Hygiene Hypothesis: Are We Too Clean For Our Own Good?

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Hygiene Hypothesis: Are We Too " Clean " for Our Own Good?

 

ORIGINAL URL: http://healthlink.mcw.edu/article/1031002421.html

 

Increased hygiene and a lack of exposure to various microorganisms

may be affecting the immune systems of many populations -

particularly in highly developed countries like the US - to the

degree that individuals are losing their bodily ability to fight off

certain diseases.

 

That's the essence of the " hygiene hypothesis, " a fairly new school

of thought that argues that rising incidence of asthma, inflammatory

bowel disease, multiple sclerosis and perhaps several other diseases

may be, at least in part, the result of lifestyle and environmental

changes that have made us too " clean " for our own good.

 

" Medicine has a lot of history behind it related to why certain

diseases are so widespread and certain diseases are not widespread, "

said Subra Kugathasan, MD, Medical College of Wisconsin Associate

Professor of Pediatrics (Gastroenterology), who has made a study of

developments in hygiene hypothesis research.

 

" The immune system is there for a reason, said Dr. Kugathasan. " It's

there to recognize 'the bad guys.' The immune system allows your body

to kill those bad guys and allows you to survive. In order to harden

the immune system, the immune system requests some kind of stimuli

all the time. "

 

" The hygiene hypothesis suggests that the more hygienic one becomes,

the more susceptible one is to various autoimmune diseases. The

autoimmune diseases, the diseases that result from all the activation

of your immune system, are increasing. The hygiene hypothesis - and

we don't yet have a proof of it - acknowledges that the maturation of

the immune system needs some kind of hardening, some kind of

resistance. Put another way, you cannot really build up good muscles

without doing exercise. "

 

From Pet Dander to Pig Worms

The common belief that has driven medicine, as well as public

perception and hygiene practices, is that when we get sick it is

because of something we ate, or inhaled, or were exposed to in other

ways. The hygiene hypothesis points in a different direction,

proposing that in many diseases it is a lack of exposure to the " bad

guys " that causes harm.

 

While the evidence was by no means clear-cut, one study indicated

that in some cases contact with certain pet dander in the home

actually decreases a child's risk of wheezing from asthma later in

life. Other studies show that children who lived on farms when they

were very young have reduced incidence of asthma, which has led

several researchers to conclude that organisms in cattle dust and

manure may be the stimuli that their immune systems needed to fight

off asthma.

 

In another study, conducted by University of Iowa Division of

Gastroenterology director Dr. Joel Weinstock, intestinal worms were

shown to have a very dramatic effect on mice in offering protection

from inflammatory bowel disease. This was followed up using whipworms

from pigs, Trichura suis, in a small number of humans. The worms were

selected because they are " safe, " as many pig farmers come in contact

with them every day, they do not enter the human bloodstream, and

they cannot live in the human intestine for more than a week.

 

All of the six patients who were given the worm treatment for their

bowel disease eventually went from chronic illness to complete

remission with no diarrhea, no abdominal pain and no joint problems.

In very general terms, this small-scale test of the hygiene

hypothesis worked because microorganisms from the worms positively

affect the body's immune response to bacteria and viruses.

 

" Think about countries in Africa like Gambia, a country that has been

studied very well, " said Dr. Kugathasan. " Ninety to ninety-nine

percent of people in Gambia have intestinal worms at some point in

their lives. But the chronic immune diseases like asthma, Crohn's

disease, or multiple sclerosis are not heard of, never even mentioned

in their life. They don't know anything about such diseases in those

countries. While one may argue that maybe their population is

genetically not predisposed to these diseases, other factors appear

to be in play. "

 

" What has happened now, with globalization and human migration,

people move to areas that are very, very clean. Within one generation

we have moved into a different environment. What we have been finding

out is that in the second generation of Asian, Latin American and

African children, where the first generation had been exposed to

those kinds of parasites and early childhood infections, the second

generation that has moved to 'cleaner' countries has not been

exposed. The incidence of Crohn's disease, multiple sclerosis, and

chronic asthma is as common in the second generation from the third

world as in those with European or North American backgrounds, and in

some cases even higher. "

 

Playing in the Dirt

Dr. Kugathasan and others interested in hygiene hypothesis have not

proposed that " playing in the dirt, " or making society less hygienic

in general, are useful goals in medicine. But they do propose that

taking the impact of reduced immunological strength into account for

certain diseases could be beneficial.

 

For example, researchers who are looking into the impact of

microorganisms produced by cattle on asthma in children maintain that

the more they learn about how cattle exposure relates to asthma, the

closer they will come to developing an effective preventive

treatment.

 

" Over the years, what's happened with modern medicine is that we have

become more aware of the disease process, so we are avoiding diseases

by learning more about how they spread, " said Dr. Kugathasan. " We are

becoming much cleaner and learning how to prevent many diseases by

immunization. And we are isolating ourselves by not going into

epidemic areas. Now we don't even allow kids to play in the yard

barefoot. Children playing in the dirt barefoot are exposed to a lot

of microorganisms and worms and everything else, and that's not

happening the way it used to. "

 

" So the hygiene hypothesis doesn't only apply to Crohn's disease and

inflammatory bowel disease, " Dr. Kugathasan says. " It applies to many

other conditions. This doesn't mean children should roll around in

the dirt or necessarily change medical practice in the US. But to

keep the immune system working properly, you need controlled stimulus

or else it doesn't know how to recognize the bad guys. Treatment is

meant to suppress the system, while the hygiene hypothesis suggests

that it doesn't always hurt in the long run to give stimulus the

other way around. "

 

It's important that a child go through normal childhood illness, for

example, notes Dr. Kugathasan. " When we visit the doctor to suppress

a lot of things like colds, rather than, in effect, letting nature

run its course, we're making immediate treatment the priority rather

than long-term prevention, using the analogy of immunological 'muscle-

building.' We know that antibiotics wipe out normal cells, too, but

you don't want to destroy what medical science has accomplished.

Maybe there's no going back, but it's important that we take what the

hygiene hypothesis is telling us into account when treating our

children. "

 

Dan Ullrich

HealthLink Contributing Writer

 

 

24 September 2004

Last updated 24 September 2004

 

 

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Copyright 2003 Medical College of Wisconsin