A Johns Hopkins study suggests that people with type I
and type II diabetes would be well advised to monitor their
blood sugar levels more than the usual twice daily to make
sure that levels are not elevated over 150 milligrams per
deciliter for sustained periods.
A research team at Johns Hopkins has added new and
detailed evidence of the link between elevated blood sugar
levels in people with diabetes and increased risk of
developing life-threatening forms of cardiovascular disease
— including coronary heart disease, stroke and
peripheral artery disease. Their findings, part of a broad
retrospective meta-analysis 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," says the study's senior author, endocrinologist
Sherita Golden, assistant professor of
medicine and
epidemiology at the
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 1 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, 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," Golden says. "It will be
challenging for patients to achieve tight glycemic control
[of 7 percent 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 Johns 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,
Spyridon Marinopoulous, Gail Berkenbilt, Tejal Rami,
Frederick Brancati and Neil Powe.