Probiotics
Probiotics are microorganisms that, when given in sufficient amounts, are beneficial to the host. For example, Lactobacillus bacteria inhibit the growth of harmful bacteria in the intestines and studies have demonstrated that lactobacillus supplements can decrease diarrhea in people taking antibiotics.
Do the benefits of probiotics extend beyond the digestive system? The gut is the interface of the body with a huge number of potential allergens. Gut-associated lymphoid tissue (GALT) is the largest lymphoid tissue in the body. Thus it has been hypothesized that probiotics may alter the presentation of antigens and the immune response generated in response to them. In fact, in animal models, oral probiotics do decrease IgE and cytokines produced in response to specific allergens. Might probiotics alter the immune response to protect infants from eczema or to decrease allergic symptoms?
The efficacy of probiotics to treat or to prevent various allergic conditions have been the subject of several clinical trials. Studies have focused on different probiotic agents including several Lactobacillus and Bifidobacteria species. Results vary with species used, with end point studied, and with study design. Several recent meta-analyses have attempted to make sense of the literature to date.
Allergic Rhinitis:
Dr. Vliagoftis, at the University of Alberta, and his colleagues report that most of 12 randomized control trials studying the effects of probiotics on allergic rhinitis demonstrate encouraging results in terms of probiotics decreasing symptoms, decreasing use of relief medications, and increasing quality of life scores. None of the studies that examined immune modulation as an endpoint, however, showed any difference in immune markers (IgE, cytokines, chemokines) in probiotic versus placebo treated groups. The authors caution that because of the limited number of studies, the broad range in probiotics used, in the outcomes studies, and in the study designs, they cannot suggest that patients consume probiotics as therapy for allergic disease.
Atopic Dermatitis/ Eczema:
Dr. Michail and colleagues in a recent meta-analysis demonstrated only a modest and short term decrease in the scoring of atopic dermatitis symptoms in children receiving probiotics versus placebo. His group detected no difference in effects of Lactobacillus vs Bifidobacterium in the various studies included in their analysis. The largest effect was seen with children who presented initially with the most severe dermatitis. They warn that probiotics often contain cow's milk protein, which may trigger an immunce response in infants who have cow's milk allergies.
In a separate meta-anaylsis, Dr. Lee and colleagues suggest that probiotics may prevent pediatric atopic dermatitis in high risk infants if women with strong family histories of atopic disease are given probiotics prenatally and if treatment is continued in the infants after birth. They state that there is no clear evidence that probiotics are an effective treatment for existing pediatric atopic dermatitis.
A recent Cochrane review did not find evidence that probiotics are effective against eczema. They cannot, however, exclude a benefit based on severity of eczema or specific strain of probiotic. They call for further studies that would stratify severity of disease and examine specific strains of probiotics
Caution:
Caution is warranted in the use of probiotics as in at least one study the probiotic increased sensitivity to food and to inhaled allergens. There are also reports of sepsis and bowel ischemia purportedly due to probiotics. There may be a small but unknown risk of sepsis or bowel ischemia with the use of probiotics, especially in select patients.
The future of probiotics in prevention or treatment of atopy is unclear. We reinforce the call for further research that the authors sited here have made.
References:
Borchers AT, Selmi C, Meyer FJ, Keen CL, Gershwin ME. “Probiotics and immunity.” J Gastroenterol 2009; 44:26–46
Boyle RJ, Bath-Hextall FJ, Leonardi-Bee J, Murrell DF, Tang MLK. "Probiotics for treating eczema (Review)"The Cochrane Library 2009, Issue 1
Lee J, Seto D, Bielory L. “Meta-analysis of clinical trials of probiotics for prevention and treatment of pediatric atopic dermatitis.” J Allergy Clin Immunol. 2008; 121 (1).
Michail SK, Stolfi A, Johnson T, Onady GM. “Efficacy of probiotics in the treatment of pediatric atopic dermatitis: a meta-analysis of randomized controlled trials.” Ann Allergy Asthma Immunol. 2008;101:508–516.
Vliagoftis H, Kouranos V, Betsi G, Falagas M. "Probiotics for the treatment of allergic rhinitis and asthma: systematic review of randomized controlled trials." Ann Allergy Asthma Immunol. 2008;101:570–579.