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People who are allergic to birch pollen may react hypersensitively to soy products too

09/2007, 28.06.2007

Physicians should inform their patients about the specific risks of cross allergies

Many people who are allergic to birch pollen are familiar with this problem. When the birch trees blossom, their noses run but even at other times when they have no contact with this pollen, their oral mucosa reacts after eating peanuts and hazelnuts, apples, celery and pulses. The reason: certain proteins in these foods are so similar in structure to the protein in birch pollen that triggers the allergy that the body manifests an allergic reaction to them, too. The term used to describe this phenomenon is a cross allergy. These forms of allergies are increasingly being observed amongst people with a birch pollen allergy. “Physicians who diagnose their patients as suffering from a birch pollen allergy should, therefore, explain to them that they could also be allergic to soy products”, says Professor Dr. Dr. Andreas Hensel, President of the Federal Institute for Risk Assessment (BfR). Consumer initiatives and self-help groups should also inform allergy sufferers about this risk. BfR does not believe that it makes sense for the packaging of soy products to carry specific warnings about possible cross allergies as soy must already be labelled as an ingredient in foods.

The number of soy products on the market has steadily increased in recent years. Soy is considered to be a healthy food. It is not just people on a vegetarian or vegan diet who frequently opt for soy products. Patients with a lactose intolerance or who are allergic to milk protein buy soy products as a substitute for dairy products. They will scarcely expect the soy alternative to harbour a risk of allergies, too. Around 0.4 percent of the population have an allergic reaction to these products. The reaction is either triggered by the soy protein itself – this is called a primary reaction – or is a cross allergy. In this case other allergens like pollen are responsible for the primary allergic reaction. 

People with a birch pollen allergy are especially prone to these cross-reactions. The trigger of the cross allergy to soy is a protein (the PR-10 stress protein Gly m 4), which is found in soybeans and is similar in structure to the birch pollen allergen Bet v 1. Typical symptoms of an allergic reaction to the Gly m 4 protein are itching and swelling of the oral and pharyngeal mucosa directly after eating soy products. Skin rashes or gastro-intestinal disorders may follow. Highly sensitised individuals may experience severe allergic reactions, in individual cases even anaphylactic shock coupled with serious circulatory disorders.

The activity of the soy protein Gly m 4 can be dampened through heating to high temperatures or the protein itself can be destroyed. Allergy sufferers can, therefore, eat most products with soy ingredients which were heated during processing without suffering any health disorders.

BfR does not believe that it makes sense for the packaging of soy products to carry additional warnings for allergy sufferers. Not all soy products contain the protein Gly m4 that triggers the allergy. At the present time, no official detection method is available. Furthermore, besides soy numerous other foods could trigger a cross allergy in people with a birch pollen allergy. They include apples, strawberries, hazelnuts, carrots and celery. There have been reports of particularly severe cross-allergic reactions in conjunction with the consumption of peanuts. Warnings on soy products would not, therefore, protect people who are allergic to birch pollen from a cross allergy.

As the cross-allergic reactions of people with a birch pollen allergy to soy products may involve serious allergic symptoms, BfR recommends that physicians, consumer initiatives and self-help groups include soy in their general information about cross allergies with foods and that they specifically inform people with a birch pollen allergy about this risk. As soy ingredients must be indicated on the labels of all foods, the consumers affected will then be able to avoid foods that are critical for them.


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