Allergies are a major cause of illness around the world. In the United States, 50 million people have some type of allergy, this includes millions of children. In the USA alone, there are 2 million missed school days because of allergies.
When the body identifies an allergen, it treats it as an invader and tries to fight it off. To do this, the immune system makes antibodies called ‘immunoglobulin E’ which causes cells to release chemicals like histamine into the bloodstream to attack the substance. Unfortunately, this can cause symptoms that range from a minor annoyance to serious and even life-threatening. But why does our body react in this apparently self-damaging way?
Common food allergens
According to the National Health Service (UK) almost any food can trigger an allergic reaction. However, there are certain foods that are known to cause more allergies than others. These include:
- tree nuts
- some fruit and vegetables
Types of food allergies
Food allergies are divided into three different types, depending on the symptoms and how long the reaction takes to show. The most common type is triggered by the immune system producing an antibody called immunoglobulin E (IgE). This is often known as IgE-mediated food allergy and is recognised by symptoms occurring a few seconds or minutes after eating the allergen. This type of allergy is the one most associated with an increased risk of anaphylaxis.
The second type of allergy is a non-IgE-mediated food allergy. These allergic reactions are not caused by immunoglobulin E, but by other cells in the immune system. It’s categorised by a delay in symptoms after eating the allergen - sometimes up to several hours. Finally, the last type of allergy is defined as mixed IgE and non-IgE-mediated food allergies, these allergies happen when you experience symptoms from both types.
Allergy vs intolerance
Food intolerance isn't the same as food allergy. Although food intolerances can have some pretty uncomfortable side effects, they’re actually caused by difficulty digesting certain substances rather than an allergic reaction. Some important differences between intolerances and allergies include:
- the symptoms of a food intolerance usually occur several hours after eating the food
- you need to eat a larger amount of food to trigger an intolerance than an allergy
- a food intolerance is never life threatening, unlike an allergyYou can read more about food intolerance on the NHS website.
On the other hand, a food allergy occurs when the body’s immune system reacts to a specific food. Sometimes these reactions are mild but in rare cases they can be very serious and even life-threatening. Compared to the symptoms of a food intolerance, which are stomach cramps and diarrhea, symptoms of a food allergy can affect more of the body. Some symptoms of food allergy include:
- an itchy sensation inside the mouth, throat or ears
- a raised itchy red rash (urticaria, or "hives")
- swelling of the face, around the eyes, lips, tongue and roof of the mouth
How do genetics affect allergies?
At the moment, there are about 9 polymorphisms in genes that have been linked to food allergies. According to Hong et al, because of this, there is compelling evidence that genetic factors play a role in whether or not a person has a food allergy. However, there are currently many more advancements happening in other areas of allergy research, like with asthma and eczema, so food allergies have had less attention. Hong suggests that more studies will be needed in the future to help us find out which specific genes can influence food allergies and even suggests that a genome-wide association approach might be a really powerful way to do this.
On a more positive note, research into eczema and asthma could actually help us learn more about the genetics of food allergies too. This is because there is a strong link between eczema and food allergy, for example, most children who have a food allergy also experienced eczema during infancy. Overall, eczema is considered a genetic condition as it is often passed down in families, so creating these kinds of links with food allergies suggests that the same might be true for them too.
Another study which supports this theory was conducted by Brown et al. It showed that IgE-mediated peanut allergy has strong heritability and is associated with other loss-of-function mutations within the filaggrin gene which have been linked to allergies like eczema and other skin conditions. Since eczema and food allergies often come as a package deal, this area is currently getting most of the attention when it comes to research in food allergy.
In a different study conducted by Dr Xiaobin Wang and her colleagues at the Johns Hopkins Bloomberg School of Public Health, 2,759 DNA samples were analysed to search for clues about which genes might contribute to an increased risk of developing food allergies. They managed to locate genes on chromosome six that are linked to peanut allergy. This study suggests that the HLA-DR and -DQ gene region likely poses an increased genetic risk for peanut allergy as it accounted for about 20% of peanut allergy in the study sample. Interestingly, this is also the same location that predisposes people to an increased risk of coeliac disease.
Recently, another study looking into peanut allergy has been the first to link a known gene called c11orf30/EMSY (EMSY) to food allergy. EMSY has already been linked to eczema, asthma, and other allergy-related conditions, and the new discovery supports the idea that it has a wider role in predisposing people to allergy generally.
To find out more about specific SNPs that have been linked to food allergies, head over to our personalised reports and see what your genes say about your predisposition to specific allergens.
Studies such as these reveal that there are at least some genetic influence on food allergies, however more research is needed to make direct links. Continuing research into food allergy could really have a big impact on health worldwide, considering that such a large percentage of people are affected by at least one.