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Food Allergens: Avoidance or Exposure?
By _______________________
Biology 40S
Ms. Heidi Redfern
January 17, 2014
Food allergies significantly impact many individuals in society. Infants and young children
are particularly vulnerable as food allergies often develop in the early stages of life. Controlling
food allergen exposure among children is crucial as reactions to food allergens can be serious and
potentially fatal. In fact, food allergy is the most common cause of anaphylaxis outside a hospital
setting (Lack). For precautionary reasons, food allergen avoidance has been recommended for
infants and young children in an effort to prevent the development of food allergies. However, this
traditional paradigm continues to be practiced despite accumulating evidence of increasing allergy
rates in society. An examination of the biological mechanisms of food allergies, the traditional
paradigm of allergen avoidance, and emerging research supporting early allergen introduction,
suggests that a new approach is required. Although more research is needed, early exposure to food
allergens may actually reduce the risk of children developing food allergies.
The Biology of Food Allergies
An allergy is a hypersensitivity to a certain substance. Many food allergies are mediated by
immunoglobulin E (IgE) because IgE antibodies can bind to many different food proteins (Mader
248). Small amounts of IgE antibodies are essential to the human body and serve as defense
mechanisms against parasites. However, too many IgE antibodies stimulate an immune response
that can harm the body. Sensitization occurs when an individual is exposed to a food allergen that
stimulates excessive IgE production. The allergen-specific IgE antibodies attach themselves to mast
cells found in the tissue and white blood cells called basophils. During this phase, the body
prepares itself to react to the specified allergen and symptoms are not yet apparent (Baumert).
An allergic reaction occurs when an allergen binds to the primed IgE antibodies. The IgE
releases histamine and other substances into the bloodstream (Mader 248). In small amounts,
histamine is not dangerous to the human body; in fact, it plays an important role in the body’s
inflammatory response. Histamine causes vasodilation, a process in which blood vessels widen to
allow white blood cells efficient access to the infection site. Histamine also removes infectious
agents and allergens by inducing fluid secretion at the infection site (Pollock). However, once the
body has become sensitized to a particular allergen, unusually large amounts of histamine are
released, which cause symptoms associated with an allergic reaction. These symptoms include
hives, swelling, wheezing, nausea, and anaphylaxis.
The body does have its own natural tolerance mechanisms toward food allergens. An
allergic response does not occur if immunoglobulin G (IgG) antibodies bind to the allergen before
IgE. An IgG-activated response is a healthy and effective means in which the body eliminates
potentially harmful substances. IgG protects the body by attaching to foreign particles, making it
easier for other immune cells to destroy them. White blood cells known as T-helper (Th) cells also
function in acquired immunity (Mader 248). In rodents, it has been found that Th1 cells suppress
IgE antibody formation while Th2 cells are linked with IgE production. Therefore, low IgE
responders are typically Th1-dominant and high IgE responders are Th2-dominant. It is
hypothesized that this theory also applies to humans. Therefore, the levels of Th1 and Th2 cells
may affect the magnitude of the body’s IgE response. A Th1-dominant individual may be less
likely to develop a food allergy (Zeiger).
Traditional Paradigm: Early Avoidance of Food Allergens
The traditional paradigm of food allergen avoidance has been favoured and practiced for
some time. Pediatricians have suggested that parents delay the introduction of highly allergenic
foods in children. For instance, it is recommended that eggs and fish are not introduced until one
year, and nuts avoided for up to three years (Arshad 115).
This particular paradigm of allergy prevention is based upon observations that allergies are
often developed at a very young age. The production of IgE begins already in the eleventh week of
gestation. Subsequently, specific IgE responses directed to food proteins may be observed during
the first months of life (Hamelmann 234). It seems that a critical period exists early in life in which
infants may be particularly prone to developing sensitization and excessive IgE levels (Pollock).
The identification of this early critical period led to the theory that avoidance of food
allergens in infants and young children could prevent the development of allergies. Some studies
seem to confirm this. One study found that the development of cow’s milk allergy in at-risk infants
was reduced when cow’s milk was avoided in early infancy. Another study observed that the
likelihood of peanut sensitization was increased with maternal consumption of peanuts during
pregnancy and an early introduction to peanut in the infant’s diet (Arshad 114-115).
These facts prompted the institution of early preventive efforts by removing common food
allergens from the diets of young children. Strict avoidance can, however, be difficult and onerous.
