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Thomas McDade

Chelsea R. Robbins/MEDILL

Northwestern University anthropologist Thomas McDade said parents may want to reconsider their fight to keep their kids germ free.


Germ play may prevent diseases in adulthood

by Chelsea R. Robbins
Jan 26, 2010


These days, many parents sterilize their children’s toys in bleach solutions and scrub their hands with antibacterial soap after a frolic in the sandbox.

With contagious illnesses such as swine flu spreading germs at schools and playgroups, moms and dads are eager to keep their little ones germ free.

But maybe Americans should think again. A recent study led by Northwestern University suggests that children’s exposure to everyday germs may prevent age-related illnesses such as cardiovascular disease later in life.

“In the U.S. we have this sort of hyper-sanitary culture, hyper-hygienic environment, with antibacterial soaps everywhere and cleaning products. And we might want to reconsider the application of some of those products,” said Northwestern University anthropologist Thomas McDade, lead author of the recently-published study.

“Now for the first time in the history of our species, our bodies are being deprived of exposure to those everyday germs because we live in such a sanitary environment,” McDade said.

McDade’s study marks the first look at how microbial exposures early in life impact inflammatory processes associated with adult diseases.

The researchers found that kids exposed to higher levels of infectious diseases or living in less sanitary environments in areas of the Philippines that they studied had higher levels of immunity. The immunity is related to a single protein that, in turn, may be linked to a lower risk of cardiovascular disease later in life.

McDade said exposure to common everyday bacteria early in life helps build up immunity and promotes the regulation of inflammation throughout childhood, adolescence, young adulthood and later in life.

“Think about the immune system as a system that needs information from the environment to guide its development and function, and if you live in a rich microbial environment, you get exposed to lots of germs and that helps your immune system develop,” McDade said.

The key player is C-reactive protein (CRP) found in the blood. CRP levels rise in response to inflammation in the body. But, in the presence of a strong immune system, CRP levels are relatively low. In high levels, the protein has been related to a greater risk for cardiovascular disease, according to McDade.

An increased exposure to everyday germs may help build up a child’s immune system, decreasing CRP levels and lessening the risk for cardiovascular disease later in life.

Previously, CRP levels were looked upon as a measure of infection because they are part of innate human immune defenses. But virtually all of the research done on CRP production has been conducted in affluent Western populations where the rates of cardiovascular disease were relatively high and the levels of infectious diseases low.

McDade’s research followed nearly 1,500 Filipinos from Cebu City, from birth to 22 years old, in order to understand the long-term effects of early environments on CRP production in adulthood.

“In the past few years a lot of physicians have started to include a CRP test in addition to lipids and looking at blood pressure and other standard clinical indicators for risk of heart attack,” McDade said.

“In the Philippines, we were able to reach back in time and bridge into the next generation,” said Dr. Julienne Rutherford, a co-author of the study, anthropologist and assistant professor in the College of Dentistry at the University of Illinois at Chicago.

“As a biological anthropologist, I’m particularly interested in human variation and how culture and ecology can shape human physiological systems,” McDade said. “So we wanted to do a study on CRP in a different setting than the U.S.”

Blood tests showed that CRP levels in Filipino participants were dramatically lower than average CRP levels in the U.S. McDade said the Filipinos had a CRP concentration of about 0.2 milligrams per liter compared to American’s concentration of about 1 milligram per liter.

The researchers collected their data from a study that began in the early 1980s with more than 3,000 Filipino participants whose mothers were in their third trimester of pregnancy.

Researchers followed the infants from birth into their early 20s, looking at the quality of the children’s environments, their growth, whether they were breast-fed and their levels of exposure to infectious diseases. The study looked at that information in relation to their health in young adulthood.

Over time, participants dropped out of the study and reached the study group size of  about 1,500.

The study analyzed Filipinos from all over Cebu City, including metropolitan, suburban and rural areas, but location made no difference on CRP levels.

“I was a little surprised by that,” McDade said. “But it just wasn’t there.”

His study, “Early Origins of Inflammation: Microbial Exposures in Infancy Predict Lower Levels of C-reactive Protein in Adulthood,” was recently published in the journal Proceedings of the Royal Society B: Biological Sciences.

In addition to McDade and Rutherford, co-authors of the report included nutritionist Linda Adair of University of North Carolina and anthropolist Christopher Kuzawa, also of Northwestern.

“So how do you get exposure, preserve exposure, to the positive germs that may have some beneficial effects for you developmentally while avoiding exposure to the germs that might lead to something like H1N1 or another infectious disease that could kill you?” McDade asked.

“It’s really more about maintaining a balance,” Rutherford said.