Background

• Olive leaf extract (OLE) in liquid form is sold both over-the-counter, and to health professionals only for dispensing in their clinics.

• This research aimed to evaluate and compare the chemical profile of different OLE products on the Australian market.

Key Learning Points

• New research showed there was a significant difference in the phytochemical profile of OLE in different products.

• There was a 35-fold variation between the product with the lowest and the product with the highest levels of oleuropein, and an almost 5-fold variation in total biophenols.

• Practitioner-only products were not necessarily stronger than over-the-counter products, and did not make label statements as to the content of any bioactives.

• OLE made from fresh leaves instead of dried leaves tends to have higher oleuropein levels and lower hydroxytyrosol levels.

 

What is Olive Leaf Extract (OLE)?

Olive leaf extract is a herbal medicine derived from the olive leaf, containing an abundance of bioactive compounds. Whilst the main constituents are oleuropein and hydroxytyrosol [1], olive leaf also contains a large number of other biophenols including p-coumaric acid, oleacein, luteolin and many others.

Health Effects of OLE

OLE is a natural antioxidant with a range of pharmacological actions. In-vitro and in-vivo research has shown that OLE has potential antiviral activity, and positively influences various cardiovascular risk factors including inflammation, hypertension, vascular function, and blood lipids [2–5].

In a 2015 clinical trial a 20mL daily dose of OLE standardised to 136mg oleuropein per day reduced daytime and 24hr systolic and diastolic pressures in pre-hypertensive patients, and also reduced plasma total cholesterol, LDL cholesterol and triglycerides [2].

Synergistic Effect of Total Biophenols

Research suggests that the health effects associated with OLE are likely related to bioactives working in a synergistic manner [5,6]. This synergistic effect highlights the importance of comparing total biophenol content, rather than just individual compounds in isolation. Despite this, many products on the market place a sole emphasis specifically on the levels of oleuropein the product contains.

New Australian Research

Our pioneering research compared the broad phytochemical profile of a range OLE products in Australia, and was published in a recent issue of the journal Molecules [7]. This research was funded by the Olive Wellness Institute, and conducted by myself – Ian Breakspear (Senior Lecturer, Endeavour College of Natural Health) – and Claudia Guillaume (Modern Olives Laboratory).

Our research specifically analysed 5 over-the-counter liquid OLE products, and 5 practitioner-only liquid OLE products which are extemporaneously compounded and dispensed by health professionals such as naturopaths and herbalists.

The analysis demonstrated that there was considerable variation in the phytochemical profiles of assessed products. Some key differences between products with the highest and lowest levels of bioactive compounds are listed below:

• Oleuropein (mg/mL): 35-fold variation
• Hydroxytyrosol (mg/mL): 38-fold variation
• Total biophenols (mg/mL): almost 5-fold variation

Figure 1: Comparison of oleuropein, hydroxytyrosol, and total biophenol quantities in parts per million. The grouping on the left (samples A–E) are over-the-counter products, and the grouping on the right (samples F–J) are products for professional extemporaneous compounding and dispensing [7].

What was interesting was that high levels of one bioactive in a product did not always mean high levels of the other bioactives as well. In fact an intriguing trend was observed – products with high oleuropein levels tended to have lower hydroxytyrosol levels, and vice-versa.

Additionally, when the two categories of over-the-counter and practitioner-only produced were compared, the following was observed:

• Over-the-counter products had on average 3 times the oleuropein level of practitioner-only products.
• Practitioner-only products had on average almost 6 times the hydroxytyrosol level of over-the-counter products.
• Average total biophenol content was roughly comparable between the two product categories.

Fresh versus Dry Leaves

Four out of the 5 sampled over-the-counter products – compared to one of the 5 practitioner-only products – were made using fresh olive leaves. Given the observed trend of low oleuropein and high hydroxytyrosol levels in practitioner-only products, the data was examined from the perspective of whether the product was made using fresh or dry leaves.

