What Can Happen When You’re Way Too Clean

People are far cleaner than their ancestors were. Thanks to better sanitation systems that remove waste and public works programs that clean water—not to mention the proliferation of soaps, cleaning agents and antimicrobial products that sterilize our environments—we’re exposed to far fewer microbes than ever before. But proponents of the so-called “hygiene hypothesis” say that being too clean changes the bacteria that live within us, making us more susceptible to allergies, asthma and other immune-related conditions.

Now, a study published in the journal Cell provides more evidence that this might be true. And it may be related to incidence of diabetes, too. The findings support the hygiene hypothesis, illustrating that the environment in which babies are raised and the microbes they’re exposed to at a very young age can make a big difference in the types of bugs they nurture in their bodies. That in turn can affect their risk of certain diseases.

Researchers led by Tommie Vatanen, from the Broad Institute of MIT and Harvard, found that the gut bugs from babies born in a rural part of Russia were significantly different from those found in infants born just across the border in more urban settings in Finland and Estonia. Among the Russian newborns, the dominant byproducts from bacteria were from E. coli or the bifidobacterium species, while newborns in Finland showed more products from Bacteroides species. The Estonian infants showed levels in between the two; in that region, economic development is gradually shifting from an agrarian lifestyle to a more urban one.

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Not only did the researchers document different types of bacteria in the different populations, but they also found that these correlated with different levels of type 1 diabetes. Rates of the disease were higher among the Finnish babies and lower among those born in Russia. Even after the scientists adjusted for factors that can influence the colonization of gut bugs, such as diet, environment and breastfeeding, which can introduce microbes from the mother to the baby, the difference in microbes between the geographical regions remained strong.

“We know the Russian kids lived near or on farms and clearly had exposure to a broad spectrum of microbes in the soil as well as from animals,” says Ramnik Xavier, senior author of the study from the Broad Institute. “The Finns were living in an ultra-clean environment and spent most of their early live in concrete towers that didn’t given them the same exposure.”

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In other studies, exposure to the bacterial species found in soil and rural environments was linked to higher production of fatty acids that can fight pathogens responsible for respiratory infections and affect metabolism. Having different colonies of bacteria can therefore result in different ways to educate the immune system, which can give children more or less protection against things like allergies and metabolic disorders like diabetes.

“Everyone is going to try to come up with what is the best cocktail of probiotics to give to the Finnish kids to delay the onset of type 1 diabetes or prevent it in kids who are at high risk,” says Vatenan. “But to do that, we still need more information.” He and his colleagues are already collecting that data; they’re studying the microbes in the guts of the rare people who seem to be protected against developing type 1 diabetes, for example, as well as those who develop the disease more slowly, to see if their bacterial makeup is different in any way. That could fuel studies that try to pinpoint exactly which types and doses of probiotic cocktails may help to control or even prevent conditions like diabetes and allergies.