Men who drink one or two mugs of coffee a day are less likely to suffer from erectile dysfunction, a study has found.

According to NHS data, one mug of instant coffee contains about 100mg of caffeine, while a mug of filter coffee contains about 140mg.

A cup of tea and a can of cola contain 75mg and 40mg, respectively.

Researchers found that men who drank between 85mg and 170mg of caffeine daily were 42 per cent less likely to report impotence than those who drank none.

And those who drank between 171 and 303mg of caffeine were 39 per cent less likely.

Even men who were overweight, obese or had high blood pressure - known risk factors for erectile dysfunction - were less likely to suffer from the problem if they drank the equivalent of one or two mugs a day.

Men with diabetes were not helped by caffeine, however. 

The scientists, from the University of Texas, suggested that caffeine triggers a series of effects that help relax the arteries in the penis, thus increasing blood flow.

They studied data from nearly 4,000 men, and, using 24-hour dietary records, assessed the amount of coffee, tea, fizzy drinks and sports drinks they consumed on average per day. 

Dr David Lopez, lead author of the study, said: ‘Even though we saw a reduction in the prevalence of erectile dysfunction with men who were obese, overweight and hypertensive, that was not true of men with diabetes.

‘Diabetes is one of the strongest risk factors for erectile dysfunction, so this was not surprising.’

Coffee has already been linked to a reduced risk of heart attacks and has been shown to protect against dementia, type 2 diabetes and even skin cancer.

These effects are largely down to the caffeine found naturally in coffee beans.

Coffee also contains a range of antioxidants and plant chemicals that give the drink its characteristic smoky bitterness and smell, as well as healthy properties.