Asthma has become a critical health problem. In all major industrialized countries, the number of people with asthma increases each year. In the US, the prevalence of asthma has doubled in the last two decades.
Much attention has been given to the effect of environmental stressors on asthma (especially fine particulate air pollution; see Progressive Health Observer #3 "Smog, Deadlier Than Ever"). However, less attention is paid to the prevalence of allergies generally, with asthma as the most extreme form.
Allergy "attacks" are triggered by contact with an allergen. In the classic case of seasonal hay fever, the allergen is a protein from a pollen particle. Although asthma is classified as a form of allergy, attacks can be triggered not only by common allergens but by anything that irritates the lungs--especially fine particulates from fossil fuel exhaust.
Allergies and asthma, referred to as type 1 hypersensitivity, are immune responses to otherwise "innocuous" substances. Your body responds as if it were under attack. Allergy symptoms are your body's attempt to get rid of the invader.
Being allergic tends to run in families--if your parents have allergies, you're more likely to have allergies. However, you might not be allergic to the same things. What you inherit is an immune system that tends to overreact. And if you're allergic to one thing, you're more likely to be allergic to others.
This idea led Dr. Samuel Arbes and his colleagues to investigate whether the increase in asthma is from more allergens or greater sensitivity. Are more people having allergic reactions just because there's more stuff provoking them? Or are we becoming more sensitive to our environment?
SENSITIVITY RISING
The Arbes study was limited and only provides partial answers, but it strongly suggests that we are in fact becoming more allergic to our environment. The study's findings are consistent with similar studies in Japan, the United Kingdom, and Denmark.
Arbes looked at data from the two latest National Health and Nutritional Examination Surveys--referred to as NHANES II and NHANES III--conducted from 1976 to 1980 (NHANES II) and from 1988 to 1994 (NHANES III).
NHANES II and NHANES III each conducted allergy skin tests for common allergies. Only six were the same in both surveys: ragweed, rye grass, Bermuda grass, oak, cat dander, and the fungus Alternaria alternata that's common on plants and crops.
What Arbes found was that the percentage of people who reacted to at least one of these allergens doubled between NHANES II and NAHANES III. And the percentage of people who reacted to each of the individual allergens increased from a low of 2.1 times for ragweed to a high of 5.5 times for cat dander.
Change in percentage of people who react to six common allergens
................Percent who reacted in..............
Allergen.....1976-80....1988-94....Change
Ragweed.....12.5%.........26.2%.........2.1
Rye.............11.9%.........26.9%.........2.3
Oak.............5.8%..........13.2%.........2.3
Fungus........4.5%..........12.9%.........2.9
Bermuda......5.2%..........18.1%.........3.5
Cat..............3.1%..........17.0%.........5.5
There is no indication that our exposure to any of these allergens has increased. The increase can only be explained by an increase in sensitivity. The implication for asthma is that although our exposure to environmental triggers like air pollution has increased, our susceptibility has also increased.
Why have we become more sensitive?
IMMUNITY AND ALLERGY
Type 1 hypersensitivity (allergy) is an immune response. The job of the immune system is to recognize unwanted substances and organisms and prevent them from doing harm.
Antibodies are a familiar part of the immune system. They are a kind of memory of unwanted organisms. Specialized white blood cells called B cells (because they're produced in bone marrow) produce antibodies that recognize an invader like a virus. The antibody latches onto the virus and attracts macrophages (another kind of white blood cell) that destroy the virus. Antibody production is orchestrated by another kind of white blood cell: a type 1 helper T cell (produced in the thymus) also referred to as a TH1 cell.
This classic immune response is typically accompanied by inflammation. The purpose of inflammation is to mobilize the immune system's resources. When the endothelial cells that form the outer surface of a tissue sense a foreign substance, they send out chemical signals called cytokines. In sending the signal, three things happen that make up the inflammatory response: - blood flow increases to the tissue; - white blood cells are attracted to the site; and - the small blood vessels (capillaries) that supply the tissue become more permeable, permitting white blood cells to get to the tissue.