This showed an even more interesting trend and provided a possible explanation for the low average oleuropein levels in practitioner-only products. OLE made from fresh leaves had on average 3.5 times the oleuropein, and just over a quarter of the hydroxytyrosol level of OLE products made using dried leaves. Oleuropein is known to degrade to produce hydroxytyrosol, and this study indicates that either the drying or storage and transport of dry leaves (or both) is leading to an increased level of this degradation.

Figure 2. Ranges and mean concentrations of oleuropein, hydroxytyrosol, and total biophenols in extracts made from fresh leaf compared to the dry leaf. The vertical coloured bars represent the ranges, and the horizontal labelled white bars represent the means [7]

Limitations of the Research

As stated in the paper, a key limitation of this research was the fact that only one batch of each product was analysed (due to long time periods between individual batch runs particularly in the practitioner-only product space). It is possible that batch to batch variation may reveal other trends, as this is a known issue in herbal medicine [7].

Clinical Takeaways

This research has demonstrated a few issues relevant to the use of OLE in health care.

• Not all OLE products are comparable in terms of chemistry.
• All over-the-counter products made quantitative label declarations for either oleuropein, hydroxytyrosol, or both. None of the practitioner-only products made such declarations, making it impossible for clinicians to determine appropriate dosages in relation to the existing clinical trial data.
• Human studies on OLE for blood pressure control, insulin sensitivity and respiratory infections have utilised OLE preparations standardised between 51-136mg oleuropein per day. At the maximum recommended daily dosage, none of the practitioner-only products provided 51mg oleuropein per day. However 4 out of 5 over-the-counter products provided more than 51mg oleuropein per day at the maximum recommended dose, and 2 of 5 products provided more than 100mg per day.
• It appears that OLE made using fresh leaves has superior oleuropein levels compared to products made using dried leaves.

Access the full paper here

Access study infographic here

References

[1]     Benavente-García O, Castillo J, Lorente J, Ortuño A, Del Rio JA. Antioxidant activity of phenolics extracted from Olea europaea L. leaves. Food Chem 2000;68:457–62. https://doi.org/10.1016/S0308-8146(99)00221-6.

[2]     Lockyer S, Rowland I, Spencer JPE, Yaqoob P, Stonehouse W. Impact of phenolic-rich olive leaf extract on blood pressure, plasma lipids and inflammatory markers: a randomised controlled trial. Eur J Nutr 2017;56:1421–32. https://doi.org/10.1007/s00394-016-1188-y.

[3]     Lockyer S, Corona G, Yaqoob P, Spencer JPE, Rowland I. Secoiridoids delivered as olive leaf extract induce acute improvements in human vascular function and reduction of an inflammatory cytokine: A randomised, double-blind, placebo-controlled, cross-over trial. Br J Nutr 2015;114:75–83. https://doi.org/10.1017/S0007114515001269.

[4]     Perrinjaquet-Moccetti T, Busjahn A, Schmidlin C, Schmidt A, Bradl B, Aydogan C. Food supplementation with an olive (Olea europaea L.) leaf extract reduces blood pressure in borderline hypertensive monozygotic twins. Phyther Res 2008;22:1239–42. https://doi.org/10.1002/ptr.2455.

[5]     Vogel P, Machado IK, Garavaglia J, Zani VT, de Souza D, Dal Bosco SM. Beneficios polifenoles hoja de olivo (Olea europaea L) para la salud humana. Nutr Hosp 2015;31:1427–33. https://doi.org/10.3305/nh.2015.31.3.8400.

[6]     Hashmi MA, Khan A, Hanif M, Farooq U, Perveen S. Traditional uses, phytochemistry, and pharmacology of olea europaea (olive). Evidence-Based Complement Altern Med 2015;2015. https://doi.org/10.1155/2015/541591.

[7]     Breakspear I, Guillaume C. A Quantitative Phytochemical Comparison of Olive Leaf Extracts on the Australian Market. Molecules 2020;25:4099. https://doi.org/10.3390/molecules25184099.

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