"It is well known that obesity is a contributor to insulin resistance," said senior researcher Jorge Calles-Escandon, M.D. "Our research suggests that race may also be an important factor. Almost half of lean, black women had insulin resistance - double the rate in Hispanic or Caucasian women."
The results were reported today at ENDO 2006, the annual meeting of the Endocrine Society in Boston.
The goal of the study was to see how obesity relates to insulin resistance in three ethnic groups: black, Caucasian and Hispanic. Insulin resistance is when the body does not effectively use the hormone insulin to process glucose, forcing the pancreas to produce more insulin. Researchers analyzed data from the Insulin Resistance Atherosclerosis Study (IRAS), designed to assess relationships between insulin resistance and cardiovascular disease in a large multi-ethnic population.
For the study, the researchers divided data from female IRAS participants into different groups based on body mass index (BMI), a measure of body fat based on height and weight. A BMI of less than 25 is considered "normal." For example, a woman who weighs 148 and is 5 feet, 6 inches, has a BMI of 25.
The analysis revealed that 47 percent of black women of normal weight had insulin resistance, compared to less than 20 percent of the Hispanic or Caucasian women.
"Our research suggests that race, in addition to obesity, is an important contributor to the development of insulin resistance and possibly to type 2 diabetes," said Jennifer Wolfgang, D.O., an endocrinology fellow, who presented the results.
Both insulin resistance and the likelihood of developing type 2 diabetes increase as obesity increases, but it was not previously known that race alone may influence insulin resistance. Type 2 diabetes, the most common form, is when the body does not produce enough insulin or does not respond to even very high levels of insulin, which causes glucose to build up in the blood.
It is not know how many people with insulin resistance develop diabetes and cardiovascular disease, but it is assumed that treating insulin resistance with weight loss and exercise will help prevent those diseases.
Calles-Escandon, an associate professor of endocrinology, said that the results suggest that the definition of "obesity" may need to be redefined in black women. "If the results hold true, black women may need to be evaluated and treated for insulin resistance and cardiovascular disease even at weight not considered obese by current standards," he said.
He said additional research is needed to explore how obesity relates to insulin resistance in men, as well as whether the women with insulin resistance have a higher percentage of body fat, or body fat that is distributed differently, from the Caucasian or Hispanic women.
Other potential areas of research include determining if certain genes in blacks lead to insulin resistance, and whether the insulin resistance is accompanied by other changes that may promote diabetes, cardiovascular disease and diabetes, including reduced elasticity of vessels or deposits of calcium in the vessels leading to the heart.
IRAS involved 1,625 people from San Antonio, Texas, San Luis Valley, Colo., and Oakland and Los Angeles, Calif.
Funders of the research included the National Institutes of Health.
Other researchers were Ralