However, the researchers found no such correlation between insulin resistance in African Americans, even though middle-age African Americans are four times more likely than whites to suffer from strokes.
"For whites it will soon be recognized as one of the big risk factors for the development of atherosclerosis," said Dr. George Howard of the Bowman Gray School of Medicine of Wake Forest University. "It's not now."
Howard presented the research during an international medical conference in Winston-Salem.
Howard and others studied insulin resistance as part of a broad-based Insulin Resistance Atherosclerosis Study. Preliminary findings in the study suggest that 90 percent of diabetics and 10 to 20 percent of non-diabetics are insulin resistant.
Insulin is secreted by the pancreas and processes glucose in the blood that is produced when the body metabolizes carbohydrates. Insulin secreted by people who are insulin-resistant is not very efficient at processing glucose.
Atherosclerosis is a narrowing of the artery due to build up of fatty substances, calcium and blood clotting materials on the interior artery walls. The carotid arteries serving the brain are particularly susceptible. Stroke can result when the carotid artery walls narrow to the point that the brain does not get sufficient blood.
Howard will present the researchers' findings on August 16 at International Neurosonology '97. The conference, which ends today, has drawn doctors from around the world to review the latest research on the medical uses of ultrasound. It is being sponsored by the World Federation of Neurology and the Bowman Gray School of Medicine of Wake Forest University.
The researchers used ultrasound to measure the extent of atherosclerosis in a test population of 1,625 people. After controlling for such factors as diet, cholesterol levels, age and other factors, the research showed that a moderate difference in insulin resistance had as large an impact on atherosclerosis in whites and Hispanics as other major risk factors, such as hypertension. However, no such association was present in African Americans.
Howard said there is no clear reason why insulin resistance is a risk factor in whites and Hispanics, but not African Americans, especially given African Americans' greater propensity for strokes. "That's a great mystery," he said. "Science sometimes raises more questions than it can answer."
Because of the high correlation the study found between diabetes and insulin resistance, the research is especially significant to the estimated 16 million Americans who have diabetes.
Howard said he suspects that one reason many people who are insulin resistant have diabetes is the tremendous amount of extra insulin that insulin-resistant people must produce to process the glucose in their blood. After a while, he said, their pancreas simply "wears out" and they become diabetic.
Currently there is no easy way to test for insulin resistance, Howard said. However, a simple lab test is under development that should be available "fairly soon," he said. Once detected, doctors could prescribe drugs already on the market that treat insulin resistance.
The study marks an expansion in the use of ultrasound to detect disease before symptoms appear. "Typically ultrasound is used on sick people," Howard said. "But it's also a good device to measure disease in the general population."
For further information, call Mark Wright (email: mwright@bgsm.edu) or Bob Conn (email: rconn@bgsm.edu) at 910-716-4587. Once International Neurosonology '97 has begun on August 13, call the conference press room at 910-724-6923.