Nonfasting Serum Glucose and Insulin Concentrations and the Risk of Stroke

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Abstract
Background and Purpose —Type 2 diabetes is an established risk factor for stroke, but the relations between asymptomatic hyperglycemia, hyperinsulinemia, and stroke incidence remain uncertain. We have examined the relationship between established diabetes, nonfasting serum glucose and serum insulin concentrations, and subsequent risk of stroke. Methods —We performed a prospective study of 7735 men aged 40 to 59 years drawn from general practices in 24 British towns. Men with missing serum glucose values (n=50) and men on insulin injection (n=36) were excluded, leaving 7649 men available for analysis. Baseline nonfasting serum was analyzed for insulin with a specific enzyme-linked immunosorbent assay method in 18 of the 24 towns (n=5663 men). Results —During the mean follow-up period of 16.8 years, there were 347 stroke cases (fatal and nonfatal) in the 7649 men. Men who developed diabetes during follow-up (n=320) and men with established type 2 diabetes at screening (n=98) both showed significantly increased risk of stroke, even after adjustment for cardiovascular risk factors, including blood pressure (adjusted relative risk [RR], 2.27; 95% CI, 1.23 to 4.20; RR, 2.07; 95% CI, 1.44 to 2.98, respectively). In men with no diagnosed diabetes at screening (n=7551), risk of stroke was increased significantly only in the top 2.5% of the nonfasting glucose distribution (≥8.2 mmol/L), and this persisted even after adjustment for cardiovascular risk factors, including hypertension (RR, 1.86; 95% CI, 1.11 to 3.13). Exclusion of the 320 men who developed diabetes during follow-up attenuated this risk so that it was no longer significant (RR, 1.56; 95% CI, 0.83 to 2.91). In the 5567 men with insulin measurements and no diagnosis of diabetes at screening, a J-shaped relationship was seen between nonfasting insulin and risk of stroke. Risk was significantly raised in the first quintile and in the fourth quintile and above compared with the second quintile, with all findings of marginal significance. Part of the increased risk at higher levels of insulin was due to men who developed diabetes in the follow-up period. Conclusions —This study confirms the importance of established type 2 diabetes as an independent risk factor for stroke. The increased risk of stroke seen in hyperglycemic subjects and those with elevated serum insulin levels at screening reflected to some extent the high proportion of men who subsequently developed diabetes.