Individualized Supplementation of Immunoactive Micronutrients and Severity of Upper Respiratory Infection Symptoms—A Randomized Intervention Study

Certain micronutrients exhibit immunomodulatory effects. However, no intervention has yet investigated the effect of individualized supplementation on the severity of upper respiratory tract infections (URIs). Therefore, we investigated whether a personalized supplementation moderates the incidence and severity of URI. Selenium, zinc, and vitamin D were measured in dried blood spots from 59 healthy participants. Accordingly, a personalized supplement was provided with or without the respective micronutrients. We used WURSS-21 questionnaires to assess the disease status. The blood values converged during the intervention and micronutrients no longer differed between treated and untreated volunteers at the end of the intervention period. The incidence and severity of the illness did not significantly differ between the groups. However, when analyzing the WURSS-21 scores by the intention to treat, the initially randomized treatment arm revealed a significantly higher score than the placebo arm. Upon acute administration, individualized combinations of selenium, zinc and vitamin D do not reduce the number, or contribute to a milder course of URIs. Therefore, supplementation in acute infectious situations seems questionable. Further studies must address the habitual diet in more detail, to better understand the impact of individual micronutrient status on the prevention of URI.