Easter eggs and other chocolate may be good for the heart and lower blood pressure, provide you eat a tiny amount each day and prefer dark rather than milk or white chocolate, a medical journal reported on Wednesday.

Nutritionists in Germany monitored 19,357 adults aged between 35 and 65 for at least a decade, comparing episodes of ill health with their lifestyle.

Those who tucked into the most chocolate (7.5 grammes on average per day, or about one square of a 100g or 3.5-ounce bar) had lower blood pressure and a reduction of 39 percent in the risk of a heart attack or stroke compared with counterparts who ate the least (1.7g).

"To put it in terms of absolute risk, if people in the group eating the least amount of chocolate... increased their chocolate intake by six grammes a day, 85 fewer heart attacks and strokes per 10,000 people could be expected to occur over a period of about 10 years," said lead researcher Brian Buijsse of the German Institute of Human Nutrition.

The paper, published online in the European Heart Journal, says further work is needed to explain why chocolate appears to help the heart.

Previous research has suggested that the answer may lie in complex molecules called flavanols, which recruit the gas nitric oxide to the cells that line the inner walls of blood vessels. Nitric oxide causes smooth muscles to relax, which may lower blood pressure.

Flavanols are found in cocoa - and as there is more cocoa in dark chocolate, this could explain why milk chocolate or white chocolate were found to be less effective, says the paper.

The experts warn anyone tempted to gorge on chocolate as a result of these findings.

For one thing, a 100g (3.5-ounce) slab of dark chocolate contains roughly 500 calories, so you would have to subtract this figure from your daily food intake - or do exercise to burn it up - to avoid weight gain.

"Small amounts of chocolate may help to prevent heart disease, but only if it replaces other energy-dense food, such as snacks, in order to keep body weight stable," said Buijsse.