Antibodies are created from biochemicals called immunoglobulins. The three most common immunoglobulins are designated IgG, IgA, and IgM. IgG is present throughout the body and composes 75% of all immunoglobulins. IgA is in mucous membranes. IgM is in blood.
The principal antibody in type 1 hypersensitivity is IgE, a minor fraction of total immunoglobulin. Not surprisingly, it is located primarily in the tissues that come into contact with the outside--mucous membranes and skin.
When your sinuses, lungs, gut, or skin contacts an allergen, IgE acts toward the allergic protein as an antibody would toward a virus: it latches onto it and triggers an immune response by mast cells, yet another specialized white blood cell.
Mast cells are fat with histamine granules--"mast" means "well fed" in German. When triggered by IgE, mast cells degranulate, releasing histamine. This causes inflammation. Like IgE, mast cells are concentrated where your body meets the outside--mucous membranes and skin.
Just as an antibody "remembers" a virus, an allergen-specific form of IgE "remembers" that allergen. The more exposure to an allergen in the environment, the more inflammation and allergy symptoms occur. Unlike antibody-mediated reactions, IgE-mediated reactions do not involve B cells. But the process is orchestrated by a type 2 helper T cell (TH2 cell).
IgE's principal role in the normal function of the immune system is in defending against parasites. In regions where parasites like hookworm are common, blood levels of IgE are 100 times greater than in regions low in parasites. In a sense, an allergy attack happens when your immune system mistakes an allergen for a parasite.
WHY THE INCREASE IN SENSITIVITY
Two theories have been offered to explain the increase in allergic sensitivity: the hygiene hypothesis and the environmental stressor theory.
Proponents of the hygiene hypothesis originally argued that Western cultures have sanitized their environments so much that their immune systems don't develop properly. That is, early exposure to pathogens and allergens helps build immunity and low rates of allergy.
While credible research supports the theory, many critics point out significant instances where it does not hold up. For example, the higher rate of asthma among minority populations (unless one assumes they're more hygienic simply by virtue of their race) and the higher rate of asthma in "dirty" urban populations compared to the "clean" suburbs.
And while rural rates of allergy are lower than urban rates, exactly the opposite is true for infectious disease. In other words, the hygiene hypothesis would suggest that difference in antibody and allergy immune response would be the same, but they're not.
As described by Garry Hamilton in NewScientist, this has led some research to rethink the hygiene hypothesis. The current version says that it is exposure to certain innocuous microorganisms that trains the allergy immune response. Rural children have those exposures, while urban children do not. Attention has turned to a new kind of T cell called a suppressor T cell (TS cell).
Before the recent discovery of the Ts cell, immunologists believed that TH1 and TH2 cells had to be forced into action. However, it appears that in fact they have to be held back by Ts cells (hence suppressor T cell). If suppressor T cells are underdeveloped, the other T cells can get out of control. And contact with innocuous microorganisms seems to have something to do with suppressor T cell development.
ENVIRONMENTAL STRESSORS
The theory that environmental stressors actively and permanently disrupt our immune response is as much a complement as it is an alternative to the hygiene theory. Air pollution has received considerable attention as an environmental stressor. The evidence suggests that various forms of air pollution not only trigger asthma attacks, but alter the immune system in a way that promotes the IgE-mediated allergic response. Other research implicates exposure to common herbicides and pesticides.
An example is recent research from Sweden by Carl-Gustave Bornehag, PhD and his colleagues. Bornehag found a significant relationship between phthalates and asthma and allergies. Phthalates are a class of chemicals used to make plastic soft and pliable (specifically, polyvinyl chloride or PVC). It is used in a wide variety of products such as electrical cable, fake leather, IV bags, nail polish, latex adhesives, and vinyl and carpet tile.