It requires close supervision of a child’s diet by parents and health care workers. Even so, complete
avoidance of certain allergens may prove difficult as small amounts of the specified food proteins
can be present in many packaged or prepared foods (Arshad 115). Due to these difficulties, strict
programs of allergen avoidance have been specifically directed toward infants at high risk.
Targeting these individuals can be challenging, as an examination of family history remains the
only effective method of determining those at high risk of developing an allergy. Nevertheless, the
practice of allergen avoidance has been considered worthwhile because it was believed to be
effective.
This paradigm has been practiced long enough to collect significant statistical data regarding
the incidence of food allergies in young children. Despite practices of food allergen avoidance, the
prevalence of food allergies has continued to rise and give cause for concern. Over the past few
decades, the rate of food allergen sensitization among children in western countries has not fallen,
but has significantly increased (Allen, Campbell and Kemp 415). In Great Britain, one study
revealed that the rate of peanut allergies among children tripled between 1989 and 1996. Another
study published in New York showed that the prevalence of peanut allergy among American
children doubled between 1997 and 2002 (Hamilton 34). These undeniable realities have raised
serious questions regarding the efficacy of food allergen avoidance.
New Paradigm: Early Exposure to Food Allergens
New research suggests that early exposure to, rather than avoidance of, food allergens may
be the key to reducing the risk food allergy development in children. Maternal exposure to potential
food allergens during pregnancy, oral exposure during early childhood, and immunotherapy
methods for treatment of allergies, all suggest the benefits of early exposure to food allergens.
Ingestion of food allergens by a pregnant woman may be beneficial to her unborn child. In
animals, maternal IgG has been shown to have a suppressive effect on food allergen sensitization in
the fetus. One study proposes that maternal IgG antibodies may be transferred through the placenta
to the fetus during gestation. Therefore, avoiding food allergens during pregnancy may prevent the
fetus from acquiring potential IgG levels. Correspondingly, maternal food allergen avoidance may
instead favour an increase in food-specific IgE levels in the infant (Allen, Campbell and Kemp
419).
For infants, early oral exposure to potential food allergens may reduce the sensitizing effects
of topical exposure. According to the “dual-allergen-exposure hypothesis,” the ingestion of food
promotes tolerance while topical exposure facilitates sensitization (Matsumoto and Saito 292). One
study found that infants with environmental, but not oral, exposure to peanuts had greater risk of
developing a peanut allergy (Chan and Cummings). Therefore, the effects of cutaneous exposure to
food allergens may be heightened if the potential allergen has not already been introduced orally.
This research may give parents incentive to orally expose their children to food allergens early in
life.
The practice of immunotherapy may also support the early allergen exposure approach.
Immunotherapy uses frequent, escalating doses of food allergen to develop tolerance. The goal is to
divert the immune response from a Th2 to a Th1 type in order to reduce the production of IgE and
increase the production of IgG (Janeway, Travers and Walport). Immunotherapy promotes
exposure to allergens rather than avoidance. Perhaps, then, exposure to allergens may not only be a
treatment for allergies, but also a preventative measure in early childhood.
Some clinical studies support this theory of food exposure as a method of allergy prevention.
The Journal of Allergy and Clinical Immunology published a prominent study regarding peanut
exposure among Jewish children living in Israel and the United Kingdom (Payne 34). The
prevalence of peanut allergy was significantly lower among the Israeli children, who had been
exposed to peanuts during early weaning and consumed peanuts frequently. Children from the
United Kingdom, who had avoided peanut consumption, were more likely to develop a peanut
allergy (Wennergren 1085).
While there is growing evidence for early exposure as a method of allergy prevention,
pediatricians are not yet comfortable in changing their recommendations of food allergen
avoidance. At present, therefore, decisions regarding early exposure must be individualized and
based on parental comfort level (Chan and Cummings). More research and clinical studies are
required to develop firm conclusions and to convince medical practitioners of this new paradigm.
Conclusion
Understanding the biological mechanisms associated with food allergen sensitization and
reaction is critical in developing the best clinical recommendations for allergy prevention.
Although more research is needed to determine whether the body responds best to allergen
avoidance or exposure, it is clear that the rising rate of food allergies in society has coincided with
the practice of early food allergen avoidance. The consequences of allergic reactions increasingly
impact young children and their families, and for this reason, the traditional paradigm must be
challenged. As Allen, Campbell, and Kemp suggest, researchers should turn their attention towards
early exposure, exploring the doses and forms of food allergens which will encourage the natural
tolerance mechanisms of the human body (420). It is time to reinvestigate methods of food allergen
introduction in an effort to establish an effective, preventative measure that will benefit young
children and their families.
Bibliography
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