A study involving a total of 14,542 women has found an as-yet-unexplained link between taking antibiotics for at least two months in midlife, and a dip in cognitive score assessments taken several years later.
The team behind the research, led by epidemiologists from Harvard Medical School in Massachusetts, says it shows how important it is to carefully monitor antibiotic use – and also how important it is that we understand the link between what's going on in our guts (which antibiotics can affect) and what's happening in our brains.
Plenty of previous studies have highlighted the link between the gut microbiome and the brain, but it's not clear exactly what the relationship might be. This new research adds more data points in a much-needed field of study.
"In a cohort of over 14,000 women, we observed that antibiotic use in midlife was significantly associated with subsequent poorer scores for global cognition, learning, and working memory, and psychomotor speed and attention," write the researchers in their paper.
"To our knowledge, our study represents the first large study of chronic long-term use of antibiotics and subsequent cognition."
The women in the cohort (a long-term chronic disease research project called Nurses' Health Study) had taken antibiotic drugs for a variety of reasons, including for respiratory infections, dental problems, acne, and urinary tract infections.
For those on antibiotics, the resulting drop in brain power across the various categories of learning, response, and memory was the equivalent of about three or four years of normal aging, according to the data.
Cognitive ability was assessed an average of seven years after the antibiotic use began, through an online test the participants completed at home. The test includes four different tasks in total, designed to measure different aspects of cognitive performance.
"This relationship was associated with longer duration of antibiotic use and persisted after adjustment for many potential confounding factors," write the researchers.
As usual with studies such as this, the link isn't enough to prove causation – that is, the data don't show it's definitely antibiotic use that's leading to a drop in cognition. It's possible that the conditions the antibiotics were intended to treat, rather than the antibiotics themselves, caused this small drop in cognition, for example.
However, there is enough here to suggest that more research is definitely warranted. The limitations of this study are that it didn't look at any particular type of antibiotic and that it relied on self-reporting for antibiotic use. However, the large sample size and the factoring in of other variables, including diet and other medications, increase its value.
Investigations into the link between antibiotics, gut microbiome, and brain function will continue, but to date, this is one of the best studies we've got looking at the potential long-term effects in adult human beings.
"Given the profound effect of antibiotic use on the gut microbiome – with prior studies showing alterations in functional potential at two and four years after antibiotic exposure – the gut-brain axis could be a possible mechanism for linking antibiotics to cognitive function," write the researchers.
The research has been published in PLOS One.