Tuesday, August 27, 2013

Nature’s Antidepressant – How working with the soil might boost your spirits

Have you been looking for an excuse to get your hands dirty? If so, here it is!

In 2002, Graham Rook and Laura Brunet published an article called “Give us this day our daily germs,” in which they argued that our modern-day lifestyles in wealthy countries, including both hygiene and antibiotics, have reduced our exposure to organisms, such as mycobacteria, that live in soil and water.

This reduced exposure, they suggest, is improperly activating our immune systems, resulting in higher rates of allergies and disease. And in the past ten years, many researchers have become interested in the ways that the human immune system is triggered by the world outside our bodies.

Bacteria improves quality of life in cancer patients
Of particular importance are some of the studies examining the effects of Mycobacterium vaccae (M. vaccae)—a strain of bacteria commonly found in soil. For example, while testing the effects of heat-killed M. vaccae on lung cancer patients receiving chemotherapy, oncologists made an unexpected discovery: 

The bacteria did not seem to affect patients’ survival rates, but patients did report an improved quality of life, including better cognitive function and a sense of vitality, as well as some relief of both the chemotherapy-related treatment symptoms and cancer symptoms. 

Bacteria in soil triggers release of serotonin 
Serotonin is vital to nearly all of our physical and behavioral processes, including mood regulation, and many common antidepressant drugs are designed to affect serotonin levels.

Neuroscientists at the University of Bristol decided to investigate the oncologists' findings further, and discovered that heat-killed M. vaccae altered emotional behavior in mice. Specifically, the bacteria produced antidepressant-like effects by triggering neurons in the brain to produce serotonin.

Chris Lowry, lead author of the University of Bristol study, in his conversations with the media, noted that such studies are leading to a better understanding of the connections between healthy immune systems and mental health. “They also leave us wondering if we shouldn’t all be spending more time playing in the dirt,” he also said.

Which leads me to ask:
Have you had your dose of M. vaccae today?

Stay tuned for my next post about how regular contact with M. vaccae might also make you smarter...

Lowry, C.A. et al. (2007). Identification of an Immune-Responsive Mesolimbocortical Serotonergic System: Potential Role in Regulation of Emotional Behavior. Neuroscience 146, 756-772.

Medical News Today. (2007, April 2) Soil Bacteria Work in Similar Way to Antidepressants. http://www.medicalnewstoday.com/articles/66840.php

O’Brien, M.E., et al. (2004). SRL172 (killed Mycobacterium vaccae) in addition to standard chemotherapy improves quality of life without affecting survival, in patients with advanced non-small-cell lung cancer: phase III results. Annals of Oncology 15(6), 906-914.

Rook, Graham and Brunet, Laura. (2002). Give us this day our daily germs. Biologist 49(4), 145-149.


  1. Hi!

    I'm really enjoying your blog. As a sometime-scientist, I enjoy reading mini-essays that incorporate scholarly research...

    One thing your writing has done for me is that it's made me feel that, even though we live in the city, the time my kids spend out in our little yard is still doing them physical and psychological good and is still important. Also, it made me realize why I hated the windowless office I briefly occupied for a while at my last job so much!


    1. Hi Tara, Thanks very much for your note. I'm glad you are enjoying the blog. I read a lot of the scholarly research about the human-nature relationship, and my simple hope is to make it available to more people (rather than this knowledge being stuck in the Ivory Tower!). So it's nice to hear that I've done so for at least one person. Also glad to hear you are no longer in a windowless office - that sounds miserable!