In contradiction to what your mom and grandmother and untold others told you as a child, playing in the dirt and not scrubbing every last drop of grime out of your hands may make you healthier. As NPR’s Shots blog says, it’s been known for some time that “people who grow up on farms are less likely to have ailments related to the immune system than people who grow up in cities” — less likely, that is, to have ailments including asthma, allergies, inflammatory bowel disease and multiple sclerosis. Scientists have now found more evidence for the “hygiene hypothesis,” according to which those exposed in early life to more microbes — from other children, from animals — end up with immune systems that are better able to tolerate the irritants that cause asthma and are, therefore, healthier in the long run.
Microbes in the Gut Can Be Good
A just-published study in Science has found that, when one has microbes in one’s gut in the early stages of life, a certain, rare part of the immune system – invariant natural killer T cells (iNKT) — are in retreat. Without the microbes, “the immune cells go crazy in the lungs and intestines [the colon, in particular], increasing the risk of asthma and colitis,” as NPR puts it.
Richard Blumberg, the chief of gastroenterology at Brigham and Woman’s Hospital in Boston, and other scientists made these findings about microbes and immune cells in mice who were raised in entirely germ-free environments in a lab. The researchers were intrigued to discover that “the immune response in the super-clean mouse innards looked very similar to what happens in diseases like asthma.” So, as NPR continues, the scientists exposed pregnant germ-free mice to microbes the day before they gave birth. The baby mice were found to have fewer iNKT cells in their guts in their early life.
The iNKT cells seem to be crucial to understanding the mice’s immune responses: Genetically altered mice who were reared in a germ-free environment still do not get colitis.
Study co-author Dennis Kasper, director of the Channing Laboratory at Brigham and Women’s Hospital, says that scientists now have to pinpoint which microbes out of the 500 to 1,000 species in the intestine control immune cells.
What This Study Tells Us About the Hygiene Hypothesis
As humans are not mice, the study’s results may only extend so far. But Blumberg’s and Kasper’s research certainly lends weight to the hygiene hypothesis and could contribute to recommendations about the early years of child rearing. Other studies, notes NPR, have connected antibiotic use early in life to immune-based problems like asthma and food allergies; there is also “even some evidence that women might have more autoimmune diseases than men because they’re kept cleaner than boys as children.” Also intriguing is that such auto-immune diseases are more common in people in developed countries, and in those who move to these from developing regions.
Certainly the news that exposure to some microbes in early childhood might be helpful — beneficial — for lifelong health would have an effect on the industry that has grown around children’s health, all those anti-bacterial soaps and products and even the banishment of sandboxes from playgrounds. Far from being “next to godliness,” cleanliness might only be a harbinger of an asthmatic, food-allergenic individual.
Do you think the hygiene hypothesis is accurate?
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