Allergies, such as asthma, food allergies and eczema are a plague of our modern society, affecting between 20 and 30 percent of the population in western countries. The prevalence of those allergies has significantly increased in the past few decades, raising questions about the causes of such epidemics.

What are allergic reactions?

Allergic reactions result from an inappropriate and exacerbated response of the immune system to an environmental or food substance, or antigen, otherwise considered harmless. Allergies involve an immune response mediated mostly by Immunoglobulins E or IgE, which triggers a series of reactions leading to the release of histamine by the mast cells and other symptoms characteristic of allergies.

It is still largely unknown why some people develop allergies. Heredity is one factor, which predisposes an individual to become allergic, although not necessarily to the same substances as the parents. Recent theories implicate dysfunctions of two types of T cells (lymphocytes that are produced in the Thymus), namely T-helper cells and regulatory T-cells.

Why is the prevalence of allergies increasing?

It has been postulated that one of the main reasons why allergies are more frequent and increasing in western countries is the reduced microbial exposure of the immune system. This hypothesis is known as the “hygiene hypothesis”. According to this idea, lifestyle factors such as diet, antibiotic use, vaccinations and improved hygiene are causing our immune systems to become hypersensitive to foreign substances, when encountered. Studies have shown that being raised on a farm reduces the risk of developing allergies such as eczema and asthma later in life, and that being born in the United States predisposes to a variety of allergies.

How are probiotics linked to immunity?

The gut flora or intestinal microbiota (consisting of microorganisms living in the digestive system) plays very important roles during infant development, including  digestion (digestion of undigestible fibers), immune development, control of intestinal epithelial cell growth and differentiation, and release of essential vitamins.

The intestinal microflora is critical to the maturation of the gut-associated lymphoid tissue (GALT). The GALT is the immune center of the digestive system and represents the largest mass of lymphoid tissue of the body, in which lymphocytes T and B are stored. The gut microflora helps the GALT by presenting a wide variety of antigens and promoting tolerance toward harmless substances such as foods. Therefore gut bacteria actually participate in the programming of appropriate immune responses of their host.

When the gut microflora is unbalanced or deficient (for example after the use of antibiotics) the GALT does not mature correctly. Differences in the composition of gut microflora between allergic and non-allergic populations have also been observed. Probiotics have the potential to modulate the balance of gut bacteria, Probiotics supplementation can reduce pathogenic and increase beneficial bacteria in the gut microflora of allergic infants.

Does probiotic supplementation reduce allergies? 

Animal studies

The use of probiotics in animal models of allergies shows promises. Probiotic supplementation of pregnant mice and their newborn resulted in decreased clinical symptoms and IgE levels in a model of eczema (atopic dermatitis). The study of a mouse model of asthma showed improved lung function and reduced eosinophil numbers with the use some probiotics, although not all produced the same effect. Reduced food allergy symptoms were also obtained when probiotics were administered to pig models of egg allergy and mouse models of shrimp allergy. However, as promising as those studies are, beneficial effects in animal models do not always translate to equivalent responses in humans.

Clinical studies

The use of probiotics in mothers and their newborns has been shown to prevent the development and to reduce the severity of eczema. Indicative of promising results, a study demonstrated that probiotics increase gut-specific IgA responses, which are frequently defective in children with food allergy. Effects of probiotics on asthmatic individuals still remain to be validated though, which could be due a difficulty in finding optimal strains of bacteria, doses, and duration of treatment.

In conclusion, the use of probiotics is showing great promises to prevent allergic diseases and to reduce their impact, in particular for atopic dermatitis or eczema, and food allergies. The use of foods with anti-histamine properties can also be considered in a diet aiming at reducing allergy symptoms.

Dietary sources of probiotics

Probiotics can be found as supplements, in the form of wafers, pills or powders, and are very often based on dairy sources. Some probiotic supplements are labeled dairy-free but might still be grown on dairy and thus might be safe for lactose-intolerant people and not be for people with dairy protein allergies. If you need or want to avoid dairy, you need to check the label and look for probiotics grown on non-dairy sources such as oats.

Dietary sources of probiotics offer the same options: grown on dairy or dairy-free.

Dietary sources of probiotics grown on dairy include yogurt and dairy kefir.

Dairy-free sources of probiotics include sauerkraut, dark chocolate, microalgea, miso, tempeh, pickles, Kimchi, Kombucha tea, water kefir, coconut kefir, and ginger beer.

References used in this article

Toh ZQ, Anzela A, Tang ML, Licciardi PV. Probiotic therapy as a novel approach for allergic disease.Front Pharmacol. 2012;3:171. doi: 10.3389/fphar.2012.00171. Epub 2012 Sep 21.