Webinar Recap: The Microbiome and Mental Health
Can we lessen the likelihood of getting psychiatric disorders? Understanding the role in mental health played by the microorganisms that live in our gut and elsewhere in the body may be one key for certain subsets of individuals, says Dr. Christopher Lowry, Associate Professor in the Department of Integrative Physiology at the University of Colorado Boulder.
In a webinar broadcast by the Foundation on July 11, 2017, Lowry, recipient of Young Investigator grants in 2010 and 2007, described how microorganisms in the body affect our response to stress, possibly promoting or protecting us against symptoms of certain disorders. He referred to studies that have reviewed the results of multiple other studies – called meta-analyses – of how inflammation might be related to depression, schizophrenia, PTSD and other psychiatric disorders. “Most of these studies have found evidence for low-grade chronic inflammation, but I would suggest that’s really just the tip of the iceberg,” he said.
The Microbiome and Inflammation
Some 500 to 800 species live on and inside the human body, and are most populous in the large intestine or colon. The Yanomami, hunter-gatherers in the upper Amazon, have the most diverse microbiome known today. Stress and a diet of fewer kinds of plants has likely cut the diversity of the microbiome in most of us.
What Lowry calls “Old Friends,” a set of microorganisms that include some sold as “probiotics,” co-evolved with humans, suppressing the immune response in ways we came to need. Another anti-inflammatory group he termed “Old Infections” date back to the hunter-gatherer period, including those caused by a bug called H. pylori. A third group sometimes called “pseudo commensals” are harmless denizens living in mud, untreated water and fermenting vegetables. “Our exposure to all of these classes of organisms has been reduced in modern urban societies,” Lowry said.
According to the “hygiene hypothesis,” when young children aren’t exposed to enough of these microorganisms they end up with too few regulatory T cells, which normally function to suppress the activity of other cells in the immune system.
With too few of these regulatory T cells, we may end up with chronic low-grade inflammation--or more generally, a disordered immune response to stress, Lowry explained.
Like stress, immune dysfunction has been tied to mental ill-health. People with autism, depression and PTSD all tend to have fewer regulatory T cells, according to Lowry. People with PTSD also have a higher risk of autoimmune disorders.
In one study Lowry mentioned, Marines at boot camp with higher concentrations of C-reactive protein (CRP) in the blood, a sign of inflammation, were more likely to develop PTSD symptoms after deployment.
The frontier is to find the specific microorganisms needed to protect against unhealthy immune activity. In a study with colleagues in South Africa, Lowry’s team found, for example, that among a group of people in South Africa exposed to trauma, certain microorganisms in the gut were linked to lower rates of PTSD.
The Value of “Orange Slime”
In the early 1970s, the British researcher John Stanford and his colleagues noticed that vaccines against leprosy were most effective in an area around Lake Kyoga in Uganda. “The shores of the lake were lined with “orange slime,” Lowry said. The slime turned out to be M. vaccae, a close relative of the species, M. leprae, that causes leprosy.
To test how M. vaccae affects the stress response, Lowry conducted a mouse experiment with Dr. Stefan Reber, now at the University of Ulm in Germany. The team injected whole heat-killed M. vaccae three times into mice prior to them being subjected to stress caused by a bullying, dominant male. It turned out that the animals became less submissive after the injections—less likely to turn up their tails and more likely to chase or attack the dominant male. That response is desirable, he explained, noting that in humans, a “passive or subordinate response during trauma [is]associated with an increased risk for PTSD later on.”
In the resilient mice, M. vaccae tended to stabilize the diversity of the gut microbiome after stress. Meanwhile, in stressed mice the Helicobacter family of bacteria spiked up. The stressed mice also tended to develop inflammation in the colon. Although the injections didn’t prevent the Helicobacter spike, they did seem to attenuate or prevent colitis, by prompting an increase in the secretion of interleukin-10, an anti-inflammatory molecule. Without the injections, the stressed mice experienced increases in interleukin-6, a pro-inflammatory immune molecule. Interestingly, depressed people also show increases in interleukin-6. (31:35-46.02)
Can people with psychiatric conditions help themselves by trying to reduce inflammation through diet? Lowry says yes. The more different types of plants you eat, the higher your gut microbiome diversity is likely to be. Drinking at least one alcoholic drink a week also promotes diversity and eating fermented foods like yoghurt and kombucha may help. One tip: Eating a hamburger leads to a surge in inflammation but adding a slice of avocado suppresses it. Exercise and sleep are also important, he said.
--Temma Ehrenfeld, science writer