An article in the current issue of JAMA reports on the efficacy of low-dose aspirin for the primary prevention of atherosclerotic events in patients with type 2 diabetes.

This was a multicenter, prospective, randomized, open-label, blinded, end-point trial conducted from December 2002 through April 2008 at 163 institutions throughout Japan, involving 2539 patients with type 2 diabetes without a history of atherosclerotic disease and had a median follow-up of 4.37 years.

Patients took either 81 or 100 mg of aspirin per day, or nothing.

Although there were less atherosclerotic events in the aspirin group (68 vs 86), given the size of the groups, the results did not reveal any significant differences (p=0.16).

So, as far as this study is concerned, low-dose aspirin did nothing for those with type-2 diabetes.

Why does low-dose aspirin has a reputation for lowering the risk of untoward cardiac events? Daily low-dose aspirin is known as anti-platelet therapy, due to its ability to prevent platelets aggregating and causing the blood to clot. It is via this mechanism that it reduces the likelihood of cardiovascular events, and it is currently endorsed by the American Heart Association specifically for this purpose:

The American Heart Association recommends aspirin use for patients who’ve had a myocardial infarction (heart attack), unstable angina, ischemic stroke (caused by blood clot) or transient ischemic attacks (TIAs or “little strokes”), if not contraindicated. This recommendation is based on sound evidence from clinical trials showing that aspirin helps prevent the recurrence of such events as heart attack, hospitalization for recurrent angina, second strokes, etc. (secondary prevention). Studies show aspirin also helps prevent these events from occurring in people at high risk (primary prevention).

Given the apparent weight of evidence supporting the daily use of aspirin as a preventative therapy, it’s quite strange that there appear to be few effects in type-2 diabetes sufferers. The Japanese study could be considered to be underpowered due to the very small number of cardiovascular events occurring in either group; another weakness was that it was not double-blinded nor randomized.

The authors of the study admit that the results do not suggest that low-dose aspirin is ineffective, but rather that their study design did not produce conclusive results, and possibly that overriding factors in diabetes sufferers contribute to cardiovascular problems far more than the protective effect conferred by aspirin therapy.

So there you go.