Probiotics are live bacteria that can colonise the gastrointestinal tract. Probiotic bacteria are often called ‘healthy bacteria’. Probiotics have been shown to grant health benefits. They can be found in naturally fermented foods, functional foods with specific bacterial cultures added or in supplement form. Scientific evidence supports the implementation of them into our diets. Probiotics have been demonstrated to support the recovery of antibiotic-induced diarrhoea, infectious diarrhoea and lactose intolerance. There is also evidence from studies focusing on using them to treat numerous conditions, such as gastrointestinal inflammation and weight loss. A promising line of research is the use of them in the treatment of mental health conditions, such as depression.
The probiotics exert health benefits on the host by altering the host’s microbiome. The human microbiome is all the microorganisms which reside on or in the human body. The human microbiome can be split into different categories, such as the skin microbiome, the oral microbiome and the gastrointestinal (gut) microbiome. The human microbiomes impact on human health has become more and more apparent in recent years. Although we often see microorganisms as something to be avoided or killed, our relationship with the healthy bacteria of the human microbiome is symbiotic. Individuals with a ‘healthy’ microbiome have reduced infections of the skin, stomach, gut and so on. Conversely, individuals with an ‘unhealthy’ microbiome are more prone to various health issues. Probiotics can help to encourage a healthier gastrointestinal microbiome by introducing beneficial bacterial cultures into the digestive system. If the probiotics are effective, then these healthy bacteria will begin to outnumber and replace ‘bad’ bacteria. However, there are food and supplementary products on the market making claims to be probiotics when there is insufficient evidence as to their benefits.
It has been shown that there is active communication between the brain and the gut microbiome. This is known as the gut-brain axis for short, or the bidirectional communication between the resident microbes of the gastrointestinal tract and the brain. The gut microbiome can affect brain function and health through vitamins, neurotransmitters and microbial metabolites which can affect brain activity, such as short-chain fatty acids. Owing to this, it is proposed that the gut microbiome can affect a person’s mental health.
Preliminary studies have shown that supplementation of probiotics as a monotherapy to treat patients with moderate clinical depression are effective and safe. Patients treated with the probiotics showed a significant improvement in mood, anhedonia (inability to feel pleasure), improvements to levels of anxiety and improvements to sleep. The main proposed mechanism for why probiotics can be used to treat depression is that they reduce the production of inflammatory markers. Overproduction of inflammatory markers has been repeatedly observed in patients suffering from depression.
Probiotic treatment for mental health conditions is an exciting line of research as it could give patients more treatment options. Probiotics have also shown minimal, if any, side effects in current studies. Owing to this, they may be a favourable treatment option for patients who have tried conventional therapies and experienced side effects. Further research will help to define the most beneficial bacterial species to use in probiotics as well as define the most beneficial dosage and length of treatment. Research also needs to be carried out to show if probiotics are an effective adjuvant treatment which can be used in conjunction with traditional mental health medication.
For more information please refer to the articles linked below:
Health Benefits of Probiotics: A Review
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4045285/
The Efficacy, Safety, and Tolerability of Probiotics on Depression: Clinical Results From an Open-Label Pilot Study
https://www.frontiersin.org/articles/10.3389/fpsyt.2021.618279/full
Relationship between the gut microbiome and brain function
https://academic.oup.com/nutritionreviews/article/76/7/481/4985887?login=false
The effects of probiotics on depressive symptoms in humans: a systematic review