The Chemistry Column

Endorphins or ‘outdoorphins’?

Claire Gormley

Urban living has its perks— most things that you need are just a few steps from your door —but the stress levels of those living in urban environments have also been found to be significantly higher than those living in nature (Lowry et al, 2016). Exercise and going outside are two of the most common suggestions made to people who are looking to de-stress and relax. Not only does exercise physically remove one from a situation that may be causing stress, but it is widely known that exercise releases endorphins which make us feel better. Getting these endorphins pumping isn’t always easy, however, and recent studies into the stress levels of urban versus rural inhabitants point to spending time in nature rather than in the gym.

Endorphins are the body’s natural painkillers. Also referred to as endogenous opioids due to the sedative effect they have in common with opiates found in nature, these chemicals leave us feeling relaxed and optimistic after a significant sweat (Grossman and Sutton, 1985; Basso and Suzuki, 2017). They work in two different ways. Some endorphins bind to opioid receptors in the peripheral nervous system and prevent the release of substance P, which is a neuropeptide (a chemical messenger like a neurotransmitter) responsible for sensing pain (Chaudhry and Gossman, 2021). Others can also bind to receptors in the central nervous system and suppress the release of the neurotransmitter gamma aminobutyric acid (GABA). The suppression of GABA consequently increases the production of dopamine, the pleasureinducing neurotransmitter, leading to an increase in mood (Chaudhry and Gossman, 2021).

This pathway makes sense to me: the receptors on our neurons help us to experience the world around us, including pain, and accepting that the absence of pain is pleasure is not a far jump to make. What I find more surprising is how going outside produces the same effects. There is some evidence that interaction with plants reduces our psychological stress through the suppression of our sympathetic nervous system (a part of a nervous system that autonomously coordinates our involuntary actions, like breathing and heart rate); however, a different study suggests that it may be the microbes in our gut that actually soothe our stress (Lee et al, 2015; Foxx et al, 2020).

According to Foxx et al (2020), Mycobacterium vaccae, along with other soilbased bacteria that have anti-inflammatory and immunoregulatory properties, may be effective stress relievers. These ‘outdoorphins’ flood our bodies when we interact with plants and soil outdoors, and act as natural antidepressants by reducing inflammation caused by stress-related psychiatric disorders (Nazish, 2018; Lowry et al, 2016). The mechanism by which M. vaccae brings about these positive changes in our mood is not well understood yet; however, it is thought that T- cells, which are immune cells responsible for regulating our inflammatory response, are signaled by the microbes to effect this change (Lowry et al, 2016). Further studies are being conducted into how these microbes can be used to treat people suffering from posttraumatic stress disorder (Foxx et al, 2020).

As an urban dweller returning from a countryside holiday, I am grateful that a bit of soil and some new green friends are all the medicine that I’ll need the next time the city pressure rises.

References

Basso, J. C., and Suzuki, W. A. (2017) ‘The Effects of Acute Exercise on Mood, Cognition, Neurophysiology, and Neurochemical Pathways: A review’ in Brain Plasticity, 2(2): 127-152

Chaudhry, S. R., and Gossman, W. (2021) Biochemistry, Endorphin. Treasure Island: StatPearls Publishing

Foxx, C.L., Heinze, J.D., González, A., Vargas, F., Baratta, M.V., Elsayed, A.I., Stewart, J.R., Loupy, K.M., Arnold, M.R., Flux, M.C., Sago, S.A., Seibler, P.H., Milton, L.N., Lieb, M.W., Hassell, J.E., Smith, D.G., Lee, K.A.K., Appiah, S.A., Schaefer, E.J., Panitachpakdi, M., Sikora, N.C., Weldon, K.C., Stamper, C.E., Schmidt, D., Duggan, D.A., Mengesha, Y.M., Ogbaselassie, M., Nguyen, K.T., Gates,. C.A., Scnabel, K., Tran, L., Jones, J.D., Vitaterna, M.H., Turek, F.W., Fleshner, M., Dorrestein, P.C., Knight, R., Wright, K.P., and Lowry, C.R. (2020) ‘Effects of Immunization with the soilderviced bacterium Mycobacterium vaccae on stress coping behaviours and cognitive performance in a “two hit” stressor model’ in Frontiers in Physiology, 11:524833

Grossman, A., and Sutton, J.R. (1985) ‘Endorphins: What are they? How are they measured? What is their role in exercise?’ in Medicine and Science in Sports and Exercise, 17(1): 74-81

Lee, M., Lee, J., Park, B., and Miyazaki, Y. (2015) ‘Interaction with indoor plants may reduce psychological and physiological stress by suppressing the autonomic nervous system activity in young adults: a randomized crossover study’ in Journal of Physiological Anthropology, 34(1): 21

Lowry, C. A., Smith, D. G., Siebler, P. H., Schmidt, D., Stamper, C. E., Hassell, J. E. Jr., Yamashita, P. S., Fox, J. H., Reber, S. O, Brenner, L. A., Hoisington, A. J., Postolache, T. T., Kinney, K. A., Marciani, D., Hernandez, M., Hemmings, S. M.J., Malan-Muller, S., Wright, K. P., Knight, R., Raison, C. L., and Rook, G. A.W. (2016) ‘The Microbiota, Immunoregulation, and Mental Health: Implications for Public Health’ in Current Environmental Health Reports, 3, 270-286.

Nazish, N. (2018) T’hink you don’t need houseplants? Science says different’ in Forbes, 10/02/2018. www.forbes.com/sites/nomanazish [accessed 11 February 2022]