But, aggressively lowering cholesterol can help reduce that risk, the researchers report.
"Patients who had a stroke or TIA and who have diabetes are at higher risk of having another stroke as compared to patients who have no diabetes or those who have metabolic syndrome," said study researcher Dr Larry B. Goldstein, director of the Duke Stroke Center at Duke University Medical Center in Durham, N.C.
"Moreover, statin treatment was similarly effective in reducing risk in patients with and without type 2 diabetes or metabolic syndrome," he said.
The report was published in the Archives of Neurology.
How the study was done
For the study, the research team analysed data from the Stroke Prevention by Aggressive Reduction of Cholesterol Levels (SPARCL) Trial. This trial was designed to look at whether taking high doses of cholesterol-lowering drugs called statins (in this case, Lipitor) would reduce the risk of having a second stroke or TIA.
The trial did find that lowering cholesterol reduced the likelihood of another cardiovascular event in patients with recent stroke or TIA.
In their analysis, the researchers also looked at the risk of having another stroke, TIA or a heart attack among diabetics and people with metabolic syndrome and whether statin treatment could reduce that risk.
Of the 4,731 people in the trial who had had a stroke or TIA, the researchers identified 794 diabetics and 642 with metabolic syndrome. Metabolic syndrome is a group of conditions, including high blood pressure, high blood sugar and high cholesterol, that increase the odds of developing diabetes and heart disease.
Compared with non-diabetics, people with diabetes were more likely than others to have another stroke, TIA or other cardiovascular event. They were also more likely to need an angioplasty to open blocked arteries.
However, people with metabolic syndrome were not at greater risk of another stroke or TIA or cardiovascular event than those without the syndrome. But they also were at higher risk of needing an angioplasty, the researchers found.
Diabetes and stroke risk
"The main point of the paper is that intensive lipid-lowering in patients with prior stroke or TIA and without known heart disease provides global benefit of risk reduction," said lead researcher Dr Alfred Callahan, from Vanderbilt University Medical Center in Nashville, Tenn.
Dr Ralph Sacco, president of the American Heart Association/American Stroke Association, said the study is largely confirmatory. But it did show that "even among diabetics, statins are still making a difference in terms of reducing risk," he said.
Controlling diabetes is important after a serious cardiovascular event, added Sacco, who is also chairman of the department of neurology at Miller School of Medicine of the University of Miami. "We want people to control their diabetes and also treat their blood pressure and treat their cholesterol," he said.
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