Why are children likelier to develop food allergies?
Food allergy or intolerance can cause symptoms ranging from a harmless skin rash to a potentially lethal anaphylactic shock. An estimated 15 million Americans suffer from food allergies, many of them children.
The prevalence of food allergy is higher among children and is estimated at 6 to 8 percent in children younger than 3 years and 3 to 4 percent in the adult population. Common childhood food allergies like milk and egg are commonly outgrown by late childhood, but allergies to peanut, sesame seeds and tree nuts are more persistent, with fewer than 20 percent developing tolerance. A new study published in the January 28, 2016, online issue of the journal Science by researchers at La Jolla Institute for Allergy and Immunology may explain why children may be at higher risk for food allergy and how food tolerance emerges over time in normal individuals. The study essentially shows one mechanism by which food tolerance may be acquired which involves specific populations of T cells called regulatory T cells, or Tregs, that develop following food consumption. Without them, we would mount a strong immune response to macromolecules contained in food.
The research could explain why children, who have more limited exposure to different types of novel nutritious macromolecules (that is, food) than adults, are more susceptible to food allergies. It also suggests what happens on a cellular basis as some outgrow it: namely, they may be expanding their repertoire of Tregs that recognize new foods as “safe”.
Why are children likelier than adults to develop food allergies?
Because of their age and relatively immature immune system, children are more at risk for the development of food allergies. The exact reason is still not fully understood.
Antibodies are proteins manufactured by the body that help fight against foreign substances called antigens. When an antigen – like a foreign food or protein – enters the body, it stimulates the body’s natural defense system immune system to produce antibodies.
Despite the extent of exposure to the foreign proteins we eat, relatively few patients have food allergies. Instead, most develop a normal form of oral tolerance in which the immune system is unresponsiveness to everyday ingestion of harmless antigens.
Disturbances at various steps along the pathway of oral tolerance can result in food sensitization and food allergy. For example, oral tolerance begins with the basic process of digestion and absorption, which prevents most food antigens from presentation to the immune system. Food proteins that enter the gut are digested and absorbed, and proteins that escape digestion generally pass through the gut without incident. This is due to the mucosal barrier that lines and protects the gastrointestinal tract, as well as partial degradation of these proteins by gastric acid. Because infants secrete less stomach acid and they have a somewhat increased intestinal permeability, among other factor, their risk of sensitization and allergy is increased.
Are children more susceptible to food allergies when they have limited exposure to novel foods?
The field of allergy has recently shifted into encouraging early introduction. A recent study in the New England Journal of Medicine showed that children at risk for food allergy were significantly more likely to develop peanut allergy if they avoided peanut rather than introduce it and keep it in the diet. There may be a critical window which is optimal for food introduction. It is still recommended that children be exclusively breast or formula fed for the first 4 to6 months of life, but subsequent to that period, food introductions should begin.
How can we help children develop food tolerance?
Parents should offer children a diverse and healthy diet early. Children at risk for food allergy may have to be more cautious, but should not delay introductions. If concerned, consultation with an allergist may helpful.
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