Other Swedish researchers, Olle Johansson, PhD and his colleagues have investigated the health effects of electromagnetic frequency radiation (EMF). Over the last 50 years, electrical appliances and electronic devices, radio and television signals, and most recently cell phones and wireless communications technologies have made our environment thick with EMF. Among his findings is an association between EMF and asthma.
Johansson argues that the biological mechanism for the effect is that EMF causes an increase in the number of mast cells, a higher concentration of histamine in those mast cells, and a greater reactivity of those cells. So the same exposure to an allergen today compared to 50 years ago results in a stronger allergic response.
PROTECTION AND PREVENTION
We can reduce the risk of developing allergies and, for those with asthma and allergies, reduce the incidence of attacks. The strategy has two aspects: support of the immune system and protection against exposures.
The first place to start is with diet. Undiagnosed food allergies are common. The symptoms are often ascribed to a disease state like chronic fatigue. The simplest way to test for food allergies is to go on an allergy elimination diet for two or three weeks in which you eliminate commonly allergic foods, especially grains, soy, dairy, and corn. When you reintroduce a food to which you're allergic, you'll have palpable symptoms.
Once you've identified allergic foods and taken them out of your diet, you're immune system is likely to quiet down and will be less likely to react to other allergens.
Asthma and other allergies are often aggravated by oxidative stressors such as air pollution. Oxidative stress is also created by carbohydrates: compared to protein and fat, starchy foods need more oxygen to metabolize. The oxidative process creates free radicals which challenge your body's ability to mobilize the antioxidants needed to neutralize the free radicals. A diet (including supplements) rich in antioxidants contributes to lowering the inflammatory effect of allergies. The most important antioxidants are vitamin C and E, coenzyme Q10, and lipoic acid.
Omega 3 fatty acids are also important in your diet for reducing inflammation, as is using fats and oils for cooking that are rich in saturated fat. Polyunsaturated fats are easily damaged when heated, unlike saturated fat. Those damaged fats contribute to the inflammatory process.
The second place to look is your home environment and the potential exposures to allergens there. Dust is not neutral. It consists of potential allergens. Regularly clean surfaces that collect dust. Replace carpet (which collects dust) with washable rugs. Because mold is a major allergen, keep rooms warm and dry.
Air purifiers can help by precipitating allergens out of the air. However, choose one that doesn't produce ozone--it's an air pollution that creates oxidative stress.
Finally, there are the things you can do to support your body and reduce the effects of allergens. Herbal preparations of stinging nettle taken regularly during pollen season reduces or eliminates symptoms for many. Homeopathic remedies for general and specific allergens are available over the counter. And traditional techniques like a neti pot that keeps sinuses moist also helps support your body's first line of defense.
RESOURCES
Allergy Resources International. Access at http://www.allallergy.net.
Arbes, Samuel et al. 2005. Prevalence of Positive Skin Test Responses to 10 Common Allergens in the US Population. Journal of Allergy and Clinical Immunology. 2005; 116: 377-83. DOI:10.1016/j.jaci.2005.05.017.
Berman, Layna. 2005. Allergy Alternatives. Your Own Health And Fitness. Broadcast April 19, 2005.
Berman, Layna. 2005. Indoor Air Pollution. Your Own Health And Fitness. Broadcast March 1, 2005.
Berman, Layna. 2004. The Hunter-Gatherer Diet. Your Own Health And Fitness. Broadcast March 2, 2004.
Bornehag, Carl-Gustav et al. 2005. The Association Between Asthma and Allergic Symptoms in Children and Phthalates in House Dust. Environmental Health Perspectives. October 2005; 112: 1393-7. DOI:10.1289/ehp.7187.
Hamilton, Garry. 2005. Filthy Friends and the Rise of Allergies. NewScientist. 2495; April 16, 2005.
Solomon, Gina. 2003. Asthma and the Environment. The Collaborative on Health and the Environment. April 10, 2003. Access at http://protectingourhealth.net/newscience/asthma/2003-04peerreviewasthma.htm
