Image caption Two chunks of dark chocolate should do it

There may be good news for people looking for an excuse to munch on a couple of squares of chocolate after a review showed the treat could reduce blood pressure.

An analysis of 20 studies showed that eating dark chocolate daily resulted in a slight reduction in blood pressure.

The Cochrane Group's report said chemicals in cocoa, chocolate's key ingredient, relaxed blood vessels.

However, there are healthier ways of lowering blood pressure.

The theory is that cocoa contains flavanols which produce a chemical in the body called nitric oxide. This 'relaxes' blood vessels making it easier for blood to pass through them, lowering the blood pressure.

The 100g of chocolate that had to be consumed daily in a number of the studies would also come with 500 calories - that's a quarter of a woman's recommended daily intake Victoria Taylor , British Heart Foundation

However, studies have thrown up mixed results. The Cochrane analysis combined previous studies to see if there was really an effect.

There was a huge range in the amount of cocoa consumed, from 3g to 105g a day, by each participant. However, the overall picture was a small reduction in blood pressure.

A systolic blood pressure under 120mmHg (millimetres of mercury) is considered normal. Cocoa resulted in a 2-3mmHg reduction in blood pressure. However, the length of the trials was only two weeks so the longer term effects are unknown.

Lead researcher Karin Ried, from the National Institute of Integrative Medicine in Melbourne, Australia, said: "Although we don't yet have evidence for any sustained decrease in blood pressure, the small reduction we saw over the short term might complement other treatment options and might contribute to reducing the risk of cardiovascular disease."

High blood pressure is both common and deadly. It has been linked to 54% of strokes worldwide and 47% of cases of coronary heart disease.

However, chocolate packs plenty of fat and sugar as well as cocoa so is not the ideal way of lowering blood pressure.

Dark or milk?

There has also been a warning in the Lancet medical journal that dark chocolate may contain fewer flavanols than you might think. Dark chocolate contains a higher cocoa count than milk chocolate so should contain more flavanols, however, they can also be removed as they have a bitter taste.

Victoria Taylor, of the British Heart Foundation, said: "It's difficult to tell exactly what sort of quantities of flavanol-rich cocoa would be needed to observe a beneficial effect and the best way for people to obtain it.

"With most of the studies carried out over a short period of time it's also not possible to know for sure whether the benefits could be sustained in the long term. The 100g of chocolate that had to be consumed daily in a number of the studies would also come with 500 calories - that's a quarter of a woman's recommended daily intake.

"Beans, apricots, blackberries and apples also contain flavanols and, while containing lower amounts than in cocoa, they won't come with the unhealthy extras found in chocolate."