A quantitative phytochemical comparison of olive leaf extracts.

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[1], blood lipids[2], inflammation[3], and oxidative change[4]. 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 twelve olive leaf liquid products were quantified for oleuropein, hydroxytyrosol and total biophenols in an Australian specialist olive chemistry laboratory, using high performance liquid chromatography. Five extracts were Australian practitioner-only liquid extracts, five were Australian over-the-counter (OTC) liquid extracts, and two were North American OTC extracts.

Results
Oleuropein concentrations in Australian OTC products were on average 53% higher than North American OTC products and 143% higher than Australian practitioner products. Extracts made from fresh leaf contained on average 3.8 times higher oleuropein and 6.5 times lower hydroxytyrosol levels than dry leaf extracts, but had comparable total biophenol concentrations. Only one North American OTC product did not meet constituent label claims, with Australian practitioner products not making any label claims.

Conclusion
Significant variability was observed in the chemistry of various olive leaf extracts. This raises the question for naturopathic and herbal clinicians as to whether clinical trial results can be translated to practice, and whether clinical outcomes from different olive leaf extracts will be consistent, comparable, or reliable.