Research News

Germs at 4, Less Inflammation at 40

IPR anthropologists say playing in the dirt as kids makes chronic disease less likely later in life


Thomas McDade and Christopher Kuzawa
IPR biological anthropologists Thomas McDade and Christopher Kuzawa show how children's exposure to germs can affect inflammation and health in adulthood.

IPR biological anthropologist Thomas McDade realized early in his career that a lab was not the best place to study human development. As a young anthropologist, he traveled to the islands of Samoa, the deserts of Kenya, and the rainforests of Bolivia to understand how kids grow up around the world. It was through these experiences that he made key observations that helped set the path of his research career.

Thomas McDade
Thomas McDade

"Obviously, the way kids grow up in these places is socially, ecologically, and culturally different from the way kids grow up in the U.S., but there's more to it," McDade says. "As we develop, no matter where we are, we literally embody information from our environment."

In 2010, using data from a long-running study in Cebu, Philippines, McDade and fellow IPR biological anthropologist Christopher Kuzawa published the first-ever study showing that babies surrounded by germs grow up to have lower levels of inflammation in later life.

"Prior research had shown that being exposed to certain types of germs and parasites during early life might, somewhat paradoxically, reduce one's risk of suffering from allergy later in childhood and adulthood," Kuzawa says. "Our research in the Philippines extended this work by investigating whether inflammation—another aspect of immune function that has broad health impacts—might also be altered in response to these exposures."

A More Mindful Immune System

How does playing in the dirt as children make us healthier throughout our lives? Kuzawa and McDade say inflammation is the key.

Christopher Kuzawa
Christopher Kuzawa

Inflammation has been identified as a frequent indicator of trouble at our body's cellular level. More and more studies like McDade and Kuzawa's link inflammation in our bodies to increased risk for a whole host of diseases, from asthma to dementia. But exposure to germs, especially in early life, educates our immune system and helps it regulate inflammation more effectively.

"The developing immune system is similar to the brain," McDade says. "No one questions that a baby needs exposure to language to drive the neurological processes that underlie the development of speech. The immune system is similar; its development is driven by exposures from the environment. In this case, the key exposures are microbial. Without those exposures, it doesn't work quite right.”

McDade says poorly educated immune systems, and poor regulation of inflammation, partially explain the rising rates of celiac disease and allergies, as well as chronic diseases—or, as McDade calls them, "diseases of affluence"—that we see in the U.S., where germs are religiously scrubbed away at home and at work. Those trends don't show up elsewhere, in places like the Philippines, where children are exposed to more dirt and bacteria from birth.

 "Inflammation seems to underlie or contribute to so many diseases," McDade says. "Cardiovascular disease, diabetes, dementia, certain cancers, and even depression—basically everything that does us in as we age in the U.S. and other affluent countries has an inflammatory component. So the understanding that germ exposure has an impact on inflammation touches almost everything in our health care system."

McDade is quick to note that not all germs are beneficial for immune system development, and distinguishing between disease-causing and more run-of-the-mill microbes is key. To his dismay, some anti-vaccine advocates and others have taken his work out of context.

"The microbial exposures that help our bodies learn to regulate inflammation are typically non-infectious—they're in dirt, rotting vegetables and non-purified water systems," he says. "They have been a normal part of the human environment for millennia. These are not the microbes that cause measles or mumps or other infectious diseases."

Longer, Healthier Lives

This means that a little more exposure to germs as babies could lead to incredibly lasting and wide-ranging health improvements. With better foundations in our early years, Kuzawa says, not only could we grow up healthier and live longer, but we could also save massive amounts of money on medical care.

“It’s my hope that our research will inspire new approaches to child development designed to engage our immune systems in safe ways during early life, and help reduce some of the long-term burden of chronic disease,” Kuzawa says.

U.S. healthcare costs are astronomically high and only getting higher, and the majority of these costs stem from chronic diseases—stroke, heart disease, diabetes, cancer, to name a few. 

McDade and Kuzawa are now considering how their research can inform policy and practice.

"Maybe we can develop something analogous to a vaccine to give children a safe dose of germs at key moments of immune development in the first six months to two years of life,” McDade says.

For McDade, this work on the role of germ exposure in immunity and inflammation prevention is part of a broader goal of bringing environmental factors to the table in discussions of health and disease.

“If we really want to have an impact on improving quality of life around the world, then we need to think more broadly about how human development happens and the factors that matter to human biology,” McDade says.

McDade and Kuzawa’s work shows that we can prevent many chronic health conditions—and their accompanying drug and treatment costs. We just have to let our babies get a little dirty, or at least put down the Purell.

Thomas McDade is Carlos Montezuma Professor of Anthropology. Christopher Kuzawa is professor of anthropology. Both are IPR fellows.

This article was originally publisehd by Northwestern Now.