median follow-up of 4.7 years, the researchers documented 461 cases of incident dementia (antibiotic users, n = 289; nonusers, n = 172) and 2,576 cases of incident cognitive impairment with no dementia (antibiotic users, n = 1,626; nonusers, n = 950).

Using Cox proportional hazards models, the researchers found that, after adjustment for baseline Modified Mini-Mental State Examination z score and sociodemographic factors, antibiotic use was not associated with incident dementia (HR = 1.06; 95% CI, 0.88-1.28) although it was associated with a slightly increased risk for cognitive impairment with no dementia (HR = 1.09; 95% CI, 1.01-1.18).

After additional adjustment for other risk factors including family history of dementia and use of drugs known to affect cognition, they found that there was no association between antibiotic use and cognitive impairment with no dementia (HR = 1.02; 95% CI, 0.94-1.11).

The associations between antibiotic use and dementia or cognitive impairment without dementia did not differ by frequency, duration or classes of antibiotic use, according to the researchers.

In a related editorial, Wenjie Cai, a PhD student, and Alden L. Gross, PhD, an associate professor in the department of epidemiology, both at Johns Hopkins Bloomberg School of Public Health, noted that the population in ASPREE-XT is even more homogenous than that in the ASPREE trial, which may limit the generalizability of the findings.

“For instance, the participants in the study by Wang et al. were healthy older individuals older than 70 years, and almost all of them were white and the baseline prevalence of diabetes and chronic kidney disease was lower than that of the general population in Australia, despite a higher prevalence of hypertension,” Cai and Gross wrote.

“[Nonetheless,] this study offers insights for clinicians and health care providers working with healthy older adults who share similar health profiles with those in this study,” they added.

References:

• Cai W, et al. Neurology. 2024;doi:10.1212/WNL.0000000000210255.
• Good news for seniors: Study finds antibiotics not linked to dementia. https://www.aan.com/PressRoom/Home/PressRelease/5220. Published Dec. 18, 2024. Accessed December 19, 2024.