Allergy research giving weight to hygiene theory
By Rob Stein
THE WASHINGTON POST
March 4, 2008

First, asthma cases shot up, along with hay fever and other common
allergic reactions, such as eczema. Then pediatricians started seeing
more children with food allergies. Now experts are increasingly
convinced that a suspected jump in lupus, multiple sclerosis and other
afflictions caused by misfiring immune systems is real.

Although the data are stronger for some diseases than others, and part
of the increase may reflect better diagnoses, experts estimate that many
allergies and immune-system diseases have doubled, tripled or even
quadrupled in the past few decades, depending on the ailment and the
country. Some studies now indicate that more than half of the U.S.
population has at least one allergy.

The cause remains the focus of intense debate and study, but some
researchers suspect the concurrent trends all may have a common
explanation rooted in aspects of modern living ? including the ?hygiene
hypothesis? that blames growing up in increasingly sterile homes,
changes in diet, air pollution, and possibly even obesity and
increasingly sedentary lifestyles.

"We have dramatically changed our lives in the last 50 years," said
Fernando Martinez, who studies allergies at the University of Arizona.
"We are exposed to more products. We have people with different
backgrounds being exposed to different environments. We have made our
lives more antiseptic, especially early in life. Our immune systems may
grow differently as a result. And we may be paying a price for that."

Along with a flurry of research to confirm and explain the trends,
scientists have also begun testing possible remedies. Some are feeding
high-risk children gradually larger amounts of allergy-inducing foods,
hoping to train the immune system not to overreact. Others are testing
benign bacteria or parts of bacteria. Still others have patients with
MS, colitis and related ailments swallow harmless parasitic worms to try
to calm their bodies' misdirected defenses.

"If you look at the incidence of these diseases, a lot of them began to
emerge and become much more common after parasitic worm diseases were
eliminated from our environment," said Robert Summers of the University
of Iowa, who is experimenting with whipworms. "We believe they have a
profound symbiotic effect on developing and maintaining the immune
system."

Although hay fever, eczema, asthma and food allergies seem quite
different, they are all "allergic diseases" because they are caused by
the immune system responding to substances that are ordinarily benign,
such as pollen or peanuts. Autoimmune diseases also result from the
body's defense mechanisms malfunctioning. But in these diseases, which
include lupus, MS, Type 1 diabetes and inflammatory bowel disease, the
immune system attacks parts of the body such as nerves, the pancreas or
digestive tract.

"Overall, there is very little doubt that we have seen significant
increases," said Syed Hasan Arshad of the David Hide Asthma and Allergy
Research Centre in England, who focuses on food allergies. "You can call
it an epidemic. We're talking about millions of people and huge
implications, both for health costs and quality of life. People miss
work. Severe asthma can kill. Peanut allergies can kill. It does have
huge implications all around. If it keeps increasing, where will it
end?"

One reason that many researchers suspect something about modern living
is to blame is that the increases show up largely in highly developed
countries in Europe, North America and elsewhere, and have only started
to rise in other countries as they have become more developed.

"It's striking," said William Cookson of the Imperial College in London.

The leading theory holds that as modern medicine beats back bacterial,
viral and parasitic diseases, immune systems may fail to learn how to
differentiate between real threats and benign invaders, such as ragweed
pollen or food. Or perhaps because they are not busy fighting real
threats, they overreact or even turn on the body's own tissues.

"Our immune systems are much less busy," said Jean-Francois Bach of the
French Academy of Sciences, "and so have much more strong responses to
much weaker stimuli, triggering allergies and autoimmune diseases."

Several lines of evidence support the theory. Children raised with pets
or older siblings are less likely to develop allergies, possibly because
they are exposed to more microbes. But perhaps the strongest evidence
comes from studies comparing thousands of people who grew up on farms in
Europe with those who lived in less-rural settings. Those reared on
farms were one-tenth as likely to develop diseases such as asthma and
hay fever.

"The data are very strong," said Erika von Mutius of Ludwig-Maximilians
University in Munich. "If kids have all sorts of exposures on the farm
by being in the stables a lot, close to the animals and the grasses, and
drinking cow's milk from their own farm, that seems to confer protection."

While the evidence for the hygiene theory is accumulating, some say it
remains far from proven.

"That theory is so full of holes that it's clearly not the whole story,"
said Robert Wood of the Johns Hopkins School of Medicine.

It does not explain, for example, the rise in asthma, since that disease
occurs much more commonly in poor, inner-city areas where children are
exposed to more cockroaches and rodents that may trigger it, Wood and
others said.

Several alternative theories have been presented. Some researchers blame
exposure to fine particles in air pollution, which may give the immune
system more of a hair trigger, especially in genetically predisposed
individuals. Others say obesity and a sedentary lifestyle may play a
role. Still others wonder whether eating more processed food or foods
processed in different ways, or changes in the balance of certain
vitamins that can affect the immune system, such as vitamins C and E
and fish oil, are a factor.

But many researchers believe the hygiene hypothesis is the strongest.

Some have begun to try to identify specific genes that may be involved,
as well as specific components of bacteria or other pathogens that might
be used to train immune systems to respond appropriately.

"If we could mimic what is happening in these farm environments," von
Mutius said, "we could protect children and prevent asthma, allergies
and other diseases."

... Nickel: Once good for getting the wrong number with.
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