Duration of Diabetes Raises Stroke Risk

By Todd Neale, Senior Staff Writer, MedPage Today

Published: March 01, 2012

Reviewed by Dori F. Zaleznik, MD; Associate Clinical Professor of Medicine, Harvard Medical School, Boston and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner

The risk of ischemic stroke increased by 3% for each additional year a patient had diabetes, researchers found.

Compared with nondiabetics in the longitudinal study, those who had the disease for at least 10 years had a threefold higher stroke risk (HR 3.2, 95% CI 2.4 to 4.5), Mitchell Elkind, MD, of Columbia University in New York City, and colleagues reported online in Stroke: Journal of the American Heart Association.

Although stroke rates have been dropping among diabetics, more people are developing the disease -- and at younger ages -- because of the obesity epidemic. That means that the stroke burden is growing heavier, particularly as the population ages and people live longer.

"It is thus important to better understand the dynamics between diabetes, time, and stroke, and to emphasize the importance of interventions to prevent early diabetes," the authors wrote. "Minimizing the number of years a patient has diabetes would help combat the increase in stroke risk with each year of the disease."

Elkind and colleagues examined data from 3,298 individuals participating in the Northern Manhattan Study who had never been diagnosed with a stroke. The average age was 69. Half of the participants were Hispanic, 21% were white, and 24% were black.

About one-fifth (22%) had diabetes at baseline and another 10% reported new-onset diabetes during an average follow-up of nine years.

There were 244 ischemic strokes recorded during the study.

After adjustment for demographics and cardiovascular risk factors, ischemic stroke was predicted by the presence of baseline diabetes (HR 2.5, 95% CI 1.9 to 3.3) and diabetes as a time-dependent variable (HR 2.4, 95% CI 1.8 to 3.2), which takes into account the development of diabetes during follow-up.

The researchers had hypothesized that incorporating incident diabetes would change the magnitude of the association, but it did not, possibly because these older individuals already had a high cardiovascular risk burden at baseline that did not change much with the development of diabetes.

Other possible reasons incident diabetes did not improve risk prediction included greater compliance with therapy among those newly diagnosed, a shorter duration of diabetes among the incident cases, which might not be long enough to translate into a higher stroke risk, and the potential for missing cases during follow-up because of the use of self-report.

Compared with nondiabetics, the risk of ischemic stroke was similar for those who had diabetes for up to five years (HR 1.7) and those who had the disease for five to 10 years (HR 1.8). The risk was greater for those who had diabetes for a decade or more (HR 3.2).

The growing stroke risk that accompanies a longer duration of diabetes could be mediated through several mechanisms, according to the researchers:

Greater carotid plaque thickness
Accelerated microvascular and macrovascular complications from long-term hypertension
Greater risk of microalbuminuria, which has been shown to be a risk factor for stroke in patients with diabetes
Endothelial dysfunction
Abnormalities in fibrinogen and clotting mechanisms

The finding "warrants steps to institute long-standing and sustainable lifestyle changes for primary prevention and appropriate long-term management after diagnosis," the authors wrote.

They acknowledged some limitations of the study, including the lack of information on fasting blood glucose and glycated hemoglobin during follow-up and possible confounding of the association between diabetes duration and stroke risk by age.

The Northern Manhattan Study is funded by a grant from the National Institute of Neurological Disorders and Stroke.

The authors reported that they had no conflicts of interest.

From the American Heart Association: