In the United States, around 22 percent of older people have cognitive impairment, while around 10 percent have dementia. A new study suggests that antibiotics aren’t associated with the two conditions. Published in Neurology, the journal of the American Academy of Neurology, the study shows that antibiotics are not connected with a raised risk of cognitive impairment or dementia in the short term.
“Older adults are more frequently prescribed antibiotics and are also at higher risk for cognitive decline,” said Andrew Chan, a study author and a professor of immunology and infectious diseases at Harvard Medical School, in a press release. “These findings offer reassurance about using these medications.”
Antibiotics, the Gut, and the Brain
Antibiotics have recently raised alarms for researchers studying two seemingly separate areas of the body: the gut and the brain.
“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,” Chan said in the 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.”
Specifically, the worry was that antibiotics were associated with cognitive impairment or dementia. While cognitive impairment is characterized by mild changes in thinking and memory, dementia is defined by dramatic changes in cognition — problems that disrupt a person’s day-to-day activities.
To tease out any associations between antibiotics and cognitive decline, the study authors observed older adults for several years, tracking their antibiotic use and their cognitive condition in the short term. Neither the amount, nor the type of antibiotics were associated with cognitive decline.
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Senior Science
The trick to the study was the selection of participants. Around 13,570 participants aged 70 years old or older, then without cognitive impairment or dementia, were selected to participate at the start of the study. Following their selection, the participants were told to complete a series of cognitive tests, including measures for memory and attention. The same tests were then repeated, first at a one-year interval, then at two-year intervals, for the remainder of the study.
In the first two years following their selection, the participants’ prescription records were watched to assess their use of antibiotics. Some participants — around 63 percent — were prescribed antibiotics in the two-year time period, while others weren’t prescribed antibiotics at all.
After the two-year period, the participants were studied for an average of five additional years. In that time, around 2,580 developed cognitive impairment, and around 460 developed dementia.
The study authors then compared the participants’ antibiotic use with their cognitive scores and outcomes, to see whether the amount or type of antibiotics that they used were associated with cognitive impairment or dementia. After adjusting for factors such as the participants’ cognitive status at the start of the study, as well as the participants’ predisposition to cognitive decline, the authors found that antibiotic use was not connected with a raised risk of cognitive issues.
Of course, the study followed participants for a short span of time, leaving space for future studies to follow participants for longer periods. Those studies, Chan said according to the press release, could untangle any long-term associations between antibiotic use and cognition. Until then, though, Chan’s study suggests that patients should rest-assured that their use of antibiotics isn’t a cognitive concern, at least in the short term.
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Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
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