In addition to a 30% greater chance of an ischemic stroke, the researchers also found that people who had type 2 diabetes in their 40s or 50s were twice as likely to have narrower blood vessels in their brain in their 60s and beyond.
“Our findings highlight the need for controlling midlife type 2 diabetes mellitus to help prevent [ischemic stroke and narrowing of the blood vessels in the brain],” said study author Rongrong Yang. Yang is a Ph.D. candidate at Tianjin Medical University in China.
An ischemic stroke, which is the more common type of stroke, is caused by a blockage in a blood vessel in the brain. This damages the area of the brain that’s no longer receiving enough blood. The less common type of stroke is known as a hemorrhagic stroke. That type of stroke occurs when a blood vessel bursts, causing blood to leak into the brain and cause swelling and tissue damage, the National Stroke Association says.
Type 2 diabetes has long been associated with the risk of stroke, but it’s been hard to know if an increased risk of stroke comes from the diabetes or from other genetic and environmental factors, according to background information in the study.
To better tease out if diabetes itself was a likely culprit, the researchers reviewed data from the Swedish Twin Registry. More than 33,000 twin individuals met the criteria for the study.
The study participants were all born before 1958. None had evidence of narrowed brain blood vessels or stroke before age 60.
Just under 4% of the group had diabetes in midlife. More than 9% had late-life (after 60) strokes or narrowed blood vessels in their brain, the study authors said.
After adjusting the data to account for other stroke risk factors, such as smoking and obesity, the researchers noted the increased risk of ischemic stroke, but didn’t find an increased risk of hemorrhagic stroke.
So why might diabetes lead to more ischemic strokes?
“The mechanisms underlying the association of type 2 diabetes mellitus with stroke are complex and not completely understood,” Yang said. But, people with type 2 diabetes have abnormal cholesterol levels and that might contribute to the narrowed blood vessels in the brain.
Dr. Joel Zonszein, director of the clinical diabetes center at Montefiore Medical Center in New York City, said the Swedish population has significantly less type 2 diabetes than would be found in the United States.
Zonszein was not, however, surprised to see a higher risk of stroke and narrowed blood vessels in people with diabetes.
“We need to be much more alert to getting the proper diagnosis of diabetes and controlling risk factors. Focus on the things we can change to try to improve risk factors,” Zonszein said.
“Smoking cessation is important, and we have to treat high blood pressure. High blood pressure puts people at high risk of stroke. People with diabetes should be on a statin to control cholesterol levels, and they should be on the proper medications to control their diabetes,” he added.
Study author Yang agreed that controlling risk factors is key.
“Diabetic patients need to maintain a healthy lifestyle, such as doing regular exercise, eating a healthy diet, keeping a healthy weight, no smoking, as well as [blood sugar] control, in order to reduce the risk of [stroke] in late life,” Yang said.
The findings were published June 5 in Diabetologia.