Positive impact of running on gut microbiota and adolescent depression

Adolescence is a time when various mood disorders, including major depressive disorder (MDD), can occur. In recent years, many studies have examined the link between intestinal dysbiosis and depression. The problem is that most of these studies have been conducted in adults. An international team of scientists has therefore focused on adolescents and more specifically on the effects of sport on the intestinal microbiota of adolescents suffering from "subthreshold depression". This "borderline" depressive syndrome - which only meets part of the criteria for a major depressive syndrome - would affect 20 to 30% of adolescents and would be reflected by the presence of at least 2 symptoms characteristic of depression described by the manual of mental disorders (a depressed mood, fatigue, weight loss or gain, agitation or psychomotor slowing, feelings of guilt, etc.), for at least 15 days. These individuals have a 40% risk of eventually developing MDD.

Depressed schoolchildren put to the test

The researchers recruited 25 middle school students aged 12 to 14 years with submental depression and randomly assigned them to 2 groups: 

• a group running at a moderate pace (50 to 70% of maximum heart rate) 30 minutes a day, 4 days a week;
• a placebo group doing group activities (reading, singing and games) once a fortnight.

After 3 months of experimentation, the stools of all the volunteers were collected and analyzed by sequencing of the rRNA16S gene.
Results published in Psychiatry Research show that adolescents in the running group had significantly fewer depressive symptoms, whereas those in the reading and games group showed no improvement.

A signature of the intestinal microbiota

Analysis of the microbiota shows that, compared to the placebo group, the young runners had an increase in the relative abundance of certain bacteria:
Coprococcus and Blautia, bacteria that produce butyrate, a short-chain fatty acid (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) (SCFA) known for its health benefits, thanks to its anti-inflammatory action for example Dorea, and Tyzzerella: bacterial genera whose link with depression is not yet fully established. However, Tyzzerella had already been identified in smaller quantities in women suffering from postpartum depression.

Enrichment of certain metabolic pathways

Analysis of the runners metabolic pathways revealed that those involving defense and signal transduction mechanisms were strongly enriched, which could explain in part the antidepressant effect of running. 
The researchers also note that pathways associated with neurodegenerative diseases - some of which are known to be similar to those of major depressive syndrome - were depleted in runners.
While the results of this study need to be confirmed by a larger study, they represent a new step in understanding the function of the gut-brain axis and its role in mood disorders.