The Lund University trial built on other studies using Probi’s Defendum proprietary probiotic blend, but here the key difference was a population highly prone to catching the common cold – the world’s most common infectious disease.
Adults typically average 1-3 colds per year, children 4-6 – here the sample of about 900 otherwise healthy 18-70-year-old Germans had caught at least four physician-validated colds in a 12-month period before each of the three winter seasons of the trial.
Two equal-sized groups were given either Probi Defendum (1 billion colony forming units (CFU)) or placebo once daily for 12 winter weeks in the double blind randomised, placebo-controlled trial.
The Lund University researchers were primarily interested to know if the Defendum blend reduced the severity of the colds among the cold-prone but it was the secondary target – the incidence of colds that was supported by the data.
Over the 3-month winter period the Defendum group reported an average of 1.24 colds versus 1.36 colds in the placebo group.
Among those reporting at least one cold, only 20.8% then caught another cold in the probiotic group, compared to 29.8% in the placebo group.
The researchers said probiotic intake “reduced the frequency of recurrent cold infections and resulted in a significantly lower mean number of colds in the participants with colds”.
Participants were determined to be cold-free if they demonstrated no symptoms for two consecutive days. Symptoms included nasal discharge (runny nose); nasal obstruction (plugged or congested nose); sneezing, or sore (scratchy) throat.
The hunt for mechanisms of action
The Probi-funded study, designed by Berlin-based contract research organisation (CRO) analyze&realize, and published in the Journal of Nutrition, sought to demonstrate mechanisms of action via analysis but this endpoint was not validated after scrutiny of immune system biomarkers like IFN-γ, TNF-α, fractalkine, IP-10, TRAIL, IFN-α2a and IL-2Rα.
“The probiotic benefit against infectious diseases can be supported by various mechanisms, either direct, such as competitive exclusion of the infectious agent from mucosal sites, or indirect, such as modulation of the immune response to the infection,” they wrote.
Changes in IFN-γ and fractalkine levels led the researchers to speculate about, “a trend in the probiotic group for proinflammatory priming of the immune system by fractalkine and a balancing effect of this activity from IFN-γ.”
These shifts only occurred after a full 12 weeks of probiotic supplementation, and not after two weeks.
“However, the exact mechanism underlying the probiotic efficacy and the understanding of what parameters may impact this remain to be untangled.”
Grounds for variation
Referencing the body of work linking probiotic strains with upper respiratory tract infections *URTIs) like common colds, they noted, “there are variations among strains with regard to their immunomodulatory capacity and that there are aspects, such as the dose and the length of intervention, that may impact the results. Moreover, seasonal factors may also undermine the interpretation of the data obtained.”
A 2014 meta-analysis of 20 studies linking probiotics and common colds found that, “with the addition of live lactobacilli and bifidobacteria to your diet, the duration of upper respiratory tract infections (e.g. colds) could be shortened.”
There are around 200 viruses and rhinoviruses responsible for causing common colds, for which no universal vaccine exists.
Source: The Journal of Nutrition
Irini Lazou Ahren, Magnus Hillman, Elisabet Arvidsson Nordstrom, Niklas Larsson, Titti Martinsson Niskanen
‘Fewer Community-Acquired Colds with Daily Consumption of Lactiplantibacillus plantarum HEAL9 and Lacticaseibacillus paracasei 8700:2. A Randomized, Placebo-Controlled Clinical Trial’