The vegetable garden
Contact with the soil is good for health. By working in the garden and coming into contact with soil, you encounter bacteria. Children pick up microbes by getting ‘dirty’. Most people no longer have a vegetable garden, but you can start a small vegetable garden by replacing grass, paving stones or gravel with good soil.
There are several reasons why gardening is healthy. Vegetables
and herbs contain minerals and nutrients. You are physically active. Winter depression and the happiness when the sun starts shining and you can work in the garden again have to do not only with vitamin D, but also with bacteria. Contact with bacteria contributes to healthy gut flora. Many bacterial species that live in the soil are also found in our gut. Freshly picked vegetables contain beneficial bacteria; you do not need to wash your own vegetables (as long as you do not use pesticides). You can also inhale bacteria while working with the soil.
Evolution
Humans evolved together with microbes. Intestinal bacteria protect their host and are important for the functioning of immune cells; they influence our behaviour and emotions. Healthy microbes that live in the soil can inhibit inflammation and increase the serotonin level in the body. One example is Mycobacterium vaccae, a bacterium related to the organism that causes tuberculosis. Vacca means cow; the bacterium was given this name because it was first cultured from cow manure in Austria. These non-tuberculous mycobacteria also live in manure, compost and soil. M.vaccae affects the brain (via the gut-brain axis) and can itself produce serotonin. Serotonin is a brain hormone that is produced mainly in the gut and has a positive effect on our moods.
Happiness
Mycobacterium can be administered as an antidepressant; it reduces depression and anxiety. Matthews and her colleague Jenks gave M.vaccae to mice. As a result, the animals navigated through a maze twice as fast, experienced less anxiety and made fewer mistakes. The antidepressant effect of these soil bacteria remains noticeable for three weeks.
The bacteria stimulate immune responses. Injections with substances derived from M.vaccae can be used for tuberculosis. The bacterium reduces complaints that occur in Crohn’s disease and rheumatoid arthritis. Its use is said to have a beneficial effect on asthma, eczema and psoriasis.
The garden and the soil have much to offer. Other soil bacteria undoubtedly also influence our gut flora and may improve our mood. It appears that ill people and cancer patients experience less stress when they work in the garden; contact with bacteria will also play a role for them. If space is limited, you can also put a few containers on the balcony, which promotes contact with soil.
Sources
Matthews DM, Jenks SM. Behav Processes. 2013 Jun;96:27-35. Ingestion of Mycobacterium vaccae decreases anxiety-related behavior and improves learning in mice.
