By: Erik K.
Since its appearance early this year, the novel H1N1 strain of influenza has garnered a large amount of attention from both research scientists and the general media. Recently, the Centers for Disease Control released a projection that, in a worst-case scenario, the virus could affect up to 40% of the US workforce (including those who contract the virus and those staying home to care for the ill). The CDC also predicts that, in this situation, anywhere between 90,000 and "several hundred thousand" Americans could die of novel H1N1 influenza infection or flu-related illnesses (1) Of course, I am assuming that “worst-case scenario” means catastrophic vaccine failure or a major mutation in the virus. Recently, I have run across a number of internet rumors that a homeopathic solution to reduce the severity of the H1N1 pandemic may be the use of probiotics. Being the ever doubtful nutritional immunology researcher, I decided to delve into this rumor to see if there was any truth to the matter.
First of all, I think that I need to define the terms probiotic and probiotic food. In this case, I'll be using a broad definition proposed by the FAO/WHO in 2001 stating that probiotics are “live microorganisms which, when administered in adequate amounts, confer a health benefit to the host” (2). Taking this definition for probiotic, then a probiotic food could be defined as those foods which contain adequate amounts of living, probiotic microorganisms in an adequate environment to confer a health benefit following consumption. There are a large number of “probiotic” foods on the market with a majority of the probiotic microorganisms belonging to the genera Lactobacillus and Bifidobacterium, which are gram-positive lactic acid-producing bacteria that constitute a major part of the normal human intestinal flora (3).
Now, you are probably asking yourself, can eating microorganisms (ie: bacteria) boost my immune system? Indeed, it seems that probiotic microorganisms and their components have been shown to have some immunomodulatory effects. Probiotics have been shown to stimulate T cell proliferation as well as stimulate natural killer cells and macrophages, increase antiviral cytokine release and shift the immune balance towards a Th1 response in in vitro and in animal models; however, this may only be indications to their beneficial effects. These results have been replicated, at least, in part, in human trials (Reviewed in 4-7).
So, hypothetically, probiotics may be able to boost the immune system to help fight off a viral infection. However, here is where we run into a major problem. Stimulation of the immune system itself does NOT imply a positive health benefit for a specific virus. To be able to say that requires clearly defined, controlled clinical trials showing therapeutic effects of probiotics against a specific infection. The few studies I found looking at viral respiratory tract infections (eg: common cold, influenza) did show some promising reduction in the severity and duration of illness and even promoting vaccine response; however, to date these have been smaller trails in select populations using particular strains of probiotics (8-10). What we have to remember is that judging the effect of a probiotic food is extremely difficult. The proof that a probiotic component of a food is beneficial is only valid for the strain with which the study has been performed. Indeed, the benefit may only be considered beneficial for that specific strain, at those specific absolute numbers, in that specific composition and physical state in that specific target group (3).
Don't get me wrong. I think we can all agree that a dietary supplement which could help reduce the severity of novel H1N1 infection would be greatly beneficial to society. I do think that probiotic supplements can eventually be used for immunomodulatory effects. In fact, some probiotics may be perfect candidates for prevention and/or treatment of common respiratory tract infections in certain populations. I'm just skeptical that these results are generalizable to the world population. Even more worrisome is the lack of data on overdosage or long-term consequences of ingesting these microorganisms. Further studies need to be conducted to determine specific groups where these supplements are beneficial. Until then, keep living a healthy lifestyle, eat a balanced diet and get vaccinated.