Depression And The Human Gut Microbiota

Introduction

Depression is one of the most common, often recurrent wide-ranging disorder responsible for disability in humans worldwide. The causation of depression has been found to involve the dysregulation in neuroendocrine (hormonal), neurotransmitter, and metabolic systems. Over the years, there has been enough evidence pointing towards the role of gut microbes in neural development and function. Together, the intestinal bacteria represents a virtual organ of sorts inside of us with almost 100 times more genetic material present in all the cells in our human body. But the classification of all the microbes present in our body is incomplete as about 60% of these microbes cannot be grown in a lab for studies.

There is a harmony that is established in the gut between our own internal system and the gut microbes which when disturbed is thought to be the cause of many disorders in human beings from obesity to inflammatory bowel diseases. Even though the role of gut microbes in neurological conditions has not been well established, there has been a rapid increase in evidence which underlines the possibility that changes in the gut microbial environment have an effect on the normal functioning of our nervous system. Hence, our gut environment can have a major role to play in our mood and also in depression.

Gut microbiota and its relationship with the brain in humans

There exists a bidirectional communication between our gut microbiota and the components of the gut-brain axis which can influence the normal functioning of the gut and may contribute to a risk of diseases in humans. Changes in gastrointestinal (GI), autonomic nervous system (ANS), immune system, enteric (intestinal) nervous system (ENS), and central nervous system (CNS) brought about by the microbiota can lead to alterations in the following :

  • GI barrier function
  • Fat storage and energy balance
  • Increased stress reactivity
  • General low-grade inflammation (GI and systemic)
  • Depressive-like behaviors and increased anxiety

All the above-mentioned mechanisms are found to be involved in the development of mood and anxiety disorders in humans.

The case for the role of microbiota in human cognition, mood, and emotion.

The vast number of bacteria which constitute the intestinal microbiome are engaged in interactions with each other as well as its local environment in a balanced manner to achieve the normal functioning of our body. They produce a wide range of biologically and neuroactive (acting on the nervous system) molecules complete with neurotransmitters and an extensive set of short chain fatty acids which are produced through fermentation, all of which have known and unknown effects on the nervous system.

These direct and indirect effects of the intestinal microbes on the intestinal tissues, local immune system and their components, and the enteric (intestinal) nervous system, affect the neuronal pathways of our brain. The above-mentioned processes together influence our mood and cognition by acting upon the components of our neural system and increasing evidence points to a strong relationship between our intestinal health and our mental well being.  

Depression is associated with altered gut microbial composition, richness, and diversity. In a study conducted where the researchers transplanted the microbiota signature found in depressed patients to rats whose own microbiota was purposefully depleted, this procedure induced the development of some of the behavioral (anxiety, anhedonia) and physiological features of the depressive state.    

Studies have also shown the impact of early life stress in remodelling the gut microbial composition. Subtle changes in microbial acquisition and maintenance during the vulnerable early life period may contribute to the predisposition of the individual to stress-related disorders in the adulthood. This can be a result of the effect of these subtle changes in our microbiome on the neuro signalling pathways of the brain-gut microbiota axis.

There is growing evidence suggesting the role of our intestinal microbes in neural development both centrally in the brain and in the enteric nervous system and hence pointing towards healthy interventions since birth till the formative years to maintain a healthy mind and body. Depression is characterized by alterations in the gut microbiota and hence we need to understand our gut so as to ensure a healthy functioning of our bodily systems. And this provides us with an insight which shines a new light on how we perceive health itself.

This gives us more tools in treating depression and other disorders of the brain in the perspective of our gut. By sequencing your microbiome with consumer testing like Thryve, you’ll be able to gain more insights into how each of these microbes may contribute to your mood. Probiotics have also shown in studies to reverse negative emotions and enforce positive thinking. All in all, this should be enough to give us a whole new meaning to the quote: “You are what you eat.”  

References

Disclaimer: The above article is sponsored by Thyrve, the world’s first Gut Health Program that incorporates microbiome testing and personalized probiotics to ensure a healthier gut, happier life, and a brighter future.