Hardly a week goes by without media reports of aspirin expanding its repertoire. You could easily think it is the latest wonder drug, but it is available from garages, newsagent's and supermarkets. Research already shows it can reduce the likelihood of strokes, heart attacks and the risk of cancers, while last week Nature magazine reported that it could treat turban tumours, a rare, inherited form of skin cancer.
So should we all take one a day? That's what Professor Nick Wald from the University of London suggested in the British Medical Journal in June. He argued that if the over-55s took aspirin as part of a "polypill" with other drugs (such as those to lower blood pressure) it would have a major health impact on the west. Aspirin may be cheap, and you do not need a prescription for it, but it is still a powerful drug. And, like any medicine, it has risks as well as benefits.
Two days after the Nature report, the BMJ published research showing that aspirin increased the risk of miscarriage when taken by pregnant women. The risk was highest when aspirin was taken at the time of conception. In the study, 1,055 women in San Francisco who had positive pregnancy tests were asked about their use of nonsteroidal anti-inflammatory drugs - types of painkillers that include aspirin - as well as about known risks for miscarriage. Women who had taken these drugs had almost double the risk of miscarriage compared to women who had not taken them.
The study shows only that aspirin is associated with miscarriage, not that it definitely causes it. But Dr Li De-Kun, an epidemiologist at the Kaiser Foundation Research Institute and one of the authors of the study, believes that women should discuss the results with their doctors.
"At this point, it is still a matter for personal choice," he says. "Women who are planning on pregnancy or who are already pregnant, or even women who are sexually active and not planning on pregnancy might want to consider if they should take aspirin. If they occasionally take it for headaches or muscle pain, I would suggest they seriously think about either stopping it or switching to paracetamol which is not associated with a risk of miscarriage."
Professor John Cleland, cardiologist at the University of Hull, believes that we know little about what happens in the first few days in the life of a foetus. "Aspirin could block some powerful developmental pathways," he says. "This is a particularly critical time. It could interfere with the growth of blood vessels in the baby. Aspirin may cause miscarriage because it stops the egg sticking on to the inside of the womb. Until the egg does that it can't grow into a baby. Prostaglandins are chemicals that are important for this stickiness and aspirin may interfere with their production."
Cleland believes that we may have embraced aspirin as a wonder drug too uncritically. "The idea that aspirin is cheap and harmless is one that is beginning to evaporate," he says. "If you take aspirin, there is a risk of kidney failure, ulcers [in the gut] and it is one of the commonest causes of major bleeding from the gut. If you add the total health bill up from these side effects it could be quite a lot."
Aspirin is recommended for people who have already had a stroke or heart attack to prevent them having further attacks and is also used to treat heart failure.
"Doctors should be really conservative about what they recommend in clinical practice," says Cleland. "I would not give it routinely to my patients. I would give it to people for the first six weeks after a heart attack because there are robust clinical trials that show it reduces further heart attacks. Some cardiologists have concerns about the evidence that aspirin can prevent first heart attacks or strokes."
In people with heart failure, Cleland is concerned that aspirin may counteract the proven and beneficial effects of drugs called ace inhibitors that major clinical trials show reduce the risk of death and hospitalisation.
"Ace inhibitors build up defences in the vessel wall against blood clots - these defences are prostacyclins, which lubricate the vessel wall and stop clots sticking to it. Aspirin seems to knock these defences out. We need a more public debate and not a conspiracy of silence on balance. In some people with heart failure it may be harmful."
Joe Collier, professor of medicines policy at St George's Hospital, London, is sure that whatever doubts there are about aspirin, it has been an enormous life-saver. "I am sure that low-dose aspirin has saved millions of lives by stopping second heart attacks and strokes," he says, pointing out that there is not evidence for lots of things. "There is almost no evidence that walking sticks are useful in arthritis."
What interests him most about the aspirin story is how it has taken the medical profession 100 years to begin to use aspirin to its full potential. "It is quite contrary to drug companies pushing through a drug and then replacing it, because the patent runs out - you never get to know the product fully. We are gradually learning about drugs such as aspirin, and morphine and water tablets. You can now use morphine in self-delivery systems that patients can use themselves, and we now know that we can use water tablets in very low doses, without side effects, for high blood pressure. These drugs become your friend and you become able to use them better and better."
At Cancer Research UK, they are feeling increasingly friendly towards aspirin. "There are lots of observational studies looking at why some groups of people get cancer and some do not," says Dr Richard Sullivan, head of Clinical Programmes at Cancer Research UK.
"A paper published in the British Journal of Cancer showed that aspirin could dramatically reduce the risk of cancers of the mouth, throat and gullet. People who took aspirin for at least five years, regularly (probably weekly) had their risk reduced by a third. Smoking and drinking habits, both of which increase the risk for these cancers were taken into account in the analysis."
A trial of more than 1,000 people at increased risk of bowel cancer because they once had pre-cancerous growths - called adenomas - was published in the New England Journal of Medicine in March. The study randomly gave them either aspirin, in low and higher doses, or a placebo. Aspirin reduced the risk of further adenomas after one year by up to 19%. The low dose was the most effective. "This is the gold standard of studies - this is where we start believing," says Sullivan.
How does aspirin stop cancer cells growing? "There is a protein, called Cox-2, on the surface of cancer cells," explains Sullivan. This protein, he says, is part of normal inflammation, and cancer cells cause inflammation. Some forms of cancer cells have much more Cox-2 on their surface than normal cells. Aspirin binds to this protein and inhibits it.
"Cox-2 is also present in breast cancer," says Sullivan. "My personal theory is that aspirin will be most useful in preventing cancers coming back, and aspirin is less toxic than many long-term chemotherapy drugs."
The latest claim for aspirin's benefits - that it can treat an inherited skin condition called turban tumour syndrome - is published in a letter in this week's Nature magazine. The researchers include a team from Cancer Research UK and, again, aspirin is thought to work by being able to damp down the over-active inflammation that encourages the tumour to grow. Proper trials are needed to see if aspirin, applied as a gel to these skin tumours, will shrink them.
But Sullivan warns against people thinking that by taking aspirin they will ward off cancer. "For the average person to prevent cancer, it is not rocket science - if you smoke or if you are obese, then these are the risk factors to worry about," he says.
"If you smoke and drink and take aspirin, the aspirin can't prevent throat and gullet cancer - it may delay it."
Sullivan doesn't take aspirin himself and believes there are analogies with hormone replacement therapy. "HRT was sold as the great panacea but has been a real lesson for us in learning the long-term side effects of a drug [it had been linked with an increase in breast cancer and heart disease in women already at high risk of heart problems].
"Anything you swallow has side effects and you should swallow as few things as possible to give yourself a healthy life. I don't think you should throw aspirin out to the general public at large. You should direct it to people who really need it, where the evidence shows it reduces risk."
