Microbiome, Stress and Anxiety

If you’ve read the blog posts Microbiome and COVID-19 and Food for the Microbiome you’ll realise the power of the microbiome to affect many aspects of health. You’ll also be aware that what we eat affects the balance of organisms in the microbiome. Here we’ll look at the interactions between the gut microbiome and brain health, in particular stress and anxiety in wild animals and humans.

Squirrels and Stress

A link between stress and unhealthy microbiomes has been discovered in wild squirrels. Researchers tested squirrel microbiomes and analysed the animals’ stress hormones. Red squirrels living in a low-stress environment were found to harbour healthier, more diverse communities of micro-organisms in their guts than their stressed counterparts. The greater the stress in the squirrels, the less bacterial diversity they had. The researchers captured the same squirrels two weeks later, and found that if stress levels increased, some potentially harmful bacteria also increased (1).

Bacterial diversity within animals and humans is emerging as a key factor in health. This study shows there is a link between low stress and a diverse microbiome in animals living in the wild.

Anxiety and the Microbiome

Studies have shown that as many as a third of people will be affected by anxiety symptoms during their lifetime. Anxiety symptoms are common in people with mental diseases, stress and some physical disorders.

It’s well established that the gut microbiota plays a key role in modulating the immune system and metabolism by providing inflammatory mediators, nutrients and other metabolites. It is now increasingly apparent that the gut microbiota can help regulate brain function through the gut-brain axis. Recent research suggests that mental disorders could be treated by regulating the intestinal microbiota.

A review of 21 studies suggests a link between the gut bacteria and mental disorders. More than half the studies found that regulating the gut microbiota in some way had a positive effect on anxiety symptoms. Overall there was more success where there were dietary changes rather than using probiotics alone.

In short, the good news is that regulating the intestinal microbiota could be used to alleviate mental health problems, such as anxiety, alongside other treatments (2).

References

1. Biology Letters, January 2015. Stress and the microbiome: linking glucocorticoids to bacterial community dynamics in wild red squirrels. Stothart MR et al.

2. General Psychiatry, 2019; 32: e100056. Effects of regulating intestinal microbiota on anxiety symptoms: A systematic review. Yang B et al.