Immunomodulatory and Preventive Effects of Olive Leaf Tea Against COVID-19

During the Coronavirus Disease-2019 (COVID-19) pandemic, in addition to the current measures, boosting the immune system seems to be one of preventive measures that can be taken against COVID-19 infection. Various natural agents have been recommended to boost the immune system. The aim of this study was to investigate the possible immunomodulatory and preventive effects of Olive Leaf Tea (OLT) drinking with regards to COVID-19 infection. The study was conducted among 249 workers in a tractor factory where OLT was served. Of the 249 workers, 168 of them were OLT drinkers and 81 were not OLT drinkers. Drinking at least one cup of OLT per day for a minimum of one month was the inclusion criteria used in the study. The workers with a history of infection or vaccination of COVID-19 were excluded. Lymphocyte subsets, IL2, INF-gamma, specific IgM, and IgG levels were analyzed in all the study subjects. The results showed higher values of CD3-/CD16/56 (NK) cells, CD3+/CD16/56 (NKT) cells, total NK (NK+NKT) cells, and serum IFN-gamma and IL-2 levels in OLT drinkers as compared to the nondrinkers. These immune changes are indicative of immune defense mechanisms. Although all the OLT drinkers and non-drinkers reported no history of COVID-19, specific COVID-19 IgG levels were found positive in 60% of OLT drinkers and 38% OLT non-drinkers. There were significant negative correlations between age and NK cells, number of cigarettes smoked and NK cells, number of cigarettes smoked and TNK; and there were positive correlations between OLT drinking frequency and TNF-alpha, IL-2 and IFN-gamma. Also, serum creatinine levels in OLT non-drinkers were found significantly higher than in the OLT drinkers. In conclusion, drinking OLT may contribute fighting against COVID-19 by boosting the innate immune system.