Although it’s not a straight line that connects them, there is a bi-directional connection between your gut and your central nervous system. Think of this complex gut-brain axis pathway as a squiggly line that also connects to the endocrine, immune, and autonomic nervous systems.

When you consider the cells and organs in these various systems and their multiple functions and interactions with other cells, organs, and systems, it is no wonder that even the tiniest disturbance in any one area can cause your health to spiral for better or cascade for worse.

Although we have been researching the gut-brain axis for decades, during the past 10 or so years scientists have been making remarkable progress. Emerging research suggests there are many direct and indirect links between your gut health and your mental health – including depression and anxiety, and perhaps other conditions like schizophrenia and autism.1

To better understand this complex relationship, it is important to know the very basics concerning the development of the gut-brain axis:

  • The microbiome is defined as all the microorganisms in the human body and their respective genetic material. The microbiota is defined as all microorganisms in a particular location, such as the gastrointestinal tract or the skin.
  • An individual’s microbiome is first established in utero through the development and interactions with the placenta and amniotic fluid. Animal studies have found that stress imposed on an expecting mother can change the developing gut microbiota, and human studies have determined the method of delivery (vaginal or C-section) influences bacteria amounts and compositions.
  • The first week of life influences a baby’s gut microbiota development that can impact their entire life. Similarly, breastfeeding a child, compared to formula feeding, has beneficial long-term effects that include increases in helpful immunoglobins and decreases in pro-inflammatory cytokines. Cessation of breastfeeding and introduction of solid food is an impactful period that results in a baby’s microbiome resembling that of an adult.
  • Throughout life, dietary changes can have an impact on gut microbiota in as little as one day. In addition to foods and drinks, the environment, stress, antibiotic use, and other external influences shape and grow the diversity of the microbiome. In times of major microbial imbalance, the gut can become susceptible to increased intestinal permeability (known as leaky gut), which can start a cascade of inflammation and further systemic chaos throughout the bloodstream.

Scientists have focused their research efforts on these microbial fluctuations and have found links to the most common mental health issues we battle today.

Here is an update:

  • The chaos that ensues from increased intestinal permeability escalates rapidly. The molecules that escape the gastrointestinal tract through its weakened lining and into the bloodstream gather with other inflammatory biomarkers that are released into systemic circulation because of the brain’s ability to sense the insult happening in the gut. At this time, your blood is swarming with inflammatory biomarkers that have gone rogue.
  • These inflammatory species also have direct communication with the brain via self-produced neurotransmitters, as well as the vagus nerve receptors in the gut that control sympathetic reactivity.
  • The increased permeability that occurs in the gut can also happen at the blood-brain barrier, which is comprised of similar cells that become susceptible to damage with increases in inflammation. These inflammatory cells can leak into the brain and influence brain function, which is when you can begin to see links to anxiety, depression, and memory loss.

The majority of research in this fascinating field examines the effects of probiotics (and other nutrients) and their impacts on the microbiome, gut health, and mental health.

  • Beneficial bacterial species, including members of the Lactobacillus and Bifidobacteria families, can act to suppress this immune and sympathetic reaction.2 They have been shown to reduce both inflammation and anxiety, as well as behavioral signs of distress.
  • Researchers can now tell from a single stool sample whether a patient suffers from depression with almost 100-percent certainty.3
  • Major differences have been found between the oral microbiome of individuals with schizophrenia versus those who do not have it.
  • Ongoing research is looking into the connections between the microbiome and Alzheimer’s disease.
  • Although there are clear links between mental health and the microbiome, it is still important to remember how diverse mental health can be, and just how many factors can change and contribute to one’s microbiome, thus making research in this field immensely complex.

References
1.    Clapp M, Aurora N, Herrera L, et al. Gut microbiota’s effect on mental health: The gut-brain axis. Clin Pract  2017;7(4):987.
2.    Deans E. Microbiome and mental health in the modern environment. J Physiol Anthropol 2016;36(1):1.
3.    Naseribafrouei A, Hestad K, Avershina E, et al. Correlation between the human fecal microbiota and depression. Neurogastroenterol Motil 2014;26(8):1155-1162.