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Healthy don't need daily asprin PDF Print Email
Taking asprin everyday if you are healthy in the hope of preventing a heart attack or stroke may be doing more harm than good.
It is also claimed that healthy people who take a low dose of aspirin daily also increase theof likelihood of major internal bleeding.

The news is based on a study of nearly 30,000 men and women aged between 50 and 75 without known heart disease. It found that taking 100mg of aspirin everyday almost doubled the risk of serious internal bleeding compared to dummy pills (placebo), while having no effect on heart attacks or strokes.

This respected study suggests that the risks and benefits of aspirin in this group of patients at low risk of vascular disease are small. It is possible that the risks outweigh the benefits but neither outcome reached statistical significance. Other groups of patients at higher vascular risk, like those with high blood pressure, cholesterol or diabetes, may benefit from aspirin. Anyone taking aspirin following a heart attack or stroke should continue to do so as instructed.

 
Who conducted the research?

This research was carried out by F. Gerald R. Fowkes and colleagues for the Aspirin for Asymptomatic Atherosclerosis Trialists. The study was funded by the British Heart Foundation and the Chief Scientist’s Office in Scotland. The the aspirin, placebo tablets and funds for packaging, dispensing, and some statistical analysis was all provided by Bayer Healthcare.

The study was peer-reviewed and published in the Journal of the American Medical Association.

The research tested the effectiveness of aspirin at preventing cardiovascular events in people who were thought to be at risk of atherosclerosis and cardiovascular events highlighted by screening. The study, a double-blind randomised controlled trial, was carried out from 1998 to 2008 in Scotland. The research wanted to identify both good and bad outcomes. Initially they set out to see if fatal or non-fatal heart attacks, strokes or deaths were reduced by aspirin, but they also monitored the group for side effects, such as bleeding.


What was involved?

The screening consisted of the ankle brachial index (ABI), which is a simple, inexpensive test. It involves participants lying down for five minutes, during which the blood pressure in their feet is compared to that in their arms. The blood pressures is recorded (above 0.95 is thought to be normal and below 0.95 to indicate narrowing of the arteries to the legs).

The researchers wanted to see if the ABI test could be used in population screening programs to identify people who might benefit from preventive treatments.

The participants were recruited from a community health registry of people living in central Scotland.  28,980 men and women between 50 and 75 years of age were screened. The researchers then excluded anyone who already had diagnosed vascular disease, were already taking medication such as aspirin or warfarin, or were unwilling to take part. This left 3,350 people with an ABI of 0.95 or less who were given aspirin or placebo randomly.

The participants were split into two groups. 1,675 received 100mg of aspirin daily and 1,675 received a placebo. The researchers followed all (except 10) participants for over eight years. Participants were seen at intervals of three months, one year and five years in the clinic and were then contacted annually by phone. They also received a mid-year letter, enquiring generally about any problems, and an end-of-year newsletter.

The researchers monitored fatal or non-fatal heart attacks, stroke or revascularisation (such as angioplasty or bypass grafts). They also looked for all deaths, angina, intermittent claudication (pain in the legs when walking) and warning strokes (transient ischemic attacks). Results were analysed according to the groups which the patients were originally allocated.

 
Basic results

By the end of the trial, 357 participants had had a fatal or non-fatal heart attack, stroke or revascularisation; a rate of 13.5 events per 1,000 person-years (95% confidence interval [CI], 12.2 to 15.0).

There was no statistically significant difference between groups. There were 13.7 events per 1,000 person-years in the aspirin group compared to 13.3 in the placebo group (hazard ratio [HR] 1.03,
95% CI 0.84 to 1.27).

No statistical significance between groups in other outcomes including death from any cause (176 deaths in the aspirin group compared with 186 in the placebo group).

A first major haemorrhage requiring hospital admission occurred in 34 participants in the aspirin group (2.5 per 1,000 person-years) and 20 in the placebo group (1.5 per 1,000 person-years; HR in favour of placebo group, 1.71, 95% CI, 0.99 to 2.97).

 
How did the researchers interpret the results?

The researchers say that in this study “the administration of aspirin compared with placebo did not result in a significant reduction in vascular events.”

 
Conclusion

The trial tried to determine who should be given aspirin to prevent a heart attack or stroke. It used a systematic method to screen people and followed a reasonably large group of patients for up to 10 years in some cases. The finding of “no statistical significance” suggests that any benefits from taking aspirin for this group of people are likely to be small. The risk of bleeding was also small.

    * There is a non-significant trend in the results towards aspirin being harmful. As there is also a suggestion that the study may have been underpowered (planned for too few people), this implies that a larger study may have detected a significant increase in major bleeding in the aspirin group. However, the fact that the reported results were not statistically significant has been picked up by the newspapers.
    * Although there were more bleeds in the aspirin group than the placebo group, they varied in their severity. and not all bleeds had the same implication for patients. For example, some episodes of bleeding from stomach ulcers were easily treated, while other cases of bleeding from haemorrhagic stroke were fatal. There were three fatal haemorrhagic strokes in both groups. Fourteen patients in the aspirin group required admission to control bleeding (reasons not given) compared to five in the placebo group. By combining the bleeding outcomes important information is lost.
    * Considering this trial originally screened about 30,000 people, it is important to keep the small number of patients (9) who died from major haemorrhage in perspective.

Overall, this study has found that aspirin doesn’t appear to be of benefit in preventing cardiovascular disease in this group of patients at least, and suggests it could even increase bleeding. There are other groups of patients, for example, those with high blood pressure, cholesterol and diabetes who may benefit from aspirin. People taking aspirin following a heart attack or stroke should continue to do so, and others should consider being assessed for vascular risk.


References links

Fowkes FGR, Price JF, Stewart MCW, et al. Aspirin for Prevention of Cardiovascular Events in a General Population Screened for a Low Ankle Brachial Index. JAMA 2010; 303: 841-848

Berger JS. Aspirin as Preventive Therapy in Patients With Asymptomatic Vascular Disease. JAMA 2010; 303: 880-882