How do probiotics and prebiotics work?

Probiotic products have living bacteria in them, such as lactic acid bacteria. It is thought that they have a positive effect on gut flora, and that this can prevent allergy-related diseases from developing later on. Prebiotics are mainly indigestible carbohydrates such as oligosaccharides, which stimulate the production of healthy bacteria in the digestive tract. Probiotic and prebiotic products are available in the form of tablets and drinks, and are sometimes found in dairy products such as yogurt.

An international group of researchers was commissioned by the World Allergy Organization (WAO) to analyze studies on the preventive effect of probiotic and prebiotic products on allergies and eczema. The WAO is a global umbrella organization of nearly 90 national medical societies that deal with allergies.

The researchers wanted to find out whether a child's risk of developing eczema or an allergy is reduced if

• the mother takes prebiotics or probiotics while pregnant,
• the mother takes prebiotics or probiotics while breastfeeding, or
• the child is given baby formula containing prebiotics or probiotics after birth.

Research on probiotics

The researchers analyzed a total of 29 studies that tested the effect of probiotics on eczema and allergic diseases. It wasn't always possible to get separate answers to the questions they were looking into because the probiotics were used in combination in most of the studies: In other words, the mothers either took probiotics during pregnancy and while breastfeeding, or both the mothers and their babies received probiotics.

The studies that used the probiotics like this suggest that they can prevent eczema. About 6 to 14 out of 100 fewer children developed eczema by using probiotic dietary supplements.

But the studies left some questions unanswered: The different strains of bacteria were examined separately or in combination, for example Lactobacillus rhamnosus and different types of Bifidobacteria. Based on this data, it's not possible to tell whether the various types of bacteria have different effects or what the best dose would be.

Also, the studies mostly involved pregnant women, mothers and babies who had a higher risk of allergic disease because it runs in their family. There is hardly any research on whether probiotics can also protect people in families with a low risk of allergies.

The researchers also looked into possible side effects of probiotics, such as nausea, constipation, diarrhea and rashes. They didn't find that probiotics increased the risk of these types of side effects, but the studies didn't provide enough information on side effects overall.

Wold Allergy Organization recommendations on probiotics

Based on the study data, WAO has issued recommendations: The recommendation is for the prevention of eczema in children who have a genetic predisposition. They are considered to have a predisposition if at least one parent or sibling has an allergic disease such as hay fever, eczema, asthma or a food allergy. If a baby has this kind of increased risk, the WAO recommends that their mother uses probiotics in the final trimester of pregnancy and while breastfeeding, and that the baby should be given probiotics too.

According to the WAO, probiotics aren't likely to cause side effects. But the risk of side effects could be higher in women who have a chronically weak immune system, especially regarding infections that can be caused by the probiotic bacteria.

Every mother can ultimately decide for herself whether or not to take probiotics or give them to her child. This decision may be influenced by things like whether the possible benefit of using probiotics is worth the associated cost and effort. It also often depends on whether the mother has had eczema herself, or whether her other children have had it.

Research on prebiotics

The researchers didn't find any good-quality studies on the possible benefits of taking prebiotic dietary supplements during pregnancy or while breastfeeding. As a result, the WAO does not recommend that women take prebiotics during pregnancy or while breastfeeding.

The researchers found 18 studies on the use of prebiotics in babies. These studies involved only babies and toddlers up to the age of three who were not breastfed. In some of the studies the children came from families with a higher risk of allergies, and in other studies they didn't. Most of the time the prebiotics that were tested in the studies were additives in baby formula.

The studies didn't find any clear proof that prebiotics prevent eczema. The children who took the prebiotics only had a decreased risk of asthma. Due to problems with the way the studies were done and the low number of participants, the researchers rated the quality of the studies as very low. More research is needed in order to be able to reach more reliable conclusions about the pros and cons of prebiotic baby formula. So the WAO makes only a very weak recommendation for the use of prebiotics in infants who are not breastfed.

Sources

• Cuello-Garcia CA, Brożek JL, Fiocchi A, Pawankar R, Yepes-Nuñez JJ, Terracciano L et al. Probiotics for the prevention of allergy: A systematic review and meta-analysis of randomized controlled trials. J Allergy Clin Immunol 2015; 136(4): 952-961. [PubMed: 26044853]
• Cuello-Garcia CA, Fiocchi A, Pawankar R, Yepes-Nuñez JJ, Morgano GP, Zhang Y et al. World Allergy Organization-McMaster University Guidelines for Allergic Disease Prevention (GLAD-P): Prebiotics. World Allergy Organ J 2016; 9: 10. [PMC free article: PMC4772464] [PubMed: 26962387]
• Fiocchi A, Pawankar R, Cuello-Garcia C, Ahn K, Al-Hammadi S, Agarwal A et al. World Allergy Organization-McMaster University Guidelines for Allergic Disease Prevention (GLAD-P): Probiotics. World Allergy Organ J 2015; 8(1): 4. [PMC free article: PMC4307749] [PubMed: 25628773]
• Garcia-Larsen V, Ierodiakonou D, Jarrold K et al. Diet during pregnancy and infancy and risk of allergic or autoimmune disease: A systematic review and meta-analysis. PLoS Med 2018; 15(2): e1002507. [PMC free article: PMC5830033] [PubMed: 29489823]

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