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 allergies 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 tablet and drink form and are sometimes added to dairy products such as yogurt.

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

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

• the mother takes prebiotics or probiotics while pregnant,
• the mother takes prebiotics or probiotics while breastfeeding, or
• the child is given baby food 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 the probiotics were used in combination in most of the studies: The mothers who participated either took probiotics during pregnancy and while breastfeeding, or both the mothers and their babies took the 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 issues unanswered: The different strains of bacteria were examined separately or in combination, for example Lactobacillus rhamnosus and different types of Bifidobacteria. On the basis of 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 infants from families with a higher risk of allergic diseases. There is hardly any research on whether probiotics can also protect people from families with a lower risk of allergies.

The researchers also analyzed possible side effects of probiotics, such as nausea, constipation, diarrhea and rashes. The research shows no higher risk of these types of side effects, but the information on side effects that was reported in the studies was incomplete.

Wold Allergy Organization recommendations on probiotics

Based on the study data, WAO has issued recommendations: They offer limited support for the use of probiotics in pregnant women who are in their final trimester, breastfeeding women and infants. The recommendation is for the prevention of eczema in children who have a genetic predisposition. Children who have this predisposition have at least one parent or sibling with an allergic condition such as hay fever, eczema, asthma or a food allergy.

According to WAO, the risk of side effects from probiotics is probably low. But this risk may be higher in women who have a chronically weak immune system, especially for infections that can be triggered by the probiotic bacteria.

In the end, it is the mother's individual choice of whether or not to take probiotics or give them to her child. This decision may be influenced by whether the cost and trouble of using the products is offset enough by their possible benefit, for example. It also often depends on whether the mother has had eczema herself, or whether her previous children have had it too.

Research on prebiotics

The researchers didn't find any good-quality studies on whether prebiotic dietary supplements can offer benefits during pregnancy or while breastfeeding. As a result, the use of prebiotics during pregnancy or while breastfeeding is not recommended by WAO.

The researchers found 18 studies on the use of prebiotics in infants. These studies involved only infants and toddlers under the age of three who were not breastfed. Some of the studies had children who came from families with a higher risk of allergies, others involved children who didn't have a greater risk. Most of the time the prebiotics that were tested in the studies were additives in baby food.

The studies did not show any clear preventive effect for eczema. The children who took the prebiotics only had a decreased risk of asthma. Due to flaws in methodology and the low number of participants, the researchers rated the quality of the studies as very low. More research is needed for more reliable conclusions on the pros and cons of prebiotic baby food. So WAO has issued 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.
• 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.

• IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

  Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

  Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.