Sunday, July 31, 2011

America's Asthma and Allergy Epidemic

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Back in 2008 I attended a symposium at the NYU School of Medicine where I work. The symposium was about Inflammation and Host Defense. There were many good talks, including one on how the immune sysytem itself can participate in the development of cancer, of how inflammation interacts with metabolism, and how inflammatory bowel disease develops depending on a complex interaction between the immune system and the natural bacteria in our gut.

But one talk in particular caught my attention in the context of the modern epidemic of allergies and asthma. And it came at a particularly important time because certain talk show hosts were spreading misinformation about asthma. Radio talk show host Michael Savage insensitivity attacked children with asthma:

"[W]hy was there an asthma epidemic amongst minority children? Because I'll tell you why: The children got extra welfare if they were disabled, and they got extra help in school. It was a money racket. Everyone went in and was told [fake cough], 'When the nurse looks at you, you go [fake cough], "I don't know, the dust got me." ' See, everyone had asthma from the minority community."

This is just stupid. Really literally stupid, as well as mean-spirited. There is real science out there regarding the asthma epidemic and related allergy epidemic and these ignorant statements by the likes of Michael Savage and I hope he chooses to get better informed. I want to counter the misinformation about asthma that talk shows have been spreading.

First off, allergies and asthma are both, in essence, an over-reaction by the body's immune system to harmless molecules in the environment. The over-reaction is such that it can actually harm a person. A related syndrome is auto-immunity, where the body's immune system, possibly triggered by an actual infection, starts to attack one's own body. The immune system is extremely complicated, with many different types of cells and chemical messages that coordinate the immune response. The exact balance of all these cells and messages are what determine how well your body responds to stresses like infection. For example, two different responses to the HIV virus can determine the difference between rapid onset of AIDS or longer life with the infection. If I am remembering this correctly, if the body produces predominantly one type of cell (Th1 T-cells) in response to the virus, you are more likely to have rapid onset AIDS and a poorer prognosis. If the body produces predominantly adifferent kind of cell (Th2 T-cells) you are better able to control the infection and have a better prognosis. It is unclear why some people's immune system react to HIV with a Th1 response and others with a Th2 response, but genetics probably plays a part.

A similar situation occurs with asthma, allergy and auto-immunity. The precise balance of what chemical messengers and what immune cells that are produced by the body in response to the environment determines if the body doesn't react, reacts appropriately, or damages itself by over-reacting.

At the 10th annual Skirball Symposium at the NYU medical center in 2008, among many interesting talks, was one by Richard Locksley on asthma and allergy which has some very interesting implications. And shows how unhelpful and unscientific Michael Savage's attacks on victims of asthma is.

Let's begin with some numbers from the talk. Between 1980 and 1994, asthma rates went up 75%. I will add (from here) that over the same period the rate for children under the age of five increased more than 160%. This is one of those epidemiological red flags that indicates SOMETHING has changed rapidly that is affecting health. Too often these epidemiological red flags are sadly ignored, yet they can teach us so much. And the cost of this is some $12 billion a year in healthcare costs (other estimates are as high as $18 billion per year in direct and indirect costs). Asthma accounts for one-quarter of all emergency room visits in the United States, which accounts for part of the high cost to society. These are the real numbers behind what Michael Savage thinks is a scam, yet in reality is a real healthcare issue with a very real cost. And the cost is beyond the economic costs. Children 5-17 years of age missed 14.7 million school days due to asthma in 2002. This impacts on a child's education. Asthma accounts for approximately 24.5 million missed work days for adults annually. This impacts on American productivity and thus our economy.

The impact of asthma is greater on poorer Americans (who often are also minorities) than on wealthier Americans. This may be partly due to a better ability of wealthy Americans to treat asthma because they have better access to healthcare, but it goes beyond this. From WNBC back in 2006:

High levels of pollution in the South Bronx may be related to an asthma epidemic experienced by the area's children, according to a new 5-year study released by New York University on Monday.

Researches from NYU's School of Medicine and the Wagner Graduate School analyzed data collected by children wearing special backpacks, which measured the air in their homes, neighborhoods, and their schools...

During the study, the symptoms of asthma doubled among elementary school children on days with a greater-than-average amount of traffic...

George Thurston, from the NYU School of Medicine, said the diesel soot was most associated with the worsening of the children's symptoms.

Twenty percent of children in the Bronx attend school within 500 feet of a major highway, which are typically places where pollution exceeds the acceptable levels, the report said.

Pollution seems to be part of what is causing the current asthma epidemic according to this study. And pollution is generally worse in poorer areas. From an article in The Nation:

Of course, given the deliberate placement of highways, industrial factories, airports, and other emitting infrastructure in American cities, poor youth are bombarded with a disproportionate amount of poisons. Frighteningly enough, as climate change warps the environment, these airborne toxins may strengthen, too. In a 2004 report, the American Public Health Association and researchers from Harvard University concluded that a "powerful one-two punch" of elevated pollen levels and modifications in the types of molds incited by climate change will boost the asthma rates of children in America's cities.

