Can probiotics or prebiotics prevent or treat respiratory tract infections?

From the common cold right through to the flu, it is something most people are faced with many times over in their life. And all of us could do with less coughing, sore throat, runny nose, body aches and fatigue in our lives. Our gut microbiota plays an important part in our immune system, so scientists for some years have looked at how changing our gut microbiota could influence respiratory tract infections. In this podcast, I’ll look at the current state of play for the role of supplemental probiotics, prebiotics and synbiotics in tackling acute respiratory tract infections.

Links referred to in the podcast

• Systematic review of probiotics, prebiotics, and synbiotics for respiratory tract infections https://pubmed.ncbi.nlm.nih.gov/35948276

Episode transcript
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Transcript

From the common cold right through to the flu, it is something most people are faced with many times over in their life. And all of us could do with less coughing, sore throat, runny nose, body aches and fatigue in our lives. Our gut microbiota plays an important part in our immune system, so scientists for some years have looked at how changing our gut microbiota could influence respiratory tract infections. In this podcast, I’ll look at the current state of play for the role of supplemental probiotics, prebiotics and synbiotics in tackling acute respiratory tract infections.

Respiratory tract infections, defined as illnesses that arise from infections of the sinuses, throat, airways, and lungs, are common and are a leading cause of ill health and death globally. The main cause of acute respiratory tract infections are viruses which include rhinovirus, the coronavirus family which can cause the common cold right through to COVID, and of course the influenza virus.

The classic symptoms of a respiratory tract infection include coughing, sore throat, nasal congestion, runny nose, sneezing, and fever. But in some cases, infections can become life-threatening, especially in people with an underlying health condition or a weakened immune system. Think about the world’s yearly death toll just from influenza.

 Certainly, good nutrition is important for good health and with that, supporting a robust immune system that can help fight off invading pathogens. And I’ve already devoted a podcast episode to the role of certain micronutrients in preventing and treating respiratory tract infections so you can go back to episode 62 titled: “Can micronutrient supplements prevent or treat respiratory tract infections?” to get the full details.

Here’s the summary of that podcast. Vitamin C supplementation shows a small, but significant, effect on reducing the risk of developing respiratory tract infections by 4 percent. The duration of symptoms can also be cut by 9 percent.

And then there is vitamin D which can reduce the risk of developing an infection, but by only a tiny 3 percent with the duration of the infection reduced by 6 percent.

The news on zinc was that it can considerably reduce the duration of respiratory infections by almost half. The effect of zinc on reducing the duration of symptoms is the standout finding when it comes to specific nutrients helping to treat respiratory tract infections.

As for reducing the risk of infection in the first place, none of the nutrients seemed to be standout choices that you would recommend a person to take long-term for a tiny theoretical benefit of reducing the odds of an illness. This is a nice example of where statistical significance does not equate to clinical significance.

Unless you’ve been living under a rock, you’d also know that the gut microbiome is a major player in our health and the functioning of our immune system. So, this is now being looked at for how modulating the gut ecosystem could influence the course of respiratory tract infections. And here we have not only probiotics and prebiotics but also synbiotics which are a combination of the two together and which could be useful for the prevention and/or treatment of respiratory tract infections.

So, let’s jump straight into the evidence base and for that, we have a recently published systematic review and meta-analysis. Thirty-nine randomised controlled trials were included and each examined the effect of supplementation with probiotics, prebiotics, or synbiotics versus a placebo on the incidence, duration, and severity of respiratory tract infections in over 9,000 men and women up to the age of 65 years across all major areas of the globe. And the mix of trials included people with no health conditions, adults who were physically active, and adults with defined chronic health conditions.

Not surprisingly, most of the trials used probiotics as the intervention agent. And these were mostly delivered as single strains of Bifidobacterium, Lactobacillus or Enterococcus, or as multiple-strain products. For trials that used prebiotics, the agents were galacto-oligosaccharides, oat beta-glucans, or xylo-oligosaccharides.

Studies with synbiotics used single-strain or multi-strain probiotics containing Bifidobacterium and/or Lactobacillus combined with galacto-oligosaccharides, fructo-oligosaccharides, or xylo-oligosaccharides. The intervention duration ranged from 3 to 52 weeks. And I’ll link to the review in the show notes. https://pubmed.ncbi.nlm.nih.gov/35948276

So, let’s get on to what the review found. For probiotics, they could show a small beneficial effect on the incidence, duration, and severity of respiratory tract infections. This translated to a 9 percent lower risk of developing an infection in the first place and about a day less of suffering from the infection – that’s nothing to sneeze at. And if anything, these benefits are in the lower range for what has been reported in previous meta-analyses on the topic, which have ranged from an 11  to 47 percent reduction in the risk of experiencing at least one respiratory tract infection and a 0.8- to 2.7-day reduction in the duration of the infection.

Probiotics’ effects were fairly consistent across different strains, doses, and duration of taking the probiotic. So, there could be a general benefit for a range of probiotics here.

Interestingly, the reduction in the duration of the infection seemed to be larger when fermented dairy was the source of the probiotic. This could be because of the fermentation process itself which can increase the bioavailability of immunomodulatory nutrients in milk as well as metabolise nutrients in milk, resulting in the production of a variety of compounds with immunomodulatory properties.

Supplementation with synbiotics had a small beneficial effect on the incidence and duration of respiratory tract infections. But for prebiotics alone, it was hard to draw any conclusions with only three studies that could be analysed in the review.

There was considerable variation in many of the analyses with many trials having a potential or high risk of bias. But because the findings were relatively consistent across the different intervention formulations, doses, and durations then it gives greater substance to the validity of the results.

One caveat is that the benefit of probiotics was not seen in physically active participants. This could be because exercise already has a known beneficial effect on the gut microbiota and immune function, so taking probiotics may not add much more here. And of course, people who keep physically active tend to adopt many other positive health behaviours that can reduce their risk of respiratory tract infections.

So, let’s wrap all this up. Taken together, the available evidence suggests that supplementation with probiotics, especially in the form of fermented dairy, may have a small beneficial effect on reducing the burden of respiratory tract infections in physically inactive adults. If you’re pretty active and healthy to start with, then a probiotic supplement may not give you as much of a benefit outside an insurance policy ‘just in case’, but there is merit to considering that because colds and flu kinda suck.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.