Can Olive Leaf Boost the Immune System?

Can Olive Leaf Boost the Immune System?

Many popular immune defence health supplements (e.g. Bioceuticals ArmaForce and Oriental Botanicals ViraForce) contain Olive Leaf Extract (from Olea europaea). This extract has been traditionally used as a folk remedy for a number of infectious diseases of viral, bacterial and fungal origin; but what does the evidence say about this commonly used herb?

A literature search on PUBMED reveals very little human clinical trial data supporting the use of olive leaf for enhancing immune health; reducing the incidence of viral respiratory infections or ameliorating symptoms of cold and flu.

In fact, only a single randomised control trial has been conducted to assess the effect of olive leaf extract on upper respiratory illness (URI) in high school students. As this was only a small-scale study of 32 high school students engaged in elite sport, it is not possible to extrapolate the results of this study to the general population. The results showed no significant change in incidence of URI in subjects taking olive leaf extract. There was a significant reduction in sick days for females, but nearly double the number of URI sick days for males. 

While there is some evidence to suggest that olive leaf extract might provide beneficial effects on blood pressure and insulin sensitivity, there is a paucity of evidence to recommend supplementation with OLE for the treatment or prevention of upper respiratory tract infections such as common cold or flu.