Healthy people should be encouraged to take a daily dose of aspirin to ward off cancer, according to the leader of a new study highlighting the drug's benefits.
The research shows that long-term use of aspirin significantly reduces the risk of developing major cancers, mostly affecting the digestive tract, and dying from them.
If everyone in the UK aged 50 to 64 took aspirin for 10 years an estimated 130,357 cancer deaths could be avoided over two decades, the study found. A further 9,473 fatal heart attacks would also be prevented.
On the other side of the equation, population-wide aspirin use would be expected to cause just under 18,000 deaths over 20 years, mainly due to internal bleeding and strokes.
However, the scientists believe the scales are tipped firmly towards aspirin when weighing up the risks and benefits of the drug.
Lead researcher Professor Jack Cuzick, head of Queen Mary, University of London's Centre for Cancer Prevention, stopped short of urging GPs to prescribe aspirin to healthy patients but added : "I think they should recommend it."
He revealed that he took a daily low-dose aspirin pill every day "as part of a bedtime ritual".
The research pulled together all the available data from reviews and clinical trials looking at both the good and bad effects of preventative use of aspirin.
Prof Cuzick's team found that taking the drug for 10 years could cut bowel cancer incidence by 35% and deaths by 40%.
Similarly, rates of stomach and oesophageal cancer were reduced by 30% and deaths from these diseases by 35% and 50% respectively.
Aspirin had a weaker impact on non-gastrointestinal cancers. But taking the drug lowered rates of lung and prostate cancer by 5% and 10%, and deaths from both by 15%. It also reduced breast cancer incidence by 10% and mortality by 5%.
While aspirin use cut heart attack risk by 18%, it only led to a 5% reduction in heart attack deaths.
Overall, rates of serious or fatal bleeding in the gut due to the blood-thinning effects of aspirin were very low under the age of 70, but increased sharply after that age.
The drug also raised the risk of peptic ulcer by 30% to 60%, and the chances of dying from a haemorrhagic stroke by 21%.
Prof Cuzick said: "It has long been known that aspirin - one of the cheapest and most common drugs on the market - can protect against certain types of cancer. But until our study, where we analysed all the available evidence, it was unclear whether the pros of taking aspirin outweighed the cons.
"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."
The research, published in the journal Annals of Oncology, covered more than 200 clinical trials and other studies investigating aspirin's anti-cancer effects.
Scientists believe the drug combats cancer both by reducing inflammation and suppressing blood-clotting platelets, which are thought to chaperone cancer cells around the body.
The research suggests that to be effective in preventing or fighting cancer, aspirin has to be taken over a long period - at least five years and ideally 10.
There is no evidence that taking more than the recommended low dose of 75-100 milligrams produces any greater benefit.
Prof Cuzick stressed that because of the possible effects, no-one should take aspirin every day without speaking to their GP first.
Certain people were known to be more at risk from bleeding caused by aspirin. They included smokers, patients taking blood thinning drugs such as warfarin, diabetics, and those infected with Helicobacter pylori, a bacterium linked to gastric ulcers.
That message was echoed by Dr Julie Sharp, head of health information at the charity Cancer Research UK (CRUK), which co-funded the study. She 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 - such as bleeding, stomach ulcers, or even strokes in some people.
"Before aspirin can be recommended for cancer prevention some important questions need to be answered, including what is the best dose and how long people should take it for. And tests need to be developed to predict who is likely to have side effects.
"Given the continued uncertainty over who should take aspirin, Cancer Research UK is funding a number of trials and research projects to make the picture clearer."
Add-Aspirin, a major CRUK-funded trial still in the planning stage, aims to recruit around 10,000 cancer patients who will receive either daily aspirin or a dummy placebo drug over five years.