The results of the Eurolive study, published in the Annals of Internal Medicine (Vol. 145, pp. 333-341), may well convince health-conscious consumers to continue to pay more for these benefits, after a drop of 35 per cent for last year's olive crop drove prices up to record highs.
Interest in olive oil, a key part of the Mediterranean diet, has increased significantly in recent years on the back of studies linking the diet to lower incidence of cardiovascular disease (CVD) and certain types of cancer.
Indeed, sales in the UK in 2004 alone were worth £107m (€157m), compared with just £1m (€1.47m) 20 years ago, according to AC Nielsen.
The research, led by Maria-Isabel Covas from the Municipal Institute of Medical Research (IMIM), assigned 200 healthy male volunteers from five European countries - Spain, Denmark, Finland, Italy and Germany - to one of three interventions, replaced their normal dietary fats with olive oils (25 mL) with differing phenolics contents (2.7, 164, or 366 mg/kg) for three weeks. This was followed by a two week washout period, and then cross-over to one of the other interventions.
Blood samples were taken before and after each intervention to measure glucose, plasma lipids, oxidative damage to lipid levels, and antioxidant levels.
Covas and her co-workers observed a linear increase in high-density lipoprotein (HDL) 'good' cholesterol levels was observed relative to the increasing phenolic content of the olive oil, with changes of 0.025, 0.032, and 0.045 mmol/L for the low, medium and high polyphenol-containing olive oils.
The ratio of total cholesterol to HDL cholesterol, reported to be the most specific lipid risk factor for CVD, decreased in a dose-dependent manner for the olive oils for the users by around 0.3 mmol/L after five years.
CVD causes almost 50 per cent of deaths in Europe, and is reported to cost the EU economy an estimated €169bn ($202bn) per year. According to the American Heart Association, 34.2 per cent of Americans (70.1m people) suffered from some form of cardiovascular disease (CVD) in 2002.
Polyphenol dose-dependent decreases were also observed for triglycerides, and oxidative damage to lipid levels.
"Olive oil is more than a monounsaturated fat. Its phenolic content can also provide benefits for plasma lipid levels and oxidative damage," wrote the researchers.
"This study represents a key piece for recommendations [for virgin olive oil ahead of other types of oils] and contributes information with great repercussions for the community, especially in populations or countries where the olive oil does not comprise habitual of the diet," said IMIM in a statement.
The Med diet, rich in cereals, fruits, legumes and whole grains, fish and olive oil, has been linked to longer life, less heart disease, and protection against some cancers. The diet's main nutritional components include beta-carotene, vitamin C, tocopherols, polyphenols, and essential minerals.