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

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

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


    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."

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    Preventing food allergies in children - a change of strategy?

    Published: Wednesday, 17-Dec-2008

    According to the Centers for Disease Control and Prevention (CDC) in the United States in 2007 around 3 million children under 18 had food allergies - a rise of 18% since 1997.
    The CDC says in 2006 about 6.8 million children suffered from some sort of allergy and for some reason which remains unclear there are a growing number of children with allergies to foods such as peanuts, eggs and fish and these affected children are two to four times as likely to have related conditions such as asthma or other allergies.

    Experts say while improvements in diagnosis could partly explain the increase, allergies do appear to be more common at present than they were a generation ago.

    A suspected culprit in the increase in both food and environmental allergies is thought to be the 'hygiene hypothesis' where the current vogue for scrupulous cleanliness removes the immune system benefits from early exposure to bacteria.

    Some experts suggest that the more hygienic the environment, the more allergies there will be while others believe that a lack of exposure to specific foods in infancy may result in allergies to those foods later on.

    Once an allergy develops the only option is to manage the symptoms and at present how to prevent allergies from developing in the first place, remains a dilemma.

    Research suggests that the causes of allergies are a complex mixture of genetics and environment but a new study of 8,600 Jewish children in the United Kingdom and Israel may ultimately provide some insight.

    The British and Israeli researchers found that the early consumption of peanuts in infancy was linked with a low prevalence of peanut allergy.

    The researchers say despite guidelines recommending avoidance of peanuts during infancy in the UK, Australia, and, until recently, North America, peanut allergy continues to increase in these countries.

    They set out to determine the prevalence of peanut allergy among Israeli and UK Jewish children and the relationship with peanut consumption by mothers and children.

    The study involved 5,171 schoolchildren in the UK and 5,615 in Israel and included a questionnaire on peanut consumption and weaning involving 77 infants in the UK and 99 in Israel.

    The researchers found that the UK Jewish children had 10 times more peanut allergies than the Israeli infants and the difference came down to the fact that the Israeli infants consume peanut in high quantities in the first year of life, whereas UK infants avoid peanuts.

    They say their results raise the question of whether early introduction of peanut during infancy, rather than avoidance, will prevent the development of peanut allergies and that with food allergies, there might be a benefit from early exposure.

    A proposed clinical trial by researchers in the UK is currently recruiting 480 children ages 4 months to 10 months who will be randomly assigned to consume or avoid peanuts but these results are not expected for about five years.

    While there is at present some hope in oral immunotherapy, where gradually increasing an allergic person's exposure to offending foods, might help ward off allergies, that therapy is still to be proven.

    The American Academy of Allergy, Asthma and Immunology now recommends that vegetables, rice, meat, and fruit should be added to a child's diet between 6 months and one year so that problem foods can be easily identified.

    The Academy says thereafter a child should try milk, wheat, corn, citrus fruit, and soy and at age 2, eggs and at 3, fish and peanuts.

    Experts say children with parents who have allergies should be regarded as high risk but breastfeeding for the baby's first four to six months of life offers some protection.

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