By Alok Jha

London, May 2. (Guardian News Service): People who regularly take aspirin to ward off strokes in later life could bedoing themselves more harm than good, according to a new study. Researchers have found that the proportion of people over 75 in the UK who have suffered bleeding strokes has jumped ten-fold in the past 25 years, reflecting the increased use of antithrombotic drugs such as aspirin and warfarin.

There are two main types of stroke: one occurs when the blood flow tothe brain is blocked by a clot; the other happens when a blood vesselbursts and bleeds into the brain. Antithrombotic drugs can reduce the riskof strokes and heart attacks in people who are known to be at risk of thediseases, because they thin the blood and lessen the chance of developingblood clots. But thinner blood also raises the risk of bleeding.

Although there is no clear evidence to suggest an overall benefit forhealthy people with a low risk of heart disease or stroke, many choose totake aspirin regularly as an insurance policy for later life.

In the study, Peter Rothwell of Oxford University's department ofclinical neurology, found large numbers of older people suffered frombleeding in the brain when they took antithrombotic drugs.

"There's no doubt that aspirin and warfarin - when indicated - arebeneficial, irrespective of age. But there is a tendency now for people totake aspirin just in case. They don't have a history of vascular disease,but they're keen to take it to prevent stroke. What [our] trials have shownis that there is very little evidence that, if you don't have vasculardisease, aspirin does any good - the risks outweigh the benefits."

In the study, Professor Rothwell examined the causes of almost 1,000 strokesrecorded as part of the Oxford Vascular Study, which ran for four yearsfrom 2002. He compared the results with the causes of a similar number ofstrokes recorded in the Oxford Community Stroke Project, from 1981 to 1986.The results are published in the Lancet Neurology.

"In the earlier study, the majority of haemorrhages occurred in peoplewith evidence of fairly severe high blood pressure before the event," saidProf Rothwell. "What we found now, in the last few years, was that whilesome of the younger people had hypertension as a cause, the vast majorityover 75 didn't have hypertension, or it had been treated years ago."

One key difference was that in the later records large numbers of peoplewere taking antithrombotic drugs regularly. "We had about 50 haemorrhagesin each of the two studies - the use of antithrombotics in patients withhaemorrhages was 4% in the 1980s, versus just over 40% now."

Working out exactly how the antithrombotic drugs affect users will need moreresearch. Prof Rothwell said: "It's probably because of the changes thatoccur with ageing in the very small blood vessels in the brain - they tendto become more prone to bleeding. Aspirin makes you more prone to bleed."