The New Pandemic: We have all heard the story: the prevalence of allergic disease has dramatically increased over the past generation. In the United States allergic disease (atopic dermatitis, food allergy, allergic rhinitis or “hay fever,” and allergic asthma) affects 20% of the population. As mothers we want to know why and what do we do for our generation of children afflicted with these conditions. I want to share with you some of the medical and scientific communities’ latest research regarding these issues. It is an exciting time of discovery but the answers are still unfolding for some of the specific questions. Fortunately, as the prevalence of these diseases rise, so does the support network and information sources for mothers of children with allergic disease.
So many of my patients’ moms tell me when they were children they knew of 1-2 total kids with nut allergies and now there are 1-2 if not more children per class with nut allergies. Allergic asthma runs rampant among school age children, especially those living in inner city environments. Allergic nasal symptoms not only contribute to persistent upper airway congestion, increased risk of sinus and ear infections but also can contribute to poor sleep and poor school or work performance. Studies from the last decade estimate a total of 3.5 billion dollars per year spent on prescription drugs, over the counter allergy medication, and allergy related health care provider visits. Allergies affect cost in other ways with billions of lost dollars resulting from absenteeism from work or school. Clearly the effects of allergic disease go beyond the nose, lung and skin. So the big question is “what is going on?” In order to understand the current theories, it is imperative to note that allergic disease results from a complex interaction between genetics and environmental factors.
Eat Dirt, the Wonderful World of Microbes: The leading theory for the increase in allergic disease is referred to as the “hygiene hypothesis.” The crux of this theory is that our current society’s “clean practices” (smaller family size, less early life exposure to farm animals and dirt in general, and increased use of antibiotics) is skewing the infant’s immunologic development toward allergy. It appears that an individual’s immunologic fate is highly influenced in the first year of life. The big player in this fate is the infant’s gut. The gut is the largest immune organ in humans and in the first several months of life undergoes enormous change including population with bacteria. Everything from the route of birth (Vaginal versus C-Section), feeding practice, antibiotic exposure, home environment, and early life animal exposure, especially livestock exposure, influences the number and species of resulting gut bacterial colonies. The gut microbial flora’s mingling with outside world’s ingested substances is thought to shape early immune development. We have all observed our infants happily mouthing objects in the outside world. The infant’s gut is thought to be the first place where the body either ignores things or makes immune responses against them. The consequence from the hygiene hypothesis’ viewpoint is that the microbial equation necessary for tolerance to innocuous substances (food or environmental pollens), has been violated.
Pollution, Dust mites, and Cockroaches, oh my!: Additionally, other outside influences may also turn on the genes for allergy. Elevated levels of certain airborne allergens such as dust mites and cockroaches are associated with increased risk of nasal allergies, atopic dermatitis, and asthma. Furthermore, some air pollution components, namely diesel exhaust particles, have also been associated with elevated rates of allergic disease and asthma. Feeding practices among various cultures differ and it is hypothesized that this may also influence the development of food allergy. As an example, peanuts in the United States tend to be dry roasted. This type of preparation may enhance the “allergic-ness” or as we say in the business, the” immunogenicity”, of peanuts. Peanuts in some cultures with lower peanut allergy rates are boiled or introduced as a powdered ingredient in a first baby food. Finally, there are some preliminary studies looking at the pollen consequences of increased temperatures and environmental CO2 levels. These studies have demonstrated increased growth of allergic trees towards polar latitudes, earlier tree pollination, and increased amounts and immunogenicity of specific pollens.
Clearly both individual and global factors are occurring. What is unclear is the relative contribution of each to an individual’s case. As you can see this is a complicated problem to dissect but there are intriguing studies attempting to pinpoint the sentinel events shaping immune development. The hope is that future studies will be able to shed light on a primary prevention strategy for allergic disease.
The first year: pregnancy, breastfeeding, formulas, solid food introduction, and pre/probiotics. Infants are considered to be at risk of allergic disease if at least one parent or sibling has any form of allergy (atopic dermatitis, food allergy, allergic asthma, allergic rhinitis). There have been studies done looking at the effect of maternal avoidance of cow’s milk, egg, or peanut during pregnancy and breastfeeding. The take home message from these studies is that single food maternal restriction of cow’s milk, egg, or peanut in pregnancy and breastfeeding does not reduce risk for future development of allergic rhinitis, asthma or food allergy in the infant. There is one further piece of data worth mentioning. There are a couple of small studies looking at more intense allergen avoidance strategies for mothers. These studies look at maternal dietary restriction of several foods during pregnancy and breastfeeding including cow’s milk, egg, and nuts (and fish and soy in some studies). These studies also included environmental dust mite avoidance strategies. The more intense diet avoidance paired with the dust mite environmental control measures seem to have a more pronounced effect on the prevention of atopic dermatitis, asthma and allergic rhinitis and a trend towards reduction in food allergy in the infants. This approach has to be undertaken with caution to ensure the mother’s diet is nutritionally complete and would need further discussion with an allergy specialist to determine if it is worthwhile to pursue.
Several questions regarding infant feeding practices have also emerged. Breast milk is the ideal source of nutrition for the first 4-6 months of an infant’s life. Breast milk may have a protective effect on the development of certain food allergies and is associated with decreased wheezing in children during the first 2 years of life. When exclusive breast feeding is not possible or preferred, the infant is given formula. There are a variety of formulas out there including cows milk formula, soy formula, and more predigested(called hydrolyzed) cows milk formulas. At the extreme predigested end are amino acid based formulas. Current studies suggest that if breastfeeding is not an option or if formula supplementation is done in high risk infants, a partially or extensively predigested formula is preferred over regular cow’s milk formulas or soy formulas. Amino acid formulas are reserved for infants with several already established food allergies. In addition, several moms have questions regarding when to introduce solid foods. The window of opportunity appears to be between 4-6 months, even in infants at high risk for allergic disease. The practice of delaying introduction of solid food beyond 6 months has not been effective at prevention of allergic disease. Introduction of rice cereal, fruit, vegetables and meat constitute the usual first solid foods in an infant’s diet.
Finally there is a lot of buzz out there about prebiotics and probiotics. Prebiotics are nondigestable carbohydrates that stimulate the growth of one or a limited number of beneficial gut bacteria. Probiotics refer to a specific strain or groups of strains of beneficial gut bacteria. Prebiotics and probiotics are found in breast milk, can be added to infant formulas, are available as over the counter supplements, or are ingredients in specific foods such as yogurt. The idea is that populating the infants gut with beneficial bacteria may steer the future immune development away from a food or environmental allergic response. While this approach certainly holds promise, the exact way of how to do this, when to do this(again, there may be a limited window of time), and what is the best combination of administered bacteria is unknown.
I want to emphasize that the above information applies only to infants at risk of allergic disease rather than those with established allergic disease such as atopic dermatitis. The specific feeding practices in those infants differ and require consultation with a medical professional. Also all the data mentioned above refer to population based studies rather than to individual cases. The best approach to your specific situation will depend on you, your family, your living practices, and an informed discussion with your health care provider.
Check back next week for Part II: “The Cat is Out of the Bag”