Olive leaf extract: on trial
The Mediterranean diet – featuring a high consumption of olive oil – has long been associated with longevity and health. More recently, olive leaf extract has been making a comeback as a natural remedy, with evidence to suggest an array of health benefits. So how far has olive leaf extract testing gone and is there any chance of seeing it reclassified as a bona-fide pharmaceutical? Abi Millar finds out.
Olive oil has long captured the popular imagination as the bedrock of a healthy diet. Used liberally in the Mediterranean region - where residents famously live longer and healthier lives - this most virtue-laden of 'good fats' has been associated with lower inflammation in the body and a reduction in cardiovascular disease.
While it is important to separate hype from science, the connotations are hard to ignore. As far back as Ancient Egypt, the olive leaf was deemed to have heavenly powers, and was used during the process of mummification. In the Bible, the tree is described as a source of both food and healing: 'The fruit thereof shall be for meat, and the leaf thereof for medicine' (Ezekiel 47:12). A little later, Greek Olympians were crowned with a wreath of olive leaves and Jesus taught his disciples on the Mount of Olives.
Making a comeback
It may therefore come as little surprise that the plant is enjoying a revival. According to a recent report by Transparency Market Research, the global nutraceuticals market is growing at a rate of 7.3% per annum, and is expected to surpass $278bn by 2021. This covers dietary supplements, so-called 'functional foods', and any consumable products that fall in the category between a food and a drug.
The market also covers age-old folk remedies, such as olive leaf extract, that have been rediscovered and appropriated for the modern age. Olive leaf was not entirely abandoned following the dawn of modern medicine. Spanish doctors in the 19th century used it to calm fevers, and 20th century scientists extracted a bitter compound, oleuropein, from the plant.
However, natural remedies gradually fell out of favour as the randomised controlled trial was enshrined as the gold standard for a drug. It is only over the last decade or so that such products have made a comeback, with many consumers seeing 'natural medicines' as a key component of preventative healthcare.
As the user base grows, this raises an important question - are the supposed benefits grounded in science (and therefore worth interrogating as we would a drug), or do they mostly come down to seductive marketing strategies and wishful thinking?
Rashda Ali, general manager of Comvita UK, comes down firmly on the 'science' side. Her company manufactures liquid olive leaf extract and olive leaf extract immune support capsules, which, she points out, are being placed under increased scientific scrutiny.
"Extensive research has shown the benefits of the Mediterranean diet are largely due to the healthy antioxidants derived from the high intake of olive oil, made from olive fruit. But because the active compound is much stronger in the olive plant, the research focus has switched to olive leaf," Ali says.
Comvita's olive leaf extract contains 66mg of oleuropein, alongside eleven other potent phenolics. Oleuropein in particular is believed to have powerful pharmacological properties, and while large-scale trials are admittedly lacking, there is a growing body of research to back up certain claims.
So far, the findings seem to point towards antioxidant and anti-inflammatory effects, blood sugar regulation, and protection against heart disease and nerve damage. What's more, elenolic acid, a component of oleuropein, has been shown to have strong bactericidal, antiviral and antifungal capabilities in vitro.
Some of these properties have been more rigorously assessed than others. For instance, effects on blood pressure were first investigated in 1962, when an Italian scientist recorded lowered hypertension in animals. These results have been corroborated several times since, most notably in June 2015 in a study published by the British Journal of Nutrition. Researchers gave 18 healthy participants an acute dose of Comvita Olive Leaf Extract, and tested their vascular function and inflammatory markers. They noted a 'statistically significant improvement' in both metrics.
The same researchers built on their findings with a 'chronic blood pressure trial', published in the European Journal of Nutrition in March 2016. This time, they administered olive leaf extract to 60 pre-hypertensive subjects over the course of six weeks. The results were positive: supplementation was associated with reductions in blood pressure levels, as well as improvements in cholesterol levels, triglycerides and the inflammatory marker interleukin-8 (IL-8).
The effects on blood sugar have been less widely examined, but a study in 2013 on overweight men showed a 15% improvement in insulin sensitivity over the course of a 30-week trial.
"Olive leaf extract has been clinically proven to regulate blood sugar, blood pressure and cholesterol levels," says Ali. "Comvita Olive Leaf Extract may support those who are prone to these conditions and can be used as a prevention in this area alongside a healthy lifestyle. Research efforts are ongoing and we will be able to release more information to the public once it has been reviewed and published."
A bona-fide drug?
It is worth pointing out that because olive leaf extract is a food supplement, as opposed to a bona-fide pharmaceutical, it is subject to a less stringent definition of what constitutes 'clinical proof'. In order to be reclassified as a drug, it would need to undergo extensive, multi-phase trials for a specific indication.
As a nutraceutical, however, it sits in something of a grey area - while its health benefits have been clinically and anecdotally observed, from a regulatory standpoint it falls under the banner of alternative medicine. Even here, there are strict rules about what a manufacturer can say: in 2014, the European Food Safety Authority determined that Comvita did not have enough evidence to back a claim that olive leaf water extract boosts glucose tolerance.
For now, though, its status may seem appropriate for a plant extract regarded as a catch-all remedy. Generally, its users aren't ill people looking for a cure; they're healthy people looking for a boost, and each individual consumer may be looking to derive different benefits. And while some of these benefits may turn out to be largely placebo-driven, the available evidence does suggest grounds for further study.
For these users, the proposition is clear: a natural remedy rooted in folk wisdom, with some scientific backing to boot. As the evidence base builds up, it will certainly be interesting to see how this ancient panacea fits into a modern paradigm.