Rising blood sugar points to developing stroke risk

By Eleanor McDermid

People with prediabetes have a somewhat increased risk for stroke, say the authors of a meta-analysis.

Although the effect was "relatively modest" and could be at least partly caused by residual confounding, the detection of prediabetes should trigger a review of patients' vascular risk profiles, say Bruce Ovbiagele (University of California, San Diego, USA) and colleagues.

The presence of prediabetes raised stroke risk about 20% overall, but the effect was smaller in the nine studies the team judged to have adequate adjustment for confounders than in the six with inadequate adjustment.

The effect of prediabetes was also heavily dependent on the definition used. Eight of the 15 studies (760,925 patients in total) defined prediabetes according to the American Diabetes Association's current definition of fasting glucose 100-125 mg/dL (5.6-6.9 mmol/L); prediabetes by this definition conferred a nonsignificant 8% increase in stroke risk, relative to normal glucose levels.

With a more stringent definition of fasting glucose 110-125 mg/dL (6.1-6.9 mmol/L), as used in five studies, prediabetes raised stroke risk a significant 21%.

The effect was strongest in eight studies that defined prediabetes as having impaired glucose tolerance, with or without raised fasting glucose, at a 26% increase in stroke risk.

This "reinforces the notion that two hour postprandial glucose challenge is probably a stronger predictor of macrovascular complications than is fasting glucose," the researchers write in the BMJ.

In studies reporting the effects of impaired glucose tolerance, the effect on stroke risk was far stronger in four with inadequate adjustment for confounders, at a 60% increase, than in four with adequate adjustment, at a nonsignificant 11% increase.

The team notes that the American Diabetes Association now includes hemoglobin A1c between 5.7% and 6.4% in its diagnostic criteria for prediabetes, but this information was not available in the studies in the meta-analysis, so its effect on stroke risk remains unknown.

Nevertheless, the researchers conclude that people with prediabetes should be warned of their increased stroke risk and that the discovery of prediabetes should prompt a general review of a patient's cardiovascular risk factor profile.

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