Objective: A randomized, double-blind, placebo-controlled intervention study was carried out in order to investigate whether consumption of a dietary supplement containing probiotic bacteria plus vitamins and minerals over a period of at least three months in winter/spring affects the duration, frequency, and severity of symptoms of naturally acquired common cold infections as well as cellular immune parameters.
Methods: 477 healthy men and women (aged 36 +/- 13, mean +/- SD) who had not been vaccinated against influenza were randomly assigned to a group who received daily the probiotic multivitamin and mineral supplement (verum) or a placebo, for three (n = 239) or for 5.5 months (n = 238). Cellular immune response was determined in 60 participants per study group by flow cytometry before and after 14 days of supplementation.
Results: The incidence of respiratory tract infections regarded as being virally induced was 13.6% lower in the verum group compared to the placebo group (p = 0.07). During respiratory tract infection episodes, the subjects recorded common cold and influenza-like symptoms daily. All symptoms were reduced in the verum group. We found a relative reduction of 19% in the total symptom score (p = 0.12), 25% in influenza symptoms (p = 0.09), and 54% in the number of days with fever (p = 0.03). The duration of these infections was not affected. Leukocytes, lymphocytes, in particular T-lymphocytes including CD4+ and CD8+ cells, as well as monocytes were significantly higher increased in the verum group, during the first 14 days of supplementation compared to placebo.
Conclusion: These data indicate that the intake of a dietary supplement containing probiotic bacteria plus vitamins and minerals during a period of at least three months in winter/spring may reduce the incidence and the severity of symptoms in common cold infections in otherwise healthy adults. This may be due to stimulated cellular immunity.