An aspirin a day keeps the doctor away — or does it? New research has cast doubt on the widely-held belief that low- dose aspirin is an effective way for otherwise healthy middle-aged people to reduce their chances of succumbing to an early stroke or heart attack.

More than a century may have passed since aspirin was discovered but its properties continue to surprise the medical world. Over the last decade studies have suggested that it can protect against a range of illnesses, including miscarriage, dementia and cancer of the bowel and breast, but it is its use in cardiovascular disease that has attracted the most attention.

Anyone who has been to America, where daily low-dose aspirin (75 – 150mg) is taken by millions of people once they hit their mid-40s, could be forgiven for thinking that British doctors are a little backward in their attitudes to this wonder drug. But our more cautious approach, which is mirrored across much of Europe, now seems vindicated by growing evidence that aspirin can have serious side effects , particularly in those who enjoy good health.

Low-dose aspirin exerts its protective effect by reducing the “stickiness” of platelets — a key component in the formation of blood clots. People taking a daily dose are less likely to form clots in narrowed arteries – the major cause of heart attacks and strokes. Indeed, the effect is so powerful that aspirin is one of the first things given to someone who is having a heart attack.

But there is a downside. This same blood- thinning effect means that even very low doses of aspirin can increase the risk of bleeding. At the milder end of the spectrum this may simply mean nosebleeds or having to spend half the morning walking around with bits of tissue paper stuck to your face when you nick yourself shaving, but at the other extreme it can lead to potentially life-threatening stomach and brain haemorrhages.

The trick is to balance the protective effects against the risk of side effects and herein lies the problem in using the drug in otherwise healthy middle-aged individuals. Although taking aspirin may reduce the odds of having a heart attack or stroke, those odds are pretty small in the first place. But the risks from side effects are pretty much the same whatever your age.

Researchers from the University of Oxford looked at 20 major studies reviewing the benefits of daily low-dose aspirin and their findings, published in the latest edition of The Lancet, suggest that while it is of major benefit in people who have already had a stroke or heart attack, the case is not so clear cut in those who have yet to run into trouble. Put simply, in otherwise healthy people, the marginal reduction in their risk of heart attack or stroke needs to be offset against a marginal increase in their risk of a fatal stomach bleed or brain haemorrhage.

This latest study mirrors the findings of Australian researchers who used a computer model to predict the outcome of a non-selective age-based approach to recommending daily aspirin. Their results suggested that if 20,000 elderly people took the drug over a long period, it would prevent 700 heart attacks and 55 strokes, but the benefits would be offset by over 1,000 stomach bleeds and 130 brain haemorrhages. And the risk benefit ratio is likely to be even worse in younger people.

So what should you do if you are currently taking aspirin? If you are self- medicating because you believe that everyone over 45 should be on aspirin, then I would urge you to stop. And that applies to people who take it before long-haul flights to protect against deep vein thrombosis (DVT) — it is unlikely to prevent a fatal clot but will increase the chances of bleeding in your gut or brain.

If, however, you have been put on aspirin by your GP, particularly if you have had a stroke or heart attack, then you must continue to take it. The benefits in cases like these far outweigh the risks.

The difficulty lies in the grey area in between — healthy people who have other factors, such as high blood pressure, that put them at increased risk of a stroke or heart attack. The case for aspirin is less clear cut here and should be assessed on an individual basis. And this is why it is important not to self-medicate because GPs don’t take just cardiovascular risk into consideration but the other factors that can skew the risk benefit ratio in favour of risk.

The groups below are most prone to side effects.

Heavy drinkers and anyone taking anti-inflammatory drugs such as diclofenac or ibuprofen or modern Prozac-type antidepressants (all of which irritate the lining of the stomach increasing the risk of serious bleeds).

Anyone with a previous history of severe indigestion, stomach ulcers or past stomach haemorrhages.

Anyone with poorly controlled high blood pressure (readings above 150/90). Although low-dose aspirin is routinely used in people with this problem, it should not be started until the blood pressure is under control as it may, paradoxically, increase the risk of stroke.

Anyone about to undergo surgery — aspirin should generally be stopped ten days before an operation to reduce the likelihood of troublesome bleeding.

People with asthma, in whom it can aggravate cough and wheeze Patients taking the anticoagulant warfarin.

Anyone with a suspected aspirin allergy.

For more details on the findings of the Oxford University aspirin study visit:

www.thelancet.com