Having three or four cups of coffee a day is not going to do any harm

Spokesman, British Nutrition Foundation

However, there was no evidence that coffee could be connected to anything more than tiny increases in blood pressure.

The report concluded: "Long-term coffee drinking did not substantially increase the risk of developing hypertension.

"Over many years of follow-up, coffee drinking is associated wtih small increases in blood pressure but appears to play a small role in the development of hypertension."

Doctors are keen to control blood pressure because, over time, it can increase the chance of a patient suffering arterial damage which could contribute to heart disease.

Risks

However, in general, the jury is still out on the health risks, if any, of drinking coffee.

Pregnant women in the UK were recently advised to drink no more than four cups a day because of worries that heavy consumption could increase the risk of miscarriage.

A spokesman for the British Nutrition Foundation said: "Having three or four cups of coffee a day is not going to do any harm - unless you are one of the few people who has a predisposition to be sensitive to caffeine.

"In pregnancy, having a couple of cups a day has not been shown to be detrimental."

The caffeine that coffee contains is a stimulant, and in the short term, after drinking coffee, alertness benefits - although once the caffeine "high" has passed, people may become far less alert.

There have also been warnings that coffee may contain chemicals linked to heart attacks and strokes, although no direct link has been established.