The reduction was small but "noteworthy", researchers say

Forty-four people with raised blood pressure were put into two groups. One ate six grams of dark chocolate daily, the other the same amount of white.

The first group saw blood pressure fall slightly, but the others saw no change, researchers wrote in the Journal of American Medicine (JAMA).

The British Heart Foundation warned chocolate was a "treat not treatment".

Fat and sugar

The suggestion that cocoa has health benefits is not new, and previous research had also suggested it could bring down blood pressure.

It is important to remember that chocolate is also high in fat and calories so over-indulgence is not good for your heart British Heart Foundation

This has been attributed to the chemical plant substances known as flavanols which it contains.

However it had been thought that large quantities were needed to achieve the desired effect, and that the benefits would then be offset by the consequences of consuming the high levels of fat and sugar associated with cocoa products.

But researchers at the University Hospital of Cologne say they have now shown that benefits can be achieved with a small amount - 30 calories worth of chocolate.

They looked at 44 people aged between 56 to 73 with either upper-range prehypertension (blood pressure between 130/85 and 139/89) or stage 1 hypertension (between 140/90 and 160/100).

None of those eating dark chocolate registered changes in body weight, or their levels of glucose and lipids.

But their systolic blood pressure - the upper reading which measures the force of blood as the heart beats - fell by 2.9mm, and their diastolic blood pressure - the lower figure taken as the heart relaxes - by 1.9mm.

The researchers noted that the reduction was small, but stressed that the effects were clinically noteworthy. A 3mm reduction in blood pressure could "reduce the relative risk of stroke mortality by 8%, of coronary artery disease by 5%, and of all cause mortality by 4%", they wrote.

They also stressed that asking people to consume a couple of chunks of chocolate a day was far easier than encouraging "complex behavioural changes" to help them reduce their blood pressure.

The British Heart Foundation's nutritionist Sara Stanner said it was "important to remember that chocolate is also high in fat and calories so over-indulgence is not good for your heart.

"Fruits and vegetables provide a range of polyphenols, as well as important vitamins and minerals. Eating five or more portions of fruit and vegetables a day is therefore the best way to protect your heart - and you don't need to worry about over-indulging."