Could Antibiotics Be Causing Mental Decline?

May 8, 2022

Could our guts affect how smart we are? A new study of over 14,000 women provides evidence. The study followed middle aged, 50-60 year old women over seven years from 2014 to 2018. It found that the longer a person used antibiotics, the greater the mental decline. At the high end, two months of antibiotic use was correlated with a mental decline equal to aging an extra 3-4 years.

This study does not imply causation. All participants self-reported their data, meaning they answered questionnaires. This does not allow scientists to see a direct cause-effect relationship. Other confounding effects may have been in play. One is that participants who used more antibiotics were more likely to have been sick. The scientists in charge of this study attempted to account for these differences. Study scientists adjusted for:

  • Age and socioeconomic factors (education level, spousal education level)
  • Lifestyle  (smoking, alcohol use)
  • General health (weight, physical activity, eating habits, multivitamin use)
  • Mental health (depression, antidepressant use)
  • Cardiovascular health (heart medication, blood pressure, cholesterol, history of heart attack)
  • Other big health issues (stroke, diabetes, emphysema)

After this they still found that antibiotic use was the leading indicator of mental decline.

The link between the gut and the brain is an area of intense and active investigation. Information can travel back and forth between the gut and the brain along a special route called the gut-brain-axis. This takes advantage of a large nerve, the vagus nerve. The vagus nerve directly links the digestive tract and the brain. Animal studies show that altering the gut bacteria can alter a host of mental processes. In developing animals, reducing gut bacteria alters how their brains develop. Animal stress hormone levels also vary in response to changes in gut bacteria levels. Several of these changes reverse or decline when normal bacterial levels are restored. More experimental information could help solidify the link between the gut and the brain.

Mehta, R. S., Lochhead, P., Wang, Y., Ma, W., Nguyen, L. H., Kochar, B., … & Chan, A. T. (2022). Association of midlife antibiotic use with subsequent cognitive function in women. Plos one, 17(3), e0264649.


Carabotti, M., Scirocco, A., Maselli, M. A., & Severi, C. (2015). The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Annals of gastroenterology: quarterly publication of the Hellenic Society of Gastroenterology, 28(2), 203.

Heijtz, R. D., Wang, S., Anuar, F., Qian, Y., Björkholm, B., Samuelsson, A., … & Pettersson, S. (2011). Normal gut microbiota modulates brain development and behavior. Proceedings of the National Academy of Sciences, 108(7), 3047-3052.

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