A daily, low dose aspirin tablet is a popular option among people hoping to reduce their risk of cardiovascular disease. In fact, studies support the prophylactic use of aspirin as a simple and cheap way to prevent recurrent heart attacks and stroke. But, does that mean everyone should take a daily low dose aspirin? Findings from the ASPREE trial (Aspirin in Reducing Events in the Elderly) published this week as several studies here, and here and another here, suggest the answer to that question is no.

The problem with aspirin

Aspirin, one of the most commonly used drugs worldwide was originally derived from the herbal medicine, white willow bark. This herbal remedy was used in traditional medicine for thousands of years to relieve pain and inflammation. However, aspirin and white willow are not the same.

White willow bark contains, among other things, a compound called salicin. This compound passes through the stomach intact and absorbed into the blood from the intestines. It is oxidised to salicylic acid in the liver, and it is salicylic acid which is thought to be at least partly responsible for the benefits of white willow and other salicylate-containing herbal medicines.

When scientists discovered that salicylic acid was responsible for the medicinal actions of white willow they attempted to isolate and purify it for use as a drug. Though they were successful, they found the pure chemical had nasty side effects, eroding the stomach wall. Effects that were not seen with use of the herbal remedy. In fact, salicin has little effect on the stomach lining.

With further experimentation scientists were able to chemically alter salicylic acid, producing the derivative acetylsalicylic acid. This compound had greatly reduced gastrointestinal side effects, though not entirely eliminated, and acetylsalicylic acid became the popular drug, aspirin.

Aspirin has many of the benefits of white willow. It has anti-inflammatory properties, and in fact, greater analgesic properties than white willow. However, unlike white willow, aspirin has anti-coagulant properties and was found to increase bleeding time, preventing blood from clotting so easily. Though this effect may be responsible for a reduced risk of heart attacks, it may also increase the risk of unwanted bleeding.

Which brings us back to to the ASPREE clinical trial. This study was designed as a 5 year study and involved over 19,000 thousand healthy people with an average age of 74. Following the success of using low dose aspirin therapy in people with a history of cardiovascular disease in order to prevent a recurrence of heart attack or stroke. Researchers wanted to know if low dose aspirin therapy would prevent disease in healthy elderly people.

They compared the affect of daily low dose aspirin (100mg) with that of a placebo, on healthy elderly people for several outcomes. In the studies published this week their prime areas of interest were, for healthy elderly people, does daily low dose aspirin:

• prevent cardiovascular disease?
• extend disability free lifespan, including risk of dementia or physical disability?
• change risk of death from any cause?

Researchers suggest the findings of the trial show that daily low dose aspirin did not result in significantly lower risk of cardiovascular disease, or prolong disability-free lifespan. However, the aspirin did increase the risk of death (mainly from cancer). The researchers did add that this last result was unexpected and should be interpreted with caution.

In addition, in healthy elderly people, the ASPREE clinical trial showed a daily low dose aspirin was found to significantly increase the risk of major haemorrhage compared to placebo. What’s more, from these results we can conclude that for healthy elderly people the risks of daily aspirin use may in fact outweigh the benefits.

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