MedicalResearch.com: What are the main findings of the study?
Dr. Azad: In this study, our goal was to evaluate the clinical evidence for using probiotics (live “healthy bacteria”) to prevent childhood asthma. We reviewed the results of 20 clinical trials involving over 4000 infants, where probiotics were administered during pregnancy or the first year of life, and found no evidence to support the use of probiotics for asthma prevention. Children receiving probiotics were just as likely to develop asthma as children receiving placebo. Similarly, there was no effect of probiotic supplementation on the development of wheezing.
MedicalResearch.com: Were any of the findings unexpected?
Dr. Azad: Yes, somewhat. We know that gut microbes help ‘educate’ the developing immune system, and that disruption of the gut microbiota is associated with allergic diseases (disorders of the immune system), including asthma. Using probiotcs to promote a healthy gut microbiota has therefore been proposed as a new strategy to prevent allergic disorders. In fact, there is good evidence that probiotics can prevent allergic eczema in young infants. However, our results show that – at least so far – probiotics are not effective in asthma prevention.
MedicalResearch.com: What should clinicians and patients take away from your report?
Dr. Azad: Probiotics cannot be recommended for asthma prevention at this time. Of course, probiotics remain useful for other purposes (for example, they are beneficial for preventing bowel disease among premature infants), but there is currently insufficient evidence to recommend probiotics for asthma prevention.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Dr. Azad: Our findings highlight the need for additional research. While there is currently insufficient evidence to recommend probiotics for asthma prevention, this strategy may still have potential. New studies are needed to address the following:
First, we know relatively little about how probiotics work, and which ones are effective. It will be important to study the infant gut microbiota to better understand how gut microbes contribute to asthma development, in order to develop improved strategies for prevention. This is an objective of our research at the Canadian Healthy Infant Longitudinal Development (CHILD) Study (www.canadianchildstudy.ca).
Second, studies have varied widely in the type, dose and duration of probiotic supplementation (among 20 trials, over 15 probiotic strains were tested, with a 1000-fold range in dose, administered for 1 to 24 months). It is possible that some strains are effective while others are not, or that a single strain may be effective with long-term, but not short-term supplementation. The dose may also be important. These issues need to be addressed in new basic and clinical studies.
Third, most trials were not originally designed to detect asthma, so they did not follow the children long enough to accurately diagnose this condition. Asthma diagnosis is difficult before age 6, and only 5 of 20 trials conducted follow up beyond 6 years. This issue could be addressed by extended follow up of existing studies, or with new long-term trials.
Finally, it is also worth exploring whether probiotics are particularly effective among specific patient groups. For example, one study found that probiotics were especially beneficial among infants delivered by cesarean section (who are known to have a disrupted gut microbiota). Infants receiving antibiotics may also stand to benefit, but more research is needed to establish whether targeting these specific patient groups would impact asthma development.
Azad MB ,Coneys JG ,Kozyrskyj AL ,Field CJ ,Ramsey CD ,Becker AB ,et al. Probiotic supplementation during pregnancy or infancy for the prevention of asthma and wheeze: systematic review and meta-analysis. BMJ 2013;347:f6471