Furthermore, there is a need to quantify oleuropein in the growing number of nutritional supplements containing olive leaves, particularly given that some products claim to contain concentrations of oleuropein, as high as 40%. It significant that Breakspear and Guillaume found that nutritional supplements on the Australian market vary substantially in their concentrations of oleuropein, whereas Medina et al found that only 17-26% of polyphenols diffused to the aqueous phases of olive leaf infusions .