The difference was small, but significant. Study participants who ate the most chocolate, equivalent to about one third of a cup of chocolate chips, reduced their stroke risk by 17pc.
A total of 37,103 Swedish men aged 49 to 75 took part in the study, which recorded 1,995 cases of a first stroke over 10 years.
Previous studies have shown that chocolate may help prevent diabetes, control blood pressure and protect against heart disease.
Healthy antioxidant plant chemicals called flavonoids are thought to explain the health benefits.
Dr Susanna Larsson, from the Karolinska Institute in Stockholm, said: "Interestingly, dark chocolate has previously been associated with heart health benefits, but about 90pc of the chocolate intake in Sweden, including what was consumed in our study, is milk chocolate."
The men who ate the largest quantities consumed a modest 63 grams a week. This is about a third of a cup-full of chocolate chips, or just a little more than a 58g Mars bar.
Put into context, the 17pc risk reduction amounted to 12 fewer strokes per 10,000 participants over 10 years, or 100,000 "person years".