Drinking an extra cup or two of coffee can double stroke risk for light coffee drinkers, says a new study. Light coffee drinkers - who drink coffee just once or twice a day - are twice as likely to suffer a brain blood clot if they have an extra cup or two, the study found.

The risk of a potentially fatal stroke was greatest in the hour following consumption. After two hours, coffee's effects had worn off and the risk of a stroke passed, reports the journal Neurology.

But the danger lies in occasional exposure to relatively higher caffeine levels, which made light coffee drinkers more susceptible, according to the Daily Mail.

This could be because coffee-lovers who get through several cups a day become ‘desensitised' to the effects of caffeine, like raised blood pressure, stiffening of arteries and higher norepinephrine levels, a stress hormone that increases heart rate.

Experts at Harvard Medical School in US studied 400 stroke victims, comparing each one's coffee intake in the hour before their stroke with their usual consumption over the previous year. Around one in 10 had consumed coffee less than an hour before falling ill.

he consumption was linked with a risk of stroke in the subsequent hour which was twice as high as during the periods where there was no coffee consumption.

Researchers found no such association with caffeinated tea or cola. The risk was mainly confined to those who exceed their normal intake of a cup or so a day.