Effects of a dietary supplement on the incidence of acute respiratory infections in susceptible adults: a randomized controlled trial

Introduction: although supplementation of specific micronutrients may improve immunologic factors, few studies about the combination of micronutrients with plant extracts on the occurrence of acute respiratory infections (ARI) have been published. Objectives: to assess the effect of a nutritional supplement with micronutrients and plant extracts on the incidence of ARI in susceptible adults between January and April, 2012. Methods: a randomized, double-blind, parallel, placebo- controlled clinical trial was performed. Participants were adults susceptible to ARI who were healthy at the time of evaluation, signed informed consent forms and were not taking medication. They completed a medical history; weight, height, vital signs and laboratory analyses were assessed. Subjects were randomly assigned for consumption of the supplement or a placebo, for a 90 days period. Subjects made daily diary entries indicating the presence ARI symptoms. Those who became ill notified researchers and the attending physician confirmed the presence of an infection. Fisher’s exact test was used to compare the proportion of ill subjects between groups. Relative risk and risk difference were also calculated (p < 0.05 significant). Results: of 59 included subjects, 45 (25 women) completed the study (21 in the supplemented group and 24 in the placebo group). There were no significant differences at baseline between groups. After the intervention, the supplemented group had a lower incidence of ARI compared with the placebo group (57.1% vs. 91.7%, p = 0.013, RR = 0.62, 95%CI 0.42, 0.92). Discussion: the consumption of a supplement with vitamins, minerals and plant extracts may decrease the incidence of ARI in susceptible adults.