The study found that in nearly 1,300 adults with no symptoms of heart disease the drug, which can cause stomach bleeds, had no benefit.
The findings contradict many guidelines, which advocate people with diabetes use aspirin to counter the underlying high risk of heart attack and stroke.
But there are key high-risk groups who still need the drug, experts said.
Patients with diabetes are two to five times more likely to suffer from heart disease than the general population and heart disease is a major cause of death in patients with type 1 and 2 diabetes.
To reach the conclusion, professor Jill Belch and colleagues from Scotland investigated whether aspirin and antioxidants given together or separately can reduce heart attacks and death in patients with diabetes and arterial disease. 1276 patients with diabetes and evidence of artery disease over 40 years of age were randomised to receive either aspirin or placebo, an antioxidant or placebo, aspirin and antioxidant or double placebo, and followed over eight years.
Overall, the researchers found no benefit from either aspirin or antioxidant treatment in the prevention of heart attacks or death. Patients in the aspirin groups had 116 primary events compared with 117 in the placebo group. No significant difference in events was seen between the antioxidant group and the placebo group.
The study has been published in the British Medical Journal.