Taking just quarter of an aspirin tablet a day could slash the risk of bowel cancer by a fifth, a major study has concluded.
Harvard scientists found that middle-aged people who regularly took the painkillers were less likely to be diagnosed with cancer of any kind.
The researchers found that the cheap pills, which cost less than 2p per tablet, are particularly effective at warding off cancers of the digestive system.
The most dramatic impact was seen for bowel cancer, with people who took aspirin every day for six years seeing their risk drop by 19 per cent.
The experts, who tracked 136,000 people for 32 years, predicted that regular aspirin use in the US could prevent 30,000 tumours a year.
If the findings are applied to Britain, 6,000 cases of bowel, stomach, pancreatic, intestinal and oesophageal cancer might be prevented each year.
Experts today said that people with a family history of these cancers should consider regularly taking a low dose of aspirin.
And the Harvard team said that, if combined with screening programmes, use of aspirin could be a cheap and effective way of saving thousands of lives.
Lead author Professor Andrew Chan, a cancer expert at Massachusetts General Hospital, said: ‘It would be very reasonable for individuals to discuss with their physicians the advisability of taking aspirin to prevent gastrointestinal cancer, particularly if they have risk factors such as a family history.’
But he stopped short of advising that everyone start taking the pills, because for some people they can cause side effects including internal bleeding.
His team found that taking aspirin of 81mg a day – roughly a quarter of the standard 300mg tablet – for at least six years saw the risk of cancer of any kind drop by 3 per cent.
Those who took the pills also saw a 15 per cent in risk of gastrointestinal cancers, which include tumours of the gullet, stomach, intestine and pancreas.
And for bowel cancer, which affects 41,000 people in Britain every year, the risk of diagnosis was reduced by 19 per cent.
Professor Chan said: ‘Our findings imply that aspirin use would be expected to prevent a significant number of colorectal [bowel] cancers above and beyond those that would be prevented by screening and may have even greater benefit in settings in which the resources to devote to cancer screening are lacking.
‘But we are not at a point where we can make a general recommendation for overall cancer prevention.’
This is because aspirin in some cases can cause stomach bleeds and ulcers, which are not usually fatal but can require hospital treatment.
People at increased risk of bowel cancer include those with a family history of the disease, the elderly, and those who are overweight, smoke and eat lots of red meat.
The Harvard team analysed data from almost 136,000 participants who were tracked as part of two major US health projects.
The participants, which included women aged at least 30 when they joined the programme, and men aged at least 40, were asked every two years for more than three decades to answer questions about their diet, lifestyle, health and other factors.
The authors found that those who took the equivalent of one ‘baby’ aspirin of 81mg a day had a lower risk of cancer after six years of taking the pills.
Those people who were taking the painkillers did so because of pain from headaches, arthritis or muscle problems, or because their doctor had prescribed the drugs to ward off the risk of cardiovascular disease.
Low-dose, or ‘baby’ aspirin pills are often prescribed to people at risk of heart disease. Sold in tablets containing 75mg to 81mg aspirin, they are roughly a quarter the strength of a standard 300mg tablet sold for pain relief.
Aspirin has been used as a pain killer for thousands of years, since the Ancient Egyptians found that an extract of willow bark helped mothers cope with the pain of child birth.
But in recent years scientists have found that the cheap drug has many more applications.
Because it thins the blood and reduces inflammation, scientists are increasingly finding that it can ward off the threat of diseases including cancer.
The drug is commonly prescribed by doctors in lower doses to prevent heart problems, because it stops platelets in the blood clumping together to form clots.
And because the drug promote blood flow to the pelvis and to thicken the lining of womb, fertility experts are increasingly giving it to women who struggle to conceive.
Scientists have for some time been exploring whether aspirin may also slow the progress of cancer once it has taken hold.
A Dutch study last year found that cancer patients who took aspirin saw their five-year survival rates almost double.
But the new Harvard study provides the strongest evidence to date that aspirin may also be used to stop cancers developing in the first place.
The authors do not know exactly how this works, but they suspect it may be because aspirin reduces levels of an enzyme called cyclo-oxygenase, which promotes the formation of tumours.
Mark Flannagan, chief executive of Beating Bowel Cancer, said: ‘This and previous research has suggested that taking aspirin might reduce your risk of developing bowel cancer.
‘However, we recommend that you consult your GP before undertaking any course of treatment due to the possible side effects.
‘Anyone looking to lower their risk of developing bowel cancer should reduce their intake of red and processed meat, high fat foods and alcohol, and have a healthy diet, take regular exercise and stop smoking.’
Nicola Smith, Cancer Research UK’s senior health information officer, added: ‘This study adds to what we know about the potential for long-term aspirin use to reduce the risk of cancer, particularly bowel cancer, though it didn’t consider the risk of side effects such as internal bleeding.
‘We need to understand more about who would get the best balance of benefits and risks of side effects, how much aspirin they should take, and for how long.’
The research was published in the journal JAMA Oncology. Source: Daily Mail