Olive oil with high content in phenolic compounds appears to be beneficial for the heart and may protect cardiovascular health, says a study.

Juan Ruano and other Spanish researchers compared effects of consuming phenol-rich olive oil against olive oil after removing most of its phenol content - considered an antioxidant with anti-inflammatory and anti-clotting properties, BBC's online edition reported.

They tested it on a group of 21 volunteers with high cholesterol - a known heart disease risk factor.

To look at the effect of the diet on the cardiovascular system, the researchers measured the ability of the volunteers' blood vessels to respond to sudden changes in blood flow in the fingers, by inflating and then deflating a blood pressure cuff.

Poor responsiveness to this type of test is considered an early warning sign of cardiovascular disease and can also occur immediately after eating a very high fat meal.

Blood vessel response and function was improved for the first few hours after the high-phenol olive oil meal, according to the study.

This improvement was associated with increased levels of a molecule called nitric oxide, which dilates blood vessels, and reduced levels of oxidative stress.

In comparison, there was no improvement after the low-phenol oil meal.

"This is the first study that shows a direct benefit of olive oil with high content in phenolic compounds on endothelial function in vivo," said a researcher.

"The intake of food high in phenols compounds could improve cardiovascular health and protect the heart."

"However, the study used a small number of people and longer term studies with more people are needed to see if the benefit on endothelial function translates into a reduction in risk of cardiovascular disease," the researcher added.