The British Journal of Nutrition published a paper earlier this year showing that University of Florida students taking B. bifidum R0071 daily the weeks before and through exam periods had more days free of cold and flu-like symptoms than those receiving a placebo (Langkamp-Henken et al. 2015).
This study randomized 583 healthy students and allocated them to 4 arms of the study: 3 arms tested a different probiotic strain (B. bifidum R0071, B. infantis R0033 or L. helveticus R0052) and the 4th arm tested a placebo. The daily dose of probiotic was 3×109 cfu for each strain. The study comprised a one-week run in period and a 6-week consumption period. Interestingly, only B. bifidum R0071 showed a positive effect in the primary outcome, which was proportion of healthy days.
This result suggests that this effect may be strain-specific and such a benefit cannot be expected from all probiotic strains. Responses of immune biomarkers to probiotics are known to be strain-specific, as observed in in vitro, ex vivo, animal and human studies (Ashraf and Shah 2014). However, less variability has been observed in results of clinical trials on endpoints such as RTIs with a range of probiotic strains. This discrepancy may be due to (1) that immune biomarkers are not predictive of human immune function, (2) the ability of probiotics to reduce RTIs is not the sole result of immune activity, or (3) limited clinical data prevent us from fully understanding effects. It is noteworthy that a consensus group of experts recently determined that although certain digestive benefits might be considered ‘general probiotic benefits’, that the same could not be said for immune function (Hill et al. 2014).
The strain differences observed may also be due to a low RTI incidence rate. In the control group, students experienced symptoms on only 4% of the days, whereas other studies suggested levels of 10%. Fewer symptoms mean less of a chance for probiotics to demonstrate a benefit. Such is one of the difficulties of studying healthy subjects. It is also possible that individual variability among subjects can confound the ability to sort out positive effects. Understanding the mechanistic basis for clinical effects may enable differentiation of responders from non-responders, allowing researchers to better identify those likely to benefit from probiotic administration (Reid et al. 2010).
This study compliments earlier studies on different probiotic strains showing similar effects. Note two recent systematic reviews with meta-analyses on this use of probiotics for preventing (Hao et al. 2015) and reducing the duration of (King et al. 2014) acute upper respiratory tract infections. Interestingly, although the King et al. review indicated that good quality evidence supported the conclusion that probiotics reduce the duration of illness in healthy children and adults, the Hao et al. review indicated that the quality of evidence was low. Low quality evidence was due in part to the included studies not disclosing randomization and allocation schemes. It is clear in the Langkamp-Henken et al. 2015 study that care was taken to report the trial according to best possible standards.
Take home messages: some probiotics may be able to protect you from cold/flu symptoms, the mechanism for these effects is not clear, and like Langkamp-Henken et al. 2015 study, researchers need to take the time to register, conduct and report probiotic studies properly. Only then will a clear picture of probiotic benefits emerge.