The finding supports earlier research that potassium-rich food such as bananas could play a role in controlling blood pressure.

A 1997 study suggested people would have to eat five bananas a day to have half the effect of a blood pressure-controlling pill.

Now researchers in India have reported that blood pressure fell by 10% in people who ate two bananas daily for a week.

Billion-dollar industry

The study involved human volunteers at the Kasturba medical college in Manipal in southern India.

It followed successful experiments in rats that showed that ripe and unripe bananas have compounds that can lower blood pressure.

Current drugs to lower hypertension, or high blood pressure, are called ACE-inhibitors. They are expensive and may produce side-effects such as dizziness.

They inhibit the action of angiotensin converting enzyme (ACE) which is responsible for forming a substance angiotensin-2 that constricts blood vessels and raises the pressure inside them.

The pharmaceutical trade in ACE-inhibitors is worth billions of dollars every year.

The Indian scientists report that natural compounds in bananas act in a manner similar to anti-hypertensive drugs in the Indian medical journal Current Science.

The Manipal team studied six popular banana varieties and found that all had ACE-inhibiting properties, though the ripened bananas had a stronger action than unripe ones.

Earlier studies

The 1997 study was carried out at Johns Hopkins University in the US.

Other foods may also have benefits

Its findings focussed on the role played by potassium, a mineral known as an electrolyte. Potassium works with sodium to help regulate fluid balance.

The study suggested that a daily intake of 2,300 mg of potassium - about five bananas - may lower blood pressure by about half as much as drugs can.

Last August, the American Heart Association advised that people with high blood pressure should eat a diet high in minerals and low in fat.

Researchers on its nutrition committee put a group of 459 people with mild hypertension on three different types of diet over an eight-week period.

The first diet was a control; the second was high in fruit and vegetable and the third was low in fat and high in fruit and vegetables. All three diets were low in salt.

The researchers found that a diet rich in fruit and vegetables alone can reduce diastolic pressure by 1.1mm of mercury.