Gardening and working with plants are long known for their relaxing and calming effects. But is there more to it than the simple joy of light physical work and putting your mind where your hands are? Researchers say there is. The vast microbiome of soil includes certain species of bacteria that are able to boost our mood, lower our stress levels and improve our immune system. Some other species can indirectly benefit us by slightly triggering our immune response – “training” our immune system. The microbes we encounter in the wild, as well as our own microbial communities in the gut, affect not just our physical but also our mental health in a number of ways.
Why do we need microbes?
Microorganisms colonize our bodies. Whether we like them or not, they play an important role in our ability to process food, fight diseases, and feel good. Research conducted over the last couple of decades revealed a complex relationship between us and our microscopic friends and foes. Every individual has their unique DNA, but also a unique microbiome. There is a good reason why the Human Genome project was soon followed by the Human Microbiome Project.
The human genome contains 20.000-25.000 genes. That is about as much as a Japanese gecko, and about 8 times less than wheat. If we are the most complex living organisms, how could our genetic code be so humble? Well, if we add the organisms living within and on us into the equation, the answer gets a bit clearer. We didn’t have to take the slow, painstaking road and learn to do things ourselves since we could easily employ microbes to do it for us. We offer them food and a cozy place to live, in return, they offer us a wide array of services.
The estimated number of genes in our microbiome is hanging around an astonishing 232 million genes. Although only a small portion of those genes has something to do with us, that something is very important. Some of those genes encode functions that enable bacteria to process food and make previously unavailable nutrients available to us. Others enable bacteria to produce compounds that affect the activity and concentration of chemical messengers in our bodies – hormones.
The decline of microbial diversity
By moving into urban environments, we lost contact with the microbial diversity we once encountered every day spending time in nature, working with plants, and, quite literally, playing in the mud. We reduced the risk of numerous pathogens and parasites common in the natural environment but lost our microbial friends along the way. In addition, the widespread use of antibiotics and antimicrobial cleaning products only worsened the situation, killing beneficial microorganisms and creating resistant pathogens. Becoming estranged from our microbiome came at a great cost, and we are still learning about its scope and effect. According to the WHO, about 280 million people are suffering from depression globally.
Low diversity of the microbiome means an unhealthy microbiome. The result is a state of dysbiosis which causes a myriad of health problems and diseases. Asthma, allergies, acne, chronic inflammation, type 2 diabetes, cancer, autoimmune diseases, depression, and anxiety can all stem from a simple microbial disbalance. The good news is – we can prevent the decline of our microbiome and reverse its negative effects.
Microbes and blues
Depression is a complex disease that can manifest in a variety of symptoms and has various shades. It rarely has a single origin, but certain elements contribute to its development and severity more than others. The composition of our microbiome is one of those elements, playing a pivotal role in our susceptibility to depression. In a study, healthy mice were given a fecal transplant from an individual that has Major Depressive Disorder (MDD). All the mice that were given the MDD transplant developed depressive behavior. However, another study concluded that the microbiome of mice that have suffered from stress and depression has lower diversity and content, indicating that the connection between the microbiome and mental health is bidirectional.
But why? How can the disbalance of the microbiome have an effect on one’s mental health? Scientists have only started to tackle the details of our relationship with the microscopic world within, so we still don’t fully understand the dynamics. The current theory suggests that the inflammation of the gut resulting from dysbiosis is the reason why. The gut contains about 500 million neurons, and it is highly connected to the brain. When inflammation occurs, the body responds by releasing certain compounds, like cytokines, which can induce depressive effects. Another explanation is that the inflammation of the gut can spread onto the nerves themselves, activating certain pathways that alter the chemistry of the brain.
We are only starting to explore the depths of the perplexing relationship between us and our microbiome, and many questions are yet to be answered. However, the empirical data remains unambiguous – the content and the diversity of our gut microbial community affect us physically and mentally. After all, there is a reason why the gut is called the second brain.
Can natural solutions work as good as Prozac?
Millions of people struggling with depression are prescribed antidepressants to mitigate the chemical imbalance that is wreaking havoc in the brain. Many times these medications can be lifesavers, but their use comes with side effects that can be quite severe. In a quest to find safer and more effective alternatives, researchers have stumbled upon a peculiar bacterium with some amazing properties. The story begins in a village in north-central Uganda, where the locals found a mysterious muddy substance that can cure a variety of diseases. A detailed investigation revealed that the main healing agent of this substance is a single species of bacterium – Mycobacterium vaccae.
Mycobacterium vaccae is a saprophytic, non-pathogenic soil microbe that has immunoregulatory and anti-inflammatory effects. The origin of its magic lies in its ability to inhibit cytokine responses. Cytokines are small proteins that activate our immune system when we are under attack. Various cells can produce them and there are many different types. These proteins play a pivotal role in our immune response, but when there’s too much of them or the “bad” ones are dominant, they inflict damage to our cells. By inhibiting the overactivity of cytokines, M. vaccae successfully reduces inflammation and the accompanying negative effects. Having such a general mode of action, it can treat a wide array of diseases. Its effects are most prominent in the treatment of allergies, arthritis, asthma, skin conditions caused by inflammation, tuberculosis, and depression.
Immunizing against depression
Mycobacterium vaccae is a promising new tool to battle depression without the unpleasant and sometimes dangerous side effects of conventional antidepressants. It is very powerful and effective for this particular condition, as it can affect the activity of neurotransmitters. In addition to its cytokine inhibiting action, M. vaccae can also trigger certain neurons and stimulate serotonin production. When serotonin levels increase, the feelings of anxiety and fear start to fade away, and stress resilience improves. Moreover, M. vaccae also stimulates the activity of the microbiome, improving and making it more resistant. By targeting both the inflammation and the neural activity in the brain, M. vaccae offers an effective and holistic way to put things back in balance and get rid of depression for good.
This bacterium isn’t a stranger to immunotherapy and its beneficial effects are already utilized in the treatment of allergies and cancer. However, its effects on the psyche caught the attention of researchers fairly recently. A study conducted in 2007 at the University of Bristol brought scientific attention to the potential of M. vaccae in depression treatment. The research group led by Christopher Lowry immunized lab mice with heat-killed M. vaccae in order to investigate its effects. The results have shown that M. vaccae activated the neurons producing serotonin and improved stress-coping mechanisms. Such an incredible discovery raised a lot of dust in the scientific community. As a result, a number of papers have been published on the topic since then, gradually revealing the clockwork behind its mode of action and its potential to treat other mental health problems.
Wonders of nature are truly endless. With the help of a simple soil microbe, we might soon have a vaccine that could cure millions of people, and prevent depression in many more. However, we don’t have to wait for our dose of M. vaccae and other beneficial microbes. We can get them in our gardens, by working with soil and taking care of our beloved plants. So don’t hesitate to take off the gloves and get your hands dirty. It can bestow you with the much-needed relief and serotonin boost to persist in these trying times.
- Limbana, T., Khan, F., and Eskander, N. (2020). Gut Microbiome and Depression: How Microbes Affect the Way We Think?
- Rook, G., Raison, C., and Lowry C. (2012). Can we vaccinate against depression? Drug Discovery Today, Vol 17, No. 9/10.
- Hassell, J., Fox, J., Arnold, M., Siebler, P., Lieb, M. Schmidt, D., Spratt, E., Smith, T., Nguyen, K., Gates, C., Holmes, K., Schnabel, K., Loupy, K., Erber, M., Lowry, C. (2019). Treatment with a heat-killed preparation of Mycobacterium vaccae after fear conditioning enhances fear extinction in the fear-potentiated startle paradigm. Brain, Behavior, and Immunity, Vol. 81, pp. 151-160.
- Foxx, C. L. et al. (2020). Effects of Immunization With the Soil-Derived Bacterium Mycobacterium vaccae on Stress Coping Behaviors and Cognitive Performance in a “Two Hit” Stressor Model. Frontiers in Physiology.
- Lowry, C.A. et al. (2007). Identification of an immune-responsive mesolimbocortical serotonergic system: Potential role in regulation of emotional behavior. Neuroscience. May 11; 146(2-5): 756–772.