Dr Gerald Fowkes and colleagues from the University of Edinburgh used ankle brachial index (ABI) as a marker of vascular event risk. They studied the effectiveness of aspirin at preventing vascular events in a group of 3,350 healthy people with a low ABI.

Half took aspirin 100mg once daily, while the other half were given a placebo.

After more than eight years, the researchers found there was no difference in the vascular event rate between the two groups, suggesting aspirin offers no protection against vascular events in those at high risk.

There were 13.7 events per 1,000 person-years in the aspirin group, compared with 13.3 events in the placebo group.

The researchers said a lack of statistical power to detect small effects of aspirin may have affected the study's outcome.

The trial was designed to be able to detect a 25 per cent risk reduction in vascular events among participants. But the researchers suggest that this estimate may have been too high.

The study findings suggested a possible risk reduction of around 16 per cent, the researchers said.

But a risk reduction of this size would be outweighed by the increased risk of major haemorrhage and GI ulcer, as well as more instances of fatal intracranial adverse events in the aspirin group, the researchers said.

Writing in an accompanying editorial, Dr Jeffrey Berger of the New York University School of Medicine said the trial may have implications for screening using ABI.

'Because aspirin did not reduce rates of cardiovascular events in the participants found to have low ABI, these data do not support recommendations for ABI screening in an effort to ultimately reduce cardiovascular disease event rates in patients at risk for peripheral artery disease,' he wrote.

• JAMA Online 2010