Are kids too clean for their own good?

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© Lou Cypher/Corbis

Raising children in an über-hygienic atmosphere may inhibit immune system development key to fighting infection and disease later in life, according to a new study from researchers at Northwestern University. Researchers followed a group of more than 3,000 Filipino children from their mother’s third trimester of pregnancy through 22 years of age, and analyzed the levels of C-reactive protein (CRP), which increases in the blood during immune system inflammation. In the past, this protein has been analyzed as a way to predict conditions such as heart disease. In this latest study, published online in the journal Proceedings of the Royal Society B: Biological Sciences, researchers found that, while Filipinos suffered from far more infectious diseases and illness as infants and children, by young adulthood they had dramatically lower levels—80% lower—of CRP compared with young adults in the U.S.

While the presence of CRP has been studied in the U.S. and Europe, researchers were eager to analyze levels of the protein in a population with both higher levels of childhood infectious disease and lower levels of obesity and heart disease than the U.S. They found that, indeed, children in the study had far higher levels of illness growing up than U.S. children, but that, by young adulthood presence of CRP was dramatically different from that of American children. By their early 20s, people from the Philippines had average CRP blood concentrations of .2 milligrams per liter, a fraction of the average of 1 to 1.5 milligrams per liter among Americans in the same age group.

The findings contribute to a growing body of literature exploring the potentially detrimental health effects of an overly hygienic upbringing. Until relatively recently humans did not live in such sterile environments, study authors point out, and while many of our societal advances have been responsible for great breakthroughs in health and medicine, so completely limiting early exposure to microbes—or more broadly, dirt and grime—may be interrupting the priming process that our immune systems have gone through for all of evolutionary history. That is, perhaps, over the years, we’ve become too clean for our own good.