Do Bacteria Make you Anxious?


Anxiety is a growing problem in modern life. According to the National Institute of Mental Health (NIMH), 18% of the adult population in the United States is affected.


Now, a new study has found that when it comes to anxiety, the gut could play a major role.


In a study published in the journal Microbiome, researchers from the APC Microbiome Institute at University College Cork report that the absence of gut bacteria in mice changed the expression of microRNAs (miRNAs) in regions of the brain that play a role in anxiety and depression.


How was the study conducted?


The researchers compared three groups of mice:

  1. Germ-free mice, which had no gut and were raised in an environment with no microorganisms.
  2. Ex-germ-free mice, which were raised germ-free then had gut bacteria introduced.
  3. Mice with normal gut bacteria and bred under normal conditions.


The team noticed that mice bred in germ-free conditions were more likely to develop anxiety and depression, have social issues and cognitive dysfunctions.  


MicroRNAs are known to be important in the regulation of the nervous system, so the researchers sought to analyze the miRNAs in the various groups of mice.


Compared to normal mice, the germ-free mice had differences in 103 miRNAs in the amygdala (processes emotions) and 31 miRNAs in the prefrontal cortex (involved in behavior and impulse control).


Notably, when researchers reintroduced gut bacteria into the germ-free mice, some of the miRNA differences disappeared.


The team concludes that a healthy gut microbiome is important for normal miRNA regulation, which is fundamental to a healthy brain and nervous system.


In addition, the researchers found that treating rats with antibiotics caused similar changes as seen in the germ-free mice, suggesting that altering gut bacteria in adulthood could change miRNAs in a manner that causes anxiety.