About 20 miles southeast of South Bend, Indiana, straddling US highway 6, lies the farming village of Nappanee, population 6,692. The town has the distinction of being the only municipality in the United States with a name in which each letter is repeated once.
Nappanee is also known as the “southern gateway to Indiana Amish country.”
A few miles north of the city, a family we’ll call Stoltzfus (a common Amish name) runs a small dairy farm that has been in the family for many generations. A traditional Amish farm, the Stoltzfus operation is decidedly low tech: Horses, not tractors, do the heavy work, and the family feeds and milks its cows by hand. The distinctive red barn sheltering the farm animals sits right next to the farmhouse. The Stoltzfus family uses manure instead of fertilizer and never employs pesticides on its 80 acre plot.
The Stoltzfuses are typical of Amish farmers in the region in most respects, including the happy circumstance that none of the Stoltzfus children suffer from asthma.
According to research from the University of Arizona cited recently in the prestigious New England Journal of Medicine (NEJM), about 5 percent of Indiana Amish children suffer from asthma, compared with 10 percent in the general population.
None of the above.
The August 2016 NEJM article, "Innate Immunity and Asthma Risk in Amish and Hutterite Farm Children," asserts that the cause of the low asthma rates is most likely… dust.
Owing to the close proximity to farm animals and frequent contact with bacteria-rich dirt, house and barnyard dust on Amish farms is chock full of microbes and bacterial toxins called endotoxins. This rich cocktail of seemingly harmful microscopic particles is unique, even among farming communities. For example, the Arizona researchers discovered that dust in homes of Hutterites of South Dakota, a religious group similar to the Amish, lacked many of the unhygienic constituents of Amish dust.
The reason? Hutterites make extensive use of new technology, operating “industrial” farms in which animals are kept far from farmhouses. So bugs and toxins from the farm animals don’t make their way into household dust.
Coincidentally, Hutterite children suffer from Asthma at rates comparable to or even greater than the national average.
So why does “toxic dust” paradoxically protect against asthma, and what does asthma have to do with mental health?
A fast-growing body of research suggests that immune disorders such as asthma (in which the body attacks harmless particles such as pollen, triggering damaging inflammation) may be acquired in childhood when the immune system fails to get proper “exercise” by being exposed to “old friend” microbes (bacteria, viruses and parasites that have co-evolved with humans over thousands of years) that seldom cause disease, but stimulate and educate the immune system to differentiate between harmless and harmful antigen proteins.
Thus through early exposure, the “old friends” build healthy immune systems that neither overreact—with allergies and autoimmune disease (e.g. arthritis, colitis, eczema)—nor underreact, lowering resistance to infection or cancer.
As a consequence, individuals with healthy immune systems will generally have less inflammation due to allergy, autoimmune reaction, or infection.
Which brings us to mental health. Chronic inflammation has been recently implicated in a broad range of mental disorders, including depression, anxiety, bipolar disorder, OCD, and schizophrenia.
Elevated inflammatory compounds such as cytokines have been shown to trigger depression, social avoidance, and inactivity, which probably evolved as a protection against further injury or infection when our distant ancestors were sick or injured.
Research also suggests that inflammation in the central nervous can disrupt neuronal function and trigger or exacerbate mental disorders such as schizophrenia.
New hope for preventing and treating mental illness?
The links between “old friend” microbe exposure and low inflammation on the one hand and high inflammation and mental illness on the other hand raise a question: Could exposure to “old friend” microbes help prevent or treat some mental illness by developing healthier immune systems that don’t promote inflammation from allergy or autoimmune response?
Epidemiological data suggest that the answer is a firm… maybe. Here are the numbers:
None of these statistics prove conclusively that exposure to bugs prevents mental illness or that lack of such exposure promotes it. However, the numbers do suggest promising new avenues of research for prevention and treatment of a wide range mental health problems.
Near-term implications for preventing and treating mental disorders
It’s unlikely that you’ll see certified Amish dust inhalers or sprays in the supplement section of your local supermarket or pharmacy anytime soon, although physicians researching the apparent protective properties of “old friend” dust have seriously suggested nasal sprays containing the potent dust as a prophylactic measure against asthma during infancy.
But recent studies of child health in different environments hint at some relatively simple ways that infants' immune systems and future mental health might be boosted.
Exposure to dogs, cats, and mice in the first year of life seems to lower asthma risk. But there is evidence of a “critical period” for training children’s immune system, where exposure after the first year is much less effective than in infancy. Although very little research has been done on early exposure to animals and eventual development of mental disorders, the inflammation theory of psychiatric disorders suggests that there could well be some benefits of pet ownership for families with infants. Also, incidence of depression is lower in people who do not have chronic inflammatory diseases such as hay fever, asthma or eczema.
The likelihood of developing childhood asthma decreases as the number of older siblings increases, hinting that microbes brought into the home by other children could be protective for infants. Thus, only-child infants might benefit from more frequent proximity to other children, for example, in day care centers.
What about older children and adults with allergies and/or mental disorders aggravated by chronic systemic inflammation?
First, anti-inflammatory medications, such as aspirin, ibuprofen, and especially celecoxib (Celebrex) have recently been shown to reduce anxiety and depression in some patients. Coincidentally, traditional antidepressants, such as SSRI inhibitors, have also been shown to have anti-inflammatory properties. Of course any mental health benefits of taking anti-inflammatory medications must be weighed against the risks (bleeding with aspirin, gastrointestinal side effects with both aspirin and other NSAIDs).
Second, although evidence for any benefit of exposure to “old friends” after infancy is scant, fast-accumulating research in the field of biomics (on harmless microbes in the gut and on the skin) suggests alternate ways to reduce some forms of chronic inflammation and mental illness.
Imbalance of gut microbes, as with Crohn’s disease and Irritable Bowel Syndrome, is associated with higher rates of depression and anxiety, possibly due to inflammation and direct influence of “bad bugs” in the gut on mood centers in the brain. Aware of such correlations, UCLA scientists found that the brains of women who regularly consumed yogurt containing “good bugs” exhibited less stress and anxiety responses on an fMRI than brains of women who did not eat the culture-rich yogurt, suggesting that “good” bugs in the gut can be beneficial to mental health. This finding correlates with other research showing protective effects of yoghurt consumption for post partum depression in women. Another study showed that men who took probiotic pills had lower anxiety than men who did not.
Irish researchers at the University College Cork studying link between gut microbes and mental health found that fecal matter transplants from depressed and anxious humans into rats produced signs of depression and anxiety in the rodents. The researchers speculate that fecal transplants from “non-depressed” humans into depressed and anxious humans could have beneficial effects.
Summing up, our journey began with the mystery of unusually low asthma rates among the Amish, but ended, as often happens in science, in an unexpected place—with new possibilities for reducing mental illness, such as early pet exposure and day care centers for infants and consumption of microbe-laced concoctions for older children and adults.
Yes, some of these new strategies may be hard to swallow—literally and figuratively—but my gut tells me they are worth exploring further.
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