A quantitative comparison of oleuropein and hydroxytyrosol levels in olive leaf extracts on the Australian and North American marketplace.

BACKGROUND
Olive leaf extract, and key constituents including oleuropein and hydroxytyrosol, are generating clinical and research interest as cardiovascular risk modifiers. Positive effects have been reported on blood pressure, immune function, inflammation, and insulin resistance. A range of olive leaf products exist in the Australian and North American marketplace, and they are both self-prescribed by the public and professionally recommended by naturopaths and herbalists.
METHODS
A total of ten olive leaf liquid products were quantified for oleuropein and hydroxytyrosol in an Australian specialist olive chemistry laboratory, using high performance liquid chromatography. Five were Australian practitioner-only liquid extracts, and five were over-the-counter (OTC) liquid extracts, three of which were sold in North America, and two sold in Australia.
RESULTS
Oleuropein concentrations were broadly comparable between Australian and North American OTC olive leaf extracts. Considerable variation in oleuropein content was noted between Australian practitioner-only products, with some demonstrating considerably lower oleuropein levels than over-the-counter products. In four out of five of the Australian practitioner-only products, hydroxytyrosol levels were substantially greater than in any of the Australian or North American OTC products.
CONCLUSION
This research demonstrates broad comparability in oleuropein and hydroxytyrosol concentrations between the selected over-the-counter olive leaf liquid extracts sold in Australia and North America. Similar comparability was not seen between Australian practitioner-only products, and additionally label declarations for oleuropein content were absent. This raises the question for herbal and naturopathic clinicians as to whether clinical results from different olive leaf extracts will be consistent, comparable, or reliable.