Chocolate lovers have one more reason to celebrate. It seems that eating just 30 calories a day of dark chocolate a day can help lower blood pressure, without weight gain or other side effects, according to a new study.

Foods made out of cocoa contain cocoa polyphenols, a group of chemical substances found in plants, some of which, such as the flavanols, are believed to be beneficial to health. But it was never known how much cocoa was enough to provide benefits.

Dr. Dirk Taubert of University Hospital of Cologne, Germany, conducted a study on 44 middle-age adults (age 56 through 73 years) with the early stages of high blood pressure.

For 18 weeks, participants ate either 6.3 g per day of dark chocolate, which contained about 30 calories and 30 mg of polyphenols, or white chocolate which contains no cocoa and therefore no polyphenols.

The researchers found that those who ate the dark chocolate saw their average systolic blood pressure drop by 2.9 mm Hg and diastolic BP by 1.9 mm Hg. And those diagnosed with hypertension dropped from 86 per cent to 68 per cent.

What's more, no one experienced any changes in body weight, plasma levels of lipids or glucose levels.

Meanwhile, in the white chocolate group, systolic and diastolic blood pressure remained unchanged.

"Although the magnitude of the BP reduction was small, the effects are clinically noteworthy," the authors write.

"On a population basis, it has been estimated that a 3-mm Hg reduction in systolic BP would reduce the relative risk of stroke mortality by eight per cent, of coronary artery disease mortality by five per cent, and of all-cause mortality by four per cent.

The study results are published in the Journal of the American Medical Association.

The researchers say dark chocolate may be almost as effective at lowering blood pressure as major diet changes, and is a dietary change that is much easier to adhere to.

"Future studies should evaluate the effects of dark chocolate in other populations and evaluate long-term outcomes," the authors conclude.