Aspirin seems to offer most protection against cancers of the digestive system

Taking aspirin every day can reduce the chance of developing or dying from bowel and stomach cancers, a review of all available evidence suggests.

And scientists predict if everyone aged 50 and above in the UK took the drug for 10 years, some 122,000 deaths could be prevented over two decades.But they warn aspirin can cause internal bleeding and say medical advice must be sought before using it.The Queen Mary University of London report is in the Annals of Oncology.

Weighing up benefits

Scientists examined some 200 studies investigating the benefits and harms of taking aspirin - an area of continuing medical debate.They found the drug reduced the number of cases and deaths from bowel, stomach and oesophageal cancer by some 30-40%.There was weaker and more variable evidence that the drug reduced deaths from breast, prostate and lung cancer too.And the study found people needed to take the drug for at least five years to see any benefits.Prof Jack Cuzick, at Queen Mary University of London, who led the research, urged all healthy people aged 50 and above to consider taking a small dose (75mg) of the drug every day for a decade.Researchers predicted if 1,000 individuals aged 60 took the drug for 10 years, a further decade later there would be:

16 fewer deaths from cancer

One fewer death from heart attack

Two extra deaths from bleeding

Prof Cuzick, who has been taking aspirin for four years, said: "Whilst there are some serious side-effects that can't be ignored, taking aspirin daily looks to be the most important thing we can do to reduce cancer after stopping smoking and reducing obesity, and will probably be much easier to implement."

Individual risks

They found benefits continued even when people stopped taking the drug, but say it is unclear exactly how long people should use it for.

As the risk of internal bleeding rises as an individual gets older, they suggest a cut-off point of 10 years.

There is still uncertainty whether other doses of the drug could offer more protection.

Aspirin's well known possible side-effects include bleeding in the stomach and the brain.

And while the study suggests 122,000 lives could be saved if everyone in the UK aged 50-64 took the drug, this is balanced against the estimated 18,000 deaths from side-effects.

Experts warn anyone at high risk of bleeding, including people with blood disorders who take blood thinning medication, or are frequent smokers or drinkers, are more likely to suffer these side-effects.

They recommend anyone considering daily medication should speak to their doctors to discuss individual risks.

Dr Julie Sharp, at Cancer Research UK, said: "Aspirin is showing promise in preventing certain types of cancer, but it's vital that we balance this with the complications it can cause.

"Before aspirin can be recommended for cancer prevention, some important questions need to be answered and tests need to be developed to predict who is likely to have side-effects."

Exactly how aspirin protects against cancer is unknown. Scientists suggest it may reduce inflammation or act on blood cells that would otherwise encourage the spread of the disease.