J.Lekavicius/ShutterstockYes, you read that right: Getting dirty may reduce your risk of depression. But before you start rolling in the mud or even worse, eating it, let’s take a step back.
The hygiene hypothesis has been bandied about for ages. In a nutshell, it suggests that we are too clean, which is why we get sick. Early childhood is the time when we should be exposed to all sorts of germs that will educate our immune system. When this doesn’t occur (because of our overly sanitized environments), the immune system doesn’t learn to recognize friend from foe and then tends to overreact to perceived threats, upping our risk for many ailments, from allergies to depression.
“Kids who play in the sandbox are exposed to a wide variety of germs, which in turn programs their young immune systems,” explains Nigma Talib, ND, a naturopathic doctor with clinics in London and New York, and the author of Younger Skin Starts in the Gut: 4-Week Program to Identify and Eliminate Your Skin-Aging Triggers – Gluten, Wine, Dairy, and Sugar.
Enter the microbiome—the name given to the microbe (bacteria) population living in our guts. Science is increasingly uncovering its powerful role in influencing immune function and chemical signaling in the brain, to the point that it’s been dubbed “the second brain.” “When you are anxious, your stomach may act up, and this is because we have more serotonin receptors in the gut than in the brain,” Dr. Talib explains. (Serotonin is the same feel-good brain chemical that is targeted by antidepressants such as Prozac). “When the bacteria in your gut is out of whack, serotonin receptors don’t function as well.”
Anatomy Insider/ShutterstockOf course, the multi-million dollar question, which can’t be answered definitely yet, is whether increasing exposure to bacteria in dirt offsets this risk.
The Down and Dirty Depression Cure?
A 2007 study in Neuroscience found that when mice were injected with a bacteria found in dirt, Mycobacterium vaccae, it activated a particular group of brain neurons that produce serotonin—just like an antidepressant does.
“There is pretty strong evidence that microbes are involved in depression,” adds B. Brett Finlay, PhD, a professor of microbiology at the University of British Columbia and author of Let Them Eat Dirt.
In fact, one study found that a single course of antibiotics boosts the risk of depression by around 25 percent, and the more antibiotics a person takes, the greater this risk becomes. That’s because antibiotics kill bacteria, and it’s possible that the very action that renders them effective against infection disrupts gut bacteria and increases depression risk. The findings appear in the Journal of Clinical Psychiatry.
“There is more and more supporting evidence that the gut-brain axis works both ways and can affect depression and anxiety,” Dr. Finlay says.
It’s true that there are many different factors that can lead to depression. “This is one potential mechanism,” says Emeran A. Mayer, MD, PhD , a gastroenterologist and neuroscientist at the University of California-Los Angeles and author of The Mind-Gut Connection. “If you grow up in an environment where you are exposed to a lot of environmental microbes, it is protective against a lot of chronic disease… possibly depression for a subset of people.”
But as tempting as it sounds from a health perspective, you should not go scoop dirt out of the yard and eat it. “You can catch a lot of bacteria and parasites that are not healthy if you eat dirt,” Dr. Talib says. There may be a role for probiotics, a.k.a “good” bacteria, however. “Probiotics do keep the bad guys in check,” she says. “Eating a wide variety of superfoods such as vegetables and fermented foods such as sauerkraut and pickles can reset the balance.”
marekuliasz/ShutterstockIn this case, they are called “psychobiotics,” Dr. Mayer adds. “Psychobiotics are certain probiotics can attenuate depression-like behavior.”
Unfortunately, Finlay says, while “there may be a day when research identifies microbes with specific functions and we can say that these gut bugs lead to depression and these don’t,” at this point there aren’t even one or even two specific probiotic strains that we can say will definitively reduce depression risk.
Until then, we can say definitively that diet—including these foods that fight depression also affects microbes, and exercise is known to boost mood, so those are good ways to ward off the blues—no rolling in the dirt required.