In a surprising outcome, investigators at Wake Forest University Baptist Medical Center found that diabetic black men have dramatically lower amounts of atherosclerosis, or hardening of the arteries, than diabetic white men.
Barry I. Freedman, M.D., and colleagues report in the December issue (Volume 48, No. 12) of Diabetologia that African-American men had significantly lower levels of calcified atherosclerotic plaque in the coronary (heart) arteries and the carotid arteries in the neck that supply blood to the brain.
"This striking result was observed despite black subjects having higher levels of conventional risk factors for heart disease," said Freedman. "These risk factors would normally be expected to promote coronary artery disease in the black participants."
This result was also observed in the face of increased thickness of carotid artery walls in black diabetic subjects. Increased wall thickness is widely accepted – including by the U.S. Food and Drug Administration – as a marker for atherosclerosis and a predictor of coronary heart disease, so the result was surprising.
Freedman said that in women, "ethnic differences in calcified carotid artery plaque, but not coronary artery plaque, were observed."
The amount of plaque was measured using high-speed computed tomography (CT) scans.
The results came from the Diabetes Heart Study, made up of North Carolina families in which at least two siblings have type 2 or non-insulin-dependent diabetes. The investigators – all from Wake Forest – recruited 1,000 white participants from 369 families and 180 blacks from 74 families for this study.
Freedman said the black subjects had higher blood pressures, higher levels of low-density lipoprotein (LDL ) cholesterol (the bad cholesterol), higher overall cholesterol, elevated blood sugars and a host of other measures that are considered risk factors for atherosclerosis.
Freedman, the John H. Felts III, M.D., Professor of Internal Medicine and head of the Section on Nephrology, said the study was the first to compare blacks and whites who had type 2 diabetes for differences in atherosclerosis.
"Hardening of the arteries appears to be a different disease in blacks and whites. We have demonstrated this in diabetic subjects; other groups have shown it in people with hypertension," said Freedman. "We should be studying what causes these biologic differences. Perhaps inherited or genetic influences may contribute to these differences."
He said that these differences are in line with the results from two large clinical studies. These studies revealed that the risk of heart attack in blacks was half that in whites, when access to care was equal.
"No one would disagree that in the general population, blacks have higher death rates from heart attack and stroke. This may relate to the fact that blacks don't always have equal access to quality healthcare," Freedman said. "But once you have equal care, there are differences in outcome that suggest that biologic differences exist in atherosclerosis."
Freedman said 14.9 percent of all blacks have diabetes – some undiagnosed – and an additional 6.3 percent have impaired glucose tolerance, which means that the body is processing carbohydrates much more slowly. "On average, an African-American individual is twice as likely to have diabetes as his or her white peer. The prevalence of diabetes among African-Americans aged 40 to 74 doubled from 8.9 percent in 1976-1989 to 18.2 percent in 1988-1994."
Other investigators in the study include Fang-Chi Hsu, Ph.D., Carl D. Langefeld, Ph.D., Stephen S. Rich, Ph.D., Jianzhao Xu, B.S., and Lynne Wagenknecht, Dr. P.H., from the Department of Public Health Sciences, David M. Herrington, M.D., from Cardiology, Donald W. Bowden, Ph.D., from Biochemistry, and J. Jeffrey Carr, M.D., from Diagnostic Radiology.