"These findings give further evidence in favour of olive oil consumption to counteract cardiovascular diseases," wrote lead author Roberta Di Benedetto from Italy's National Centre for Food Quality and Risk Assessment.
Olive oil is the centrepiece of the Mediterranean diet - a regime long associated with the reduced risk of disease. Scientific thought links the beneficial consumption of olive oil to its high content of monounsaturated fatty acids (MUFA) and antioxidants such as phenolic compounds, vitamin E and beta-carotene.
The new study, also featuring researchers from Italy's Department of Drug Research and Evaluation, reports that while tyrosol has a weak antioxidant power, it may play a role in protecting and maintaining the antioxidant defences of a cell, but some caution about the results is needed since this was an in vitro laboratory study.
"Although this in vitro study does not necessarily indicate respective in vivo effects, demonstrating that tyrosol… improves the intracellular antioxidant defence systems can have an important nutritional spin-off in favour of olive oil consumption to counteract cardiovascular diseases," wrote Di Benedetto in the journal Nutrition, Metabolism & Cardiovascular Diseases (doi: 10.1016/j.numecd.2006.03.005).
The researchers used J774 A.1 cells and incubated them with LDL-cholesterol under oxidising conditions along with tyrosol or its derivative, hydroxytyrosol, (concentration range 1.5 micromoles per litre to 0.5 millimoles per litre). The extent of oxidation of the LDL-cholesterol was determined by measuring the formation of thiobarbituric acid reactive substance (TBARS).
Di Benedetto reports that the stronger antioxidant, hydroxytyrosol, was found to be rapidly absorbed by the cells, while tyrosol was found to accumulate in the cells over a matter of time.
In the presence of so-called 'bad' cholesterol (LDL), both biophenols were found to inhibit the oxidation of LDL to differing extents - 100 per cent for hydroxytyrosol versus 40 per cent for tyrosol.
Oxidative modification of LDL has been reported to be a major part of the pathogenesis of atherosclerosis, and subsequently heart disease.
Importantly, the biophenols were found to counteract the impairment of the cells' antioxidant defence molecule, glutathione (GSH), which protects cells from toxins such as free radicals.
"The data collected about tyrosol behaviour offer, in our opinion, an important interpretation of its mechanisms of action," said Di Benedetto.
"These findings could indeed explain why tyrosol, a phenolic compound with a chemical structure unsuitable for strong antioxidant activity, has been shown to exert powerful protective effects against oxidative injuries in cell systems.
Identifying a mechanism for a food's health effect is key to confirming its healthy properties and gaining scientific credibility for its consumption as a health food.
The researchers noted that the main criticism levelled against the nutritional significance of extra virgin olive oil biophenols is that their dietary intake from olive oil is generally very low.
"But when the capabilities to spare GSH and reinforce intracellular antioxidant defences are considered, tyrosol showed a high protective effect," they said.
This all adds up, concluded the researchers, to an important alternative view of the nutritional benefits of olive oil consumption to counteract cardiovascular diseases (CVD).
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.