Types 1 and 2 Diabetes May Increase Risk for Most Stroke Subtypes in Women

July 17, 2007 — Types 1 and 2 diabetes mellitus raise the risk for most stroke subtypes in women, according to the results of The Nurses' Health Study published in the July issue of Diabetes Care.
"In many but not all epidemiological studies, type 2 diabetes has been an important risk factor for ischemic stroke; however, relative risks (RRs) have varied widely, from 1.3 to 4.9," write Mohsen Janghorbani, PhD, from Isfahan University of Medical Sciences in Iran, and colleagues. "In contrast, the association with hemorrhagic stroke remains controversial; reported associations have been positive, null, or even inverse. Further, only a few small studies have examined the risk of stroke in patients with type 1 diabetes, and this relationship remains unsettled."
The investigators followed up 116,316 women aged 30 to 55 years in 1976 through 2002 for incidence of stroke. These women were asked about their history and treatment of diabetes and other potential risk factors for stroke at baseline and at biennial follow-up.
During 2.87 million person-years of follow-up, there were 3463 incident strokes. Multivariate analyses showed that the incidence of total stroke was 4-fold higher in women with type 1 diabetes mellitus (RR, 4.7; 95% confidence interval [CI], 3.3 - 6.6) and 2-fold higher in women with type 2 diabetes mellitus (RR, 1.8; 95% CI, 1.7 - 2.0) than in women without diabetes. For ischemic stroke, RR was 6.3 (95% CI, 4.0 - 9.8) in type 1 and 2.3 (95% CI, 2.0 - 2.6) in type 2 diabetes mellitus.
For large-artery infarction and lacunar stroke, risks were similar. Although type 1 diabetes mellitus was significantly associated with the risk for hemorrhagic stroke (RR, 3.8; 95% CI, 1.2 - 11.8), type 2 diabetes mellitus was not (RR, 1.0; 95% CI, 0.7 - 1.4).
"Both type 1 and type 2 diabetes are associated with substantially increased risks of total and most subtypes of stroke," the authors write. "Type 1 diabetes is associated with excess risk of hemorrhagic stroke. The risk of stroke is also associated with duration of type 2 diabetes."
Study limitations include small number of cases of subarachnoid or intraparenchymal hemorrhage, diabetes being determined by self-report and confirmed through a validated diagnostic questionnaire, possible misclassifications, and lack of generalizability to racial/ethnic groups other than white or to men.
"With the worldwide increasing prevalence of diabetes, the population-attributable risk of stroke will probably increase," the authors conclude. "Our results also emphasize the importance of controlling all known stroke risk factors, especially hypertension, in patients with diabetes."
The National Institutes of Health supported this study. The costs of publication of this article were defrayed in part by the payment of page charges, mandating that this article must therefore be hereby marked "advertisement" solely to indicate this fact.
Diabetes Care. 2007;30:1730-1735.