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Sunday, April 11, 2010

It just doesn’t pay for humans to be too clean

Microbes are people, too.

Well, not exactly. But after a century or so dedicated to trying to sanitize everything we ingest, touch or sit on, researchers are coming to a new appreciation for the favors many bacteria – aka germs – do for our biological function.

It’s well established that our digestive systems falter if we don’t keep a proper balance of helpful bacteria in our gut – and a whole industry of probiotic foods and supplements has sprung up to do just that.

Researchers have concluded that the major reason humans – and most higher mammals – have an appendix is because the little cul-de-sac at the end of the intestines evolved to serve as a refuge for populations of the essential bacteria should some catastrophe wipe them out in the rest of the tract.

For more than a decade, allergists and immune-system specialists have been talking about the “hygiene hypothesis” that suggests early exposure to infectious agents, parasites and allergens helps build a healthy immune system.

Numerous studies have shown that immune problems such as asthma, hay fever and a host of other conditions related to inflammation are affected by everything from living in modern housing and day care attendance to being part of large families and living on a farm.

In one recent study, researchers at Northwestern University followed 3,000 Filipino children from a few months before birth through 22 years of age, analyzing their infection history and inflammatory response, particularly as marked by C-reactive protein. The protein increases in the blood during inflammation of the immune system and has been used as a warning sign for heart disease.

The researchers then compared the Filipinos to a group of young adults in the United States. They found that while the Filipinos suffered from far more infectious diseases as infants and children, by age 22, their levels of C-reactive protein were 80 percent less than in the American group.

“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 risk for a wide range of diseases,” said Thomas McDade, an associate professor of anthropology who led the study.

According to the World Health Organization, such autoimmune diseases as type-1 diabetes and multiple sclerosis are rare in most rural African and Asian populations, but that those rates go up when people from those populations migrate to more developed settings.

A British study published last year worked with mice and found that those with lice infestations had less hyperactive immune response than did animals without the parasites, bolstering claims that people have stronger allergic reactions in part because most of us live without such pests to desensitize us.

There’s even evidence that it isn’t wise to make our skin too clean. Studies of health care workers have found that excessive hand-washing with antimicrobial soap can actually damage the skin and make it easier for bacteria to hide and spread.

Researchers have also discovered that the germs on our hands aren’t like those on other hands – the typical human hand contains 150 species of bacteria, with only 13 percent shared by any two people.

Scientists at the University of Colorado have been using this information as a sort of germy fingerprint that could identify which person or persons had recently touched a particular object.

They’ve also noticed that the variety of bacteria found on our hands doesn’t change much even if people regularly wash them.

Lee Bowman of Scripps Howard News Service can be reached at Bowmanl@shns.com.