Blood sugar and a protein combine to increase bleeds
One reason why people with diabetes can suffer more damage during strokes has been discovered by US scientists.
The study on rats, published in Nature Medicine, found a protein which increased bleeding when blood sugar levels are high.
Elevated sugar levels have been linked to at least one in ten strokes.
Diabetes UK said the big test was whether the research would lead to clinical benefits for people with high sugar levels.
It is thought that 150,000 people in the UK have a stroke each year, more than a third die as a result.
There are two main types, 80% are caused by blood clots in the brain (ischaemic stroke) and 20% when blood vessels bleed into the brain (haemorrhagic stroke).
More than half of people with haemorrhagic strokes have high levels of sugar in the blood.
The haemorrhages also seem to be more severe, forming over a larger area of the brain, causing more damage and increasing the risk of death.
Linking sugar and stroke
Scientists at the Joslin Diabetes Centre injected blood into the brains of rats with and without diabetes.
The bleeding was ten times greater in those with diabetes than in healthy rats.
The group then studied the impact of a protein, plasma kallikrein, which had already been linked to sight problems in diabetics.
The researchers found that a combination of high blood sugar and plasma kallikrein resulted in increased bleeding.
They believe plasma kallikrein slows clotting when there is lots of sugar in the blood, although the exact mechanism remains unclear.
Dr Edward Feener, who led the study, said: "Given the prevalence of strokes and the damage they inflict, these findings are exciting because they suggest the possibility that rapid control of blood sugar levels may provide an opportunity to reduce intracerebral haemorrhage, which is a clinical situation that has very limited treatment options.
"This work could have broad implications since about half of patients with acute haemorrhagic stroke have hyperglycemia, whether or not that have pre-existing diabetes."
Dr Sharlin Ahmed, research liaison officer at The Stroke Association, said: "Diabetes is known to increase a person's risk of stroke, and research has shown that strokes caused by a bleed in the brain are more severe in people with diabetes as a result of poorly controlled blood sugar levels.
"Controlling glucose levels is vital if you have diabetes. This research not only provides further evidence that glucose control can reduce your risk of stroke, but it also suggests that it could reduce the severity of a stroke caused by a bleed in the brain.
"However, it is very early days and much more research needs to be carried out before human trials are undertaken."
Dr Iain Frame, director of research at Diabetes UK, said: "This early research has made an interesting discovery into how high blood glucose levels interact with certain chemicals in the blood, and with the damage caused by stroke.
"As the authors admit, however, there are limitations in the animal model they used so their results do not reflect what happens to the human brain when it haemorrhages.
"Much more research is needed to test how we might be able to use this knowledge to limit this stroke damage and that will prove to be the big test as to whether this study will lead to any benefits for people with high glucose levels who have a stroke."