Could exposure to microorganisms in the dirt somehow protect us from anxiety, depression and post-traumatic stress disorder? Could our increasingly sterile, urban environments be partly to blame for rising rates of stress-related disease?
For nearly two decades, Integrative Physiology Professor Christopher Lowry has dedicated his career to exploring these once-controversial ideas. Now, with mounting research suggesting he’s been on the right track all along, he’s forging ahead with a dream of someday developing a bacterium-based immunization—or stress vaccine—to stem the rising tide of mood disorders.
“As human societies have migrated to urban environments, we have lost touch with a host of bacterial species that play a role in regulating our immune system, and this is helping to fuel an epidemic of inflammatory disease,” says Lowry. “I want to know: What are the impacts on mental health?”
Lowry was a research fellow at the University of Bristol in the early 2000s when he began to hear stories about Mycobacterium vaccae, a rare microorganism discovered in the soil on the shores of Lake Kyoga in Uganda. Scientists were perplexed by the fact that when given vaccines to prevent tuberculosis, lakeshore residents resisted TB better than people who lived elsewhere.
“It appeared that this microorganism living in the soil had powerful immune-regulating properties that were somehow making the vaccines work better,” he said.
Researchers tried using it as an immune-boosting adjunct to various vaccines, with limited success. But one trial in lung cancer patients yielded a curious result: While those injected didn’t live longer, their mood improved.
Lowry set out to find out why.
In April 2007, he published a groundbreaking study showing that when a preparation of M. vaccae was injected into mice, it activated brain cells that produce the feel-good chemical serotonin and altered the animals’ behavior in a way similar to that of antidepressants.
His peers were skeptical. “Some people commented that it must have been an April Fool’s joke,” he recalls.
But since then, he’s published an array of studies adding weight to the notion that good bacteria can be good for the mood.
One showed that children raised in a rural environment, surrounded by animals and bacteria-laden dust, grow up to have more stress-resilient immune systems and may be at lower risk of mental illness than pet-free city dwellers.
“It has already been very well documented that exposure to pets and rural environments during development is beneficial in terms of reducing risk of asthma and allergies later in life," said Lowry. "This study showed for the first time that these exposures are likely to be important for mental health.”
It’s exciting to see so many people interested in our relationship with the microbial world.” –Christopher Lowry
Another study showed that injections of M. vaccae prior to a stressful event could prevent a “PTSD-like” syndrome, fending off stress-induced colitis and making them act less anxious and fearful when stressed again later. Another found that M. vaccae has a long-lasting anti-inflammatory effect on the brain. That’s important, because brain inflammation impacts mood-regulating brain chemicals.
While more research is needed, some evidence already suggests that various other strains of bacteria—even in the form of oral probiotics—have anti-inflammatory effects and may hold potential for alleviating anxiety in humans.
Lowry is now collaborating with the Department of Veterans Affairs on a clinical trial looking at whether Lactobacillus reuteri can improve physiological and psychological responses to stressful situations in veterans with PTSD.
Meanwhile, he continues to study M. vaccae, in hopes that someday an M. vaccae-based “stress shot” could be given to soldiers or first responders to make their brains and bodies more resilient.
At home, he makes a point of exposing his own children to a healthy dose of dirt, via a front yard vegetable garden and frequent camping trips. He encourages his friends and colleagues to do the same. Only now, they’re not so skeptical.
“This idea went from being this novel, turn-your-world upside down concept to something that doesn’t even surprise people anymore,” he says. “It’s exciting to see so many people interested in our relationship with the microbial world.”