Immunity helps kids who romp in the mud and eat food that has fallen on the floor could protect them against maladies and infections later in life, a US study showed Wednesday.
"Our research suggests that ultra-clean, ultra-hygienic environments early in life may contribute to higher levels of inflammation as an adult, which in turn increases risks for a wide range of diseases," including cardiovascular disease, Thomas McDade, lead author of the study, said.
Researchers at Northwestern University in the state of Illinois looked at data from a study in the Philippines, which followed participants from birth to 22 years of age.
The data were compiled by tracking children born in the 1980s to 3,327 Filipino mothers.
Researchers visited the children every two months for the first two years of their lives and then spaced out the visits to every four or five years until the kids reached their 20s.
Among items that the researchers assessed were the hygiene of the children's household environment, "whether domestic animals such as pigs and dogs roamed freely", and their families' socioeconomic resources.
Blood tests taken when the study participants reached adulthood showed that although Filipinos suffer far more infectious diseases as infants and toddlers than their American counterparts, their level of C-reactive protein (CRP) when they reached adulthood was at least 80 percent lower than in Americans.
Filipinos in their early 20s had average CRP concentrations of 0.2 milligrams per liter, while Americans in the same age group had blood concentrations of the protein of 1-1.5 milligrams per liter.
"CRP concentrations are incredibly low in Filipinos compared to people in the United States and that was counter to what a lot of people would have anticipated because we know that Filipinos have higher exposure to infectious diseases," McDade told AFP.
One finding of the study published in the online edition of the Proceedings of the Royal Society was that adults with high CRP levels -- indicating more inflammation -- were exposed to less animal feces in the home as kids.
But that should not serve as an impetus to rush out and buy a pig to have running around the home, said McDade -- adding that Americans' obsession with hygiene would probably rule that out anyway.
Rather, he said, the message to take home from the study is the importance of being exposed early in life to common microbes and bacteria.
"These bacteria and microbes may never result in outright clinical disease but they do play an important role in promoting the development of regulatory networks," said McDade, who is an associate professor of anthropology at Northwestern and a fellow at the university's institute for policy research.
To explain the importance of exposure to such microbes, McDade, who has a two-and-a-half-year-old son, likened immune system development to the way Americans promote brain development in infants and toddlers by exposing them to "all sorts of cognitive and social stimuli."
"There's rapid brain growth early in life and there are lots of neurological connections being formed, and you need to engage with your environment in order to promote those connections," he said.
"The immune system also needs engagement with its environment to drive its development, and without that environmental input, we're depriving it of a necessary source of information that it needs to promote its development," said McDade.
And with his own child, McDade said he ignores the two-second rule when food drops on the floor.
"I don't hesitate - I tell him to pick it up and eat it," he said.