A drug given to help people with diabetes may also slow thickening of the artery walls that can lead to heart disease, research suggests.
Thickened arteries is a sign of heart disease
Pioglitazone helps improve the body's sensitivity to the hormone insulin, often lacking in type 2 diabetes.
Tests on patients given pioglitazone showed their arteries were less thick than those given another diabetes drug.
The University of Chicago study was published online by the Journal of the American Medical Association.
People with diabetes, who cannot produce enough insulin or do not respond to the hormone in the normal way, have a higher risk of heart attack.
Controlling these patients' blood pressure and cholesterol levels has been shown to cut some - but by no means all - of this extra risk.
The Chicago team gave either pioglitazone, or a different diabetes drug, glimepiride, to 462 patients with type 2 diabetes.
Regular ultrasound measurements were made of the thickness of the middle layers of the carotid arteries, which are found in the neck and carry blood to the brain.
After 72 week, the thickness of the arteries increased by an average of 0.012 millimetres in the glimepiride group.
But among the patients given pioglitazone, average thickness actually fell by 0.001 millimetres.
Pioglitazone patients also recorded lower levels of sugar in their blood, and higher levels of beneficial HDL cholesterol.
The researchers said the beneficial effect on artery thickness might be down to this good blood chemistry - or some, as yet unknown, direct impact on the artery wall.
Ellen Mason, cardiac nurse at the British Heart Foundation, said: "Diabetes is on the increase and contributes heavily to the risk of developing coronary heart disease.
"For those with diabetes, controlling the glucose levels in the blood is vital - this helps to protect the blood vessels from harm.
"Whether the slowed progression of artery wall thickening would indeed translate into fewer heart attacks amongst people with diabetes remains to be seen - further studies are needed."
Zoe Harrison, from the charity Diabetes UK said: "The use of this treatment is currently restricted and as this trial is relatively small, more research will be needed before it is recommended for more widespread use.
"We welcome more research in this area but emphasise the importance of effective diabetes management in order to reduce heart disease risk."
Pioglitazone is one of a class of drugs known as thiazolidinediones.