Pollution and mold. At the talk on asthma by Richard Locksley, he described his work identifying the cellular responses of the immune system that cause asthma. Allergies and asthma are actually related to our response to parasites like parasitic nematode worms. These worms are common parasites in the developing world and probably represented our normal state of life through most of our evolution. Our immune system evolved to deal with these parasites. There is considerable evidence that asthma and allergy (and maybe auto-immunity) are this immune response to parasites gone wrong. This can be seen clearly in the fact that the chemical messages and cells involved in responding to nematode parasites are largely the same as those involved in asthma and allergy. Furthermore, treatments that impair the immune response to these worms also inhibit asthma and allergy responses.

Dr. Locksley looked at what genes are turned on in response to the chemical messages that are shared between the immune response to parasitic worms and in asthma. Among the genes he found turned on were ones the protein chitinase. Chitinase is an enzyme that breaks down chitin, which most people know as the substance that makes up the shells of insects, crabs and lobsters. In fact, there is a syndrome among people hired in industrial crab processing plants of sudden asthma attacks on the job. Some 25% of newly hired people have this response, possibly due to the chitin they are handling. This implies that a good part of our immune response to parasites, and hence of allergy and asthma, is a reaction to chitin. Why chitin?

When I thought about it, this makes perfect sense. All around us are things encased in chitin. Parasitic worms lay eggs coated in chitin. Dust mite droppings include chitin. I suspect cockroach droppings do too (certainly cockroaches themselves are nasty little chitin critters). And fungi, including molds, contain chitin. All of these are well known to produce immune or allergic responses.

In my research (not professionl!) on black mold, which has been an ongoing problem in many buildings including the one I live in, I discovered that according to a 1999 Mayo Clinic study, nearly all chronic sinus infections (afflicting about 37 million Americans) are a result of mold. When I first saw this, my wife and I both wondered how much of those chronic sinus infections were really allergic reactions rather than actual infection. I know personally when my apartment was suffering from various leaks and had recurring mold outbreaks, I myself had recurrent chest infections. When we finally got rid of the mold, those infections disappeared. In retrospect I suspect I was reacting to the mold.

Well, mold contains chitin. Chitin is one of the main molecules that produce a strong immune response. Since nematode worm infections are not common in America, and since dust mites are ubiquitous anyway, I suspect another factor that influences the rise in asthma and allergy rates is an increase in mold in our environment. I know of no figures on whether mold is an increasing problem, but the incidences of black mold infestation, which can actually lead to buildings becoming uninhabitable, have been on the rise. I suspect aging buildings (particularly public housing) and aging pipes (which leak, as I can tell you from my own building!) will create the perfect environment for mold to grow. Global warming also, as long as moisture is present, encourage more mold growth. This sounds to me like an ideal situation for an asthma and allergy epidemic and I think it could well affect poorer neighborhoods more than wealthy neighborhoods, though it is occurring everywhere.

There is another theory that the almost OCD style cleanliness fixation America currently has (with advertisements scaring us about all that bacteria around us) is why asthma rates are increasing. This theory goes that there is a balance between bacteria and fungi in the environment. Kill off one and the other has a better chance of growing. Bacteria also break down chitin, so in another form this could be seen as a balance between bacteria and chitin. If we are so obsessed with killing of bacteria in our environment, we may be inadvertently helping the chitin world and thus exposing ourselves to more chitin.

While I DO believe many are too concerned about sterilizing our homes with bleach, I am not convinced by this. Bleach kills fungus as well so it is unclear whether we are altering that balance by bleaching every surface. But another, vaguer version of this theory is merely that by reducing the real things our immune system react to, we are increasing inappropriate responses. This also, I feel, has little factual backing. But both versions are possible. We DID evolve to be adapted to an environment full of parasites, bacteria and such. We did not evolve to be adapted to an environment that is sterile on the surface but mold-filled behind the walls and filled with air pollution.

Pollution and mold. These are likely to be responsible for a great deal of the increase in asthma and allergy rates in the US. It wouldn't explain everything necessarily. For example, how would pollen allergies fit into this? I think that is unclear right now. Pollen does not contain chitin. Possibly irritation of the lungs of any sort, like pollen grains and pollution, creates a low level immune response that generally makes one more sensitive to allergic reactions. Certainly allergies can occur to other things, like the particularly deadly peanut allergy.

It would be interesting to see WHICH KIND of pollutants trigger allergies and asthma. Soot? Nitrous compounds (which in some ways mimic some of the chemical messengers in the body)? Sulfur compounds, which acidify rain and water? It is unclear and I am unaware of any research in this area.

But what is clear is that pollution and chitin are two major factors involved in high asthma rates and possibly are involved in the INCREASING asthma rates. Better appreciation of this and practices that reduce urban pollution and deal with mold problems throughout cities could decrease asthma and allergy rates, thus saving our society money, improving productivity and reducing absence rates among kids in school.


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