Their findings, part of a broad retrospective meta-analysis to be published in the Annals of Internal Medicine online Sept. 21, suggest monitoring long-term blood sugar control by level of glycated hemoglobin (also called glycosylated hemoglobin) and adding this measurement to regular monitoring of cholesterol levels and blood pressure.
"The relationship between blood sugar levels - or glycemic control - in people with diabetes and whether this increases their risk of developing heart disease has remained unclear until now, despite many different studies about specific types of cardiovascular problems," said the study's senior author, endocrinologist Sherita Golden, M.D., M.H.S., assistant professor of medicine and epidemiology, at The Johns Hopkins University School of Medicine and Bloomberg School of Public Health.
"People living with diabetes are twice as likely to die from cardiovascular disease compared to those without diabetes. As a result, many people living with diabetes monitor their health for well-known risk factors for heart disease, such as obesity, cholesterol levels and blood pressure - but, the big unknown has been the role of blood sugar levels in managing their risk of developing cardiovascular disease."
After pooling and re-analyzing the data from 13 previously published studies - involving nearly 10,000 people from North America and Europe with type I or type II diabetes - the researchers concluded that for every 1 percent rise in glycated hemoglobin levels, there was an 18 percent increase in the risk of developing large-vessel cardiovascular disease among people with type II diabetes.
For people with juvenile onset or type I diabetes, the researchers found a similar increased risk of 15 percent for every one percent rise in levels of glycated hemoglobin; however, as there were fewer studies involving people with type I diabetes, this risk estimate is not as reliable as the estimate for type II.
A landmark British study in 1998, the United Kingdom Prospective Diabetes Study (UKPDS), first nailed down the direct link between control of blood sugar levels in people with type II diabetes and risk of developing small-vessel disease, where excessive levels of blood sugar can have serious long-term consequences, including blindness, kidney damage and peripheral nerve disease. However, this study was largely considered inconclusive by the medical community because it lacked statistically significant results, and despite results that showed a 16 percent decrease in large-vessel cardiovascular disease in people whose blood sugar levels were aggressively treated. Hence, the U.K. study did not fully clarify the need for or frequency of monitoring for prevention of large-vessel disease.
The monitoring of glycated hemoglobin is a longer-term measure of blood sugar control, reflecting a three-month average of blood sugar levels. This contrasts with the more commonly known measurement of milligrams per deciliter, which reflects daily blood sugar levels, and is used by people with diabetes, who often carry finger-prick devices to check their blood glucose levels throughout the day. The current desired range for daily control of blood sugar levels is 80 to 120 mg/dL, prior to meals.
"Our research suggests that management of blood sugar levels is still a key part of cardiovascular disease prevention in diabetes," said Golden. "It will be challenging for patients to achieve tight glycemic control (of 7% HbA1c, or less, approximately 150 mg/dL on a daily basis). However, we now have more information to counsel and motivate patients to better self care. In people with diabetes, particularly type II, we must consider monitoring and aggressively treating all three risk factors for heart disease: cholesterol, blood pressure and blood sugar levels. People with type II diabetes want to avoid any prolonged periods when their blood sugar levels exceed 150 mg/dL."
During the 18-month study, the Hopkins team carefully evaluated 694 published articles that looked at glycated hemoglobin as a measure of glycemic control and cardiovascular disease. Of these, 69 articles were selected for thorough review of methodology and data to determine which data sets should and could be pooled for group analysis. In the end, 13 studies were selected: Three looked at type I diabetes, and 10 involved type II diabetes. Among the major studies pooled into the larger analysis were results from the 1998 UKPDS and the 1999 Wisconsin Epidemiology Study of Diabetic Retinopathy, another long-term study of patients.
According to the latest statistics from the International Diabetes Federation, in 2001, more than 13 million Americans live with type II diabetes. Type II diabetes is more common in African, Hispanic and Native Americans than in Caucasians.
This study was funded by the national Agency for Healthcare Research and Quality and with grants from the National Institutes of Health. Further assistance was provided from the Robert Wood Johnson Foundation's Harold Amos Minority Medical Faculty Development Program.
Other investigators in this research, conducted solely at Johns Hopkins Evidence-Based Practice Center and Bloomberg School of Public Health, were lead author Elizabeth Selvin, M.P.H., Spyridon Marinopoulous, M.D., M.B.A.; Gail Berkenbilt, M.D., Ph.D.; Tejal Rami, M.P.H.; Frederick Brancati, M.D., M.H.S.; and Neil Powe, M.D., M.P.H., M.B.A.
Note to Editors:
A video news release accompanies this study, courtesy of the American College of Physicians, publishers of the Annals of Internal Medicine.
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