According to an expert, a bar of the sweet treat can slash your risk of heart disease and stroke by 39 per cent.

The Sun has reported that Dr Brian Buijsse believes a 50g treat has the greatest effect.

Buijsse studied nearly 30,000 people aged 35 to 65 in Germany, to reach the conclusion.

Even one small square can help. But if it was increased by 6g, there were 85 fewer heart attacks and strokes per 10,000 people, his eight-year research found.

Dark chocolate containing 70 per cent cocoa is considered best.

"Given the promising health effects of cocoa, it is tempting to indulge in more chocolate. But we should make sure we are eating as part of a healthy and balanced diet," Dr Buijsse said.

He further added, "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." (With Inputs from Agencies)