Date Published: October 31, 2013
Publisher: AIMS Press
Author(s): Gareth Morgan.
The clinical use of aspirin, first synthesized over 100 years ago, entered a new phase in 1974 with the reporting of the first randomised trial showing a reduction in vascular disease deaths from low-doses. More recent evidence suggests that the medicine is effective against cancer, which makes aspirin of very considerable potential importance to public health improvement and potentially also to clinical practice. It appears that prophylactic aspirin is being increasingly used throughout the community. There is need therefore for the risks and benefits of low-dose aspirin, and its’ role within healthcare and within public health, to be widely discussed not least as media reports are bringing this issue into the public domain. It also follows that policy decisions need to be taken as to whether or not its use should be actively promoted. In particular, it is important that Doctors and healthcare practitioners are well informed of the risks and benefits so that they can impart this knowledge during consultations. Furthermore, it is important that low-dose aspirin is not perceived as a substitute for a healthy lifestyle, but that it is recommended and uptake monitored alongside other protective behaviours to improve on health gain, such as smoking cessation, moderate alcohol intake, exercise and diet.
Aspirin is an inexpensive, easily available, well-known and widely used medicine. Many households will have this medicine or products containing it, such as is the versatility of aspirin in treating pain, inflammation and fever. The medicine also has other benefits, including the reduced risk of vascular disease and emerging evidence supports a role in cancer prevention. The benefits, however, also need to be balanced against the risks of bleeding caused by aspirin and set in the context of other measures to improve health and reduce disease risk.
Low-dose aspirin prophylaxis, 75-150 mg per day, is now accepted for all those who have clinical evidence of vascular disease, together with those individuals who have a raised vascular risk score . However, there is evidence of considerable under-use of aspirin prophylaxis in such patients , due to both poor compliance and undesirable effects of aspirin. Boosting the use of aspirin prophylaxis in those who have been recommended the medicine by a healthcare professional could yield population benefit by reducing the number heart attacks and ischemic strokes . As will be discussed later, aspirin reduces the risk of ischemic strokes caused by clots but increases the risk of those strokes caused by bleeding.
Evidence from many sources which suggested a reduction in cancer  has now been supplemented by the results from patient data from long-term follow-up of twenty-five thousand individuals who had participated in early randomised trials of vascular protection by aspirin ,. Analyses on an “intention to treat” basis of data from eight trials showed that starting about five years after daily low-dose aspirin had commenced, there was a reduction of one third in all cancer (Hazard ratio (HR) 0.66; 95% confidence limits (CI) 0.50, 0.87) and a 10% reduction in all-cause deaths. The reductions were maintained 20 years later in three trials which had adequate data and benefit increased with duration of aspirin taking and also with increasing age. This finding has important and far-reaching public health implications, not least due to the challenging financial pressures on healthcare systems and the increasing demands related in part to the ageing population. Further evidence of benefit comes from an ad hoc trial of aspirin given to patients with Lynch syndrome, the major form of hereditary bowel cancer . Patients who had completed two years on aspirin had a relative reduction (RR) in incident bowel cancer (RR 0.37; 0.18, 0.78) and other cancers. As well as these studies, which do not give final answers, from the general population and genetically predisposed individuals, there is also evidence aspirin might be used as an adjunct treatment of cancer . This suggests aspirin might be exerting effects on a wide range of cancer pathways and at a variety of stages in the carcinogenic pathway. There remain questions to be answered but the potential public gain is considerable from appropriate aspirin usage.
In six primary randomised trials , the risk of death from gastrointestinal bleeding in the subjects receiving aspirin (4 per 100,000 subjects per year) was almost identical to that in subjects who had been allocated to placebo (5 per 100,000 per year). The report of a previously cited meta-analysis , based on 660,000 follow up years, states: “…there were actually fewer fatal bleeds in participants allocated to aspirin than in the controls (nine vs twenty)”.
One of the challenges in converting the public health potential of aspirin into a reality is to boost the under-use of the medicine in those individuals with a history of vascular events. Whilst acknowledging the wider use of medication compliance, this discreet situation could be improved by strategies such as information campaigns and perhaps supporting those individuals with a history of a vascular event with self-management strategies. On the basis of vascular risk alone, recommendations have been made  and challenged  that regular aspirin taking be considered by subjects over the age of about 50 years. Others suggest that the benefits of aspirin on cancer risk ‘will tip the balance in favour of treatment’ of healthy older subjects and they recommend aspirin from the age of about 45 years ,. On the other hand, the evidence available at present is inadequate to fix an upper age limit for vascular or cancer prophylaxis and it seems unfortunate that estimates of the likely risks and benefits in people of advanced years are based on results of trials which included few elderly subjects. This situation remains a strongly debated issue.
Low-dose aspirin is preventive, both against vascular disease and against cancer. It is not treatment and should perhaps be considered alongside the healthy behaviours. If low-dose aspirin is promoted within the context of the preservation of health, the risks and benefits should be clearly explained so that individuals are enabled to make informed decisions about the protection of their own health. It should be noted, however, that there may be unintended consequences of wider aspirin use, namely individuals do not make other lifestyle changes. There may be an opportunity to therefore re-brand aspirin for primary prevention is ways similar to the taking of vitamins.
Low-dose prophylactic aspirin raises important questions on public health policy: