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Can Prediabetes Put You at Higher Risk for Stroke?

Can prediabetes put you at higher risk for stroke?

About 79 million people in the United States and millions more around the world have prediabetes, which is defined by the American Diabetes Association as an impaired fasting glucose of 100 to 125 mg/dL. A new study indicates people with prediabetes are at higher risk of stroke, but not everyone who fits the definition may be facing this risk.

What is prediabetes and does it matter?

Before 2003, the American Diabetes Association (ADA) defined prediabetes as an impaired fasting glucose (which is raised blood sugar levels after a 12-hour fast, or the fasting plasma glucose test) of 110 to 125 mg/dL. That range was redefined by the ADA in 2003 (by lowering the first number to 100), which in turn also redefined "normal" glucose levels as 70.2 to 100 mg/dL.

In the new meta-analysis, which appears in the current BMJ, a total of 15 studies involving 760,925 participants were analyzed by the authors to determine the relationship between prediabetes and the risk of stroke. Other cardiovascular risk factors such as overweight/obesity, lifestyle, high blood pressure, and smoking were also taken into consideration.

What the researchers found was that individuals who had a fasting glucose level of 110 to 125 mg/dL or who had an impaired glucose tolerance had a 21 percent higher chance of suffering a stroke. But when they applied the new definition of prediabetes to their study, stroke risk disappeared.

Or did it? Does the risk of stroke lie outside the 10 mg/dL difference between 100 mg/dL and 110 mg/dL? The authors emphasized that other unmeasured factors may explain their findings and that the quality of evidence was variable.

They also noted that "the definition of pre-diabetes seems to matter with regard to risk of stroke," and that "the only diagnostic approach for pre-diabetes that is clearly linked to risk seems to be one that includes impairment in glucose tolerance."

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Besides the fasting plasma glucose test, there is another test for prediabetes--the oral glucose tolerance test. This test also involves an overnight fast, and blood glucose is checked after fasting and again two hours after drinking a glucose-rich beverage.

According to this test, normal blood glucose is below 140 mg/dL two hours after the drink. Individuals with a two-hour blood glucose of 140 to 199 mg/dL are determined to have prediabetes, while glucose levels of 200 mg/dL or higher is defined as diabetes.

Another important factor to consider is that the data evaluated in this review did not include studies that involved measurement of hemoglobin A1c, which the ADA recently added as part of its recommended screening process for prediabetes.

Hemoglobin A1c is a blood test that reveals the average amount of glucose in the blood over the past 3 to 4 months. An A1c of 5.6% or lower is normal, while levels between 5.7% and 6.4% are considered prediabetes. Higher percentages are an indication of diabetes.

The authors acknowledged the importance of hemoglobin A1c levels, stating that "ongoing or future prospective cohort studies that include hemoglobin A1c among their baseline variables may provide more information on the association between prediabetes and risk of stroke."

In conclusion they suggested that people with prediabetes be aware they are at a greater risk of stroke and that they should make lifestyle changes to reduce their risk, such as maintaining a healthy weight, nutritious diet, not smoking, controlling high blood pressure, and not smoking. Perhaps the take-home message should be, regardless of where you fall in the prediabetes range, take the necessary steps to reduce your risk of stroke.

American Diabetes Association
Lee M et al. Effect of pre-diabetes on future risk of stroke: meta-analysis. BMJ 2012; 344:e3564

Image: Wikimedia Commons