Curr Opin Allergy Clin Immunol. 2013;13(3):280-286.
Abstract and Introduction
Purpose of review To describe the current literature on clinical trials of probiotics for eczema and food allergy prevention in view of recent new approaches and long-term follow-ups.
Recent findings Attempting allergy prevention by probiotic administration has been most successful when assessing atopic eczema, the most prevalent allergic disease at an early age. More than half of the published studies demonstrate a decrease in eczema prevalence until 2 years, whereas the remaining studies fail to show an effect. Effects have been most consistent with combined prenatal and direct postnatal supplementation of the infant and appear strain-specific, with Lactobacillus rhamnosus most often showing an effect. Prenatal-only and postnatal-only studies often fail to show effects. Recent long-time follow-ups have shown promising but not consistent results. A very recent follow-up of a large well conducted cohort shows that long-term effects of eczema prevention persists until age 4 and prevention of respiratory allergies might also be possible.
Summary Prevention of eczema with probiotics seem to work until age 2 years and extended effects until 4 years have been shown in high-risk for allergy cohorts. Effects are strain-specific, with L. rhamnosus showing the most consistent effects especially when combining pre and postnatal administration.
The increase in allergic diseases has been linked to the relative lack of microbial stimulation, especially in early childhood when the permeability of the gut is higher and the gut immune system is not fully developed. A recent understanding is the coevolution of the human species and the metagenome. The diversity of the microbiome and its contribution to the development of allergic and autoimmune diseases has gained much attention. The body's largest immune system residing in the gut is complexly stimulated by the gut microbiome, which is considered central when evaluating the hygiene hypothesis, now rephrased as the micoflora hypothesis of allergic diseases. New molecular techniques enable broader analysis of microbiota and the microbiome.
Development of oral tolerance requires contacts with microbes.A low diversity of gut microbiota during the first months has been associated with development of atopic eczema. Mice reared in germ-free environments do not develop tolerance, but this can be reconstituted with the administration of bifidobacteria. Further, less lactobacilli and bifidobacteria have been shown in the gastrointestinal tract of infants developing allergy later. This led to the probiotic concept.
Supplementing microbes using probiotics, health-promoting nonpathogenic bacteria in an attempt to prevent allergies is a well tolerated alternative. Twenty-three randomized, placebo-controlled intervention studies regarding the clinical effect of probiotic supplementation on development of allergy and eczema in particular have been published. Eczema is the most prevalent allergic disease in early childhood and fairly easy to diagnose reliably using well defined validated criteria and a reliable marker of allergic disease being a significant risk factor for developing respiratory allergies later. Many studies also report on the prevention of food allergy, but its prevalence is significantly less than that of eczema. Around 60% of the studies show a favourable effect decreasing the risk of eczema during the first years of life. The remaining studies fail to show an effect. Most investigators have chosen high risk for allergy cohorts to study the probiotic preventive capacity. This review highlights recent work on prevention of eczema and food allergy using probiotics. Since the publication of earlier reviews on prevention and treatment of allergic diseases, several large prevention studies have been published that are the focus of this review.