Does an aspirin a day keep cancer away?

Could cancer prevention be as simple as taking aspirin?

Since it was invented in Germany in 1897, aspirin has been used to treat a range of medical ailments - from the simple headache, through to inflammation. The possible cardiovascular benefits have also been widely discussed.

More recently, news reports have highlighted studies that have shown that aspirin may be able to prevent some cancers, particularly bowel cancer. But before we add reducing cancer risk to aspirin's credentials, it's important to consider the evidence.

The link between aspirin and cancer was first found when the results of seven trials involving over 23,000 people randomly allocated to be given low dose aspirin to prevent strokes and heart attacks were also monitored for cancer outcomes. Combined, these studies showed a link between aspirin and a 34% reduction in deaths from all cancers and a 54% reduction in gastrointestinal cancer. There were also benefits in terms of oesophageal, lung, pancreatic and prostate cancers. However, the participants had to have been taking aspirin for at least five years to see these benefits.

Interestingly, low doses of aspirin (75mg) seemed to work just as well as higher doses taken each day. Using a low dose, a reduction was also found in cardiovascular deaths. However, there was also an increase in the side effects of aspirin, particularly bleeding both into the bowel and brain.

Three of these studies were followed up over 20 years - where it was shown that after taking aspirin for seven and a half years, there was a 31% decrease in all cancers and a 59% decrease in bowel cancer. These results were questioned however, because cardiovascular disease, not cancer was the focus of the study.

A more recent study was performed to assess cancer risk in a group of people carrying hereditary bowel cancer (Lynch Syndrome), which places them at a high risk of developing bowel and other cancers. The sample group in this study were given two 300mg aspirin tablets daily for at least two years. This study showed a 59% decrease in the incidence of bowel cancer in those patients who had taken aspirin. The incidence of other cancers was also reduced. Another study is underway to examine the optimal dose of aspirin that could be taken to reduce cancer risk.

So do we recommend taking aspirin daily to reduce your cancer risk?

The results so far are impressive - and certainly it would seem reasonable for people at high risk of bowel cancer to talk to their doctor about whether a daily dose of aspirin might be right for them. For the rest of us, who are at a low or moderate cancer risk, we do not yet know how effective aspirin will be, nor how much or how often we would need to take it to realise any cancer benefit.

Although daily low-dose aspirin may be sufficient, it is also not without risk, since major bleeding, although uncommon, can be life-threatening.

We do not recommend anyone using daily aspirin without consulting their doctor.

Last but not least, while the evidence is growing, this new information does not replace the major lifestyle cancer prevention messages.

Stopping smoking, controlling weight including diet and exercise, limiting alcohol and adopting sun protection measures in the summer are the best ways of reducing your cancer risk.

For some people, aspirin may provide a useful cancer preventative measure, but we should all continue to focus on the strategies we know can reduce our cancer risk.