Several Factors Linked to Development of Peanut Allergies
The prevalence of childhood ]]>peanut allergies]]> appears to have increased in the past few decades. Peanuts are currently the leading cause of severe allergic reactions caused by a food. Peanut allergies affect about 1.5 million people in the United States, about 50 to 100 of whom die each year from ]]>anaphylactic shock]]> caused by accidental peanut ingestion. Simply avoiding peanuts is not foolproof for many of these people. Peanut allergies can be extremely severe; eating half a peanut or a non-peanut product contaminated by peanut protein during manufacturing, or even kissing someone who has eaten peanuts have all been known to produce symptoms in people with peanut allergies.
Other than a family history of peanut allergy and the presence of atopy (a hereditary tendency to produce antibodies to specific allergens—such as peanuts), there are no known risk factors for peanut allergy. Some evidence suggests that maternal consumption of peanuts during pregnancy and a child’s consumption of peanuts or peanut oil during his or her infancy can increase a the risk of developing a peanut allergy. However, these findings have not been replicated in rigorous clinical studies. A link to consumption of soymilk and soy formula has also been suggested because peanuts and soybeans both belong to the legume family.
Researchers from St. Mary’s Hospital at Imperial College, London and from the University of Bristol in the United Kingdom sought to identify factors from early pregnancy through childhood that could increase the risk of a child developing a peanut allergy. In a study published in the March 13, 2003 New England Journal of Medicine , they report the following factors may influence the development of childhood peanut allergy: family history of peanut allergy, consumption of soymilk or soy formula during infancy, early onset of the skin condition eczema, other rashes with oozing or crusting, and exposure to skin creams or lotions containing peanut oil.
About the Study
The researchers used data from the Avon Longitudinal Study of Parents and Children, which enrolled pregnant women who delivered children between April 1, 1991 and December 31, 1992. The 13,971 children who were born to these women became part of the study and have been followed from the time of their birth.
Data on study participants was collected from regular questionnaires, telephone interviews, medical records, and biologic samples including saved blood from the umbilical cord at the time of birth. Mothers answered questions about personal and family history of peanut allergy and peanut consumption during and after pregnancy. They also answered questions about rashes that their children experienced, medications given to their children, and details of the children's diet.
The study researchers initially collected data on all study participants. They then identified children who were thought to have peanut allergies and confirmed these allergies through skin testing and double-blind, placebo-controlled food challenges.
The umbilical cord blood of children with confirmed peanut allergies was checked for the presence of IgE, an antibody involved in allergic reactions to peanuts.
To determine what may increase the risk of developing peanut allergies during childhood, the researchers compared the children with peanut allergies against two sets of control children without peanut allergies:
- A random sample from the initial study population
- Children whose mothers had a history of eczema and who had eczema themselves during the first six months of life
Maternal history of atopy, ]]>asthma]]> , peanut allergy, or specific allergies other than to peanuts, significantly increased the chances that their children would develop a peanut allergy.
The researchers found no peanut-specific antibody in the blood from the umbilical cord. They also did not find evidence linking consumption of peanuts by the mother during pregnancy or breastfeeding to the development of peanut allergies in their children.
High levels of consumption of peanuts by infants also did not appear to increase the risk of peanut allergy.
Compared to the normal control group, children with a confirmed peanut allergy were:
- 2.6 times as likely to have consumed soymilk or soy formula during infancy
- 2.6 times as likely to have had rashes over joints and skin creases
- 5.2 times as likely to have had an oozing and crusting rash
In addition, children with confirmed peanut allergies were significantly more likely to have been exposed to topical creams containing peanut oil during their first six months of life compared to the normal control group (91% versus 59%) and compared to the eczema control group (91% versus 53%).
One important limitation of this study is that questions about maternal consumption of peanuts during pregnancy were not asked until after the presence of peanut allergy had been confirmed in their children.
How Does This Affect You?
This study suggests that the use of prescribed and over-the-counter creams and ointments containing peanut oil may increase the risk of peanut allergy in children. Physicians and parents should be aware of this association and should choose creams and ointments that do not contain peanut oil, especially if there is a maternal history of allergy. They should also bear in mind that topical exposure to peanut allergens in other forms—for example, contact of an infant’s skin to peanut butter—could increase risk of peanut allergy.
Also according to this study, there appears to be an increased risk of peanut allergies for children who consume soymilk or soy formula during infancy. However, the benefits of soymilk or soy formula—to children who are allergic to cow’s milk, for example—usually outweigh this small risk. Parents should speak to their pediatricians before making any decisions.
Although its reassuring that the researchers did not report that maternal consumption of peanuts increases the risk of peanut allergies in children, we cannot conclude from the study that eating peanuts during pregnancy poses no risk. While it may be prudent for expecting mothers avoid large quantities of peanuts, it is highly unlikely that the occasional unplanned peanut will be harmful.
While this study focused on potential ways to prevent future peanut allergies, a companion article also published in the March 13, 2003 New England Journal of Medicine addressed a new method of treating patients who already suffer from peanut allergy. In this randomized, double-blind, placebo-controlled study, researchers injected peanut allergy sufferers aged 12-60 years with varying doses of TNX-901. This so called monoclonal antibody is capable of interfering with the allergy-producing activity of IgE antibody. They found that a 450 milligram (mg) dose injected every four weeks for four doses significantly increased tolerance to peanuts. Whereas it normally took an average of half a peanut to begin producing allergic symptoms, it took an average of almost nine whole peanuts after the subjects took the TNX-901. This therapy is not likely to reach consumers for a few years, but when it does, it should help quell the fears of accidental peanut ingestion in children and adults with deadly peanut allergies.
National Institute of Allergy and Infectious Diseases
National Institutes of Health
The Food Allergy and Anaphylaxis Network
Lack G, et al. Factors associated with the development of peanut allergy in childhood. NEJM . 2003;348:977-985.
Leung DYM, Sampson HA et al. Effect of anti-IgE therapy in patients with peanut allergy. NEJM . 2003;348:986-993.
Last reviewed Mar 13, 2003 by ]]>Richard Glickman-Simon]]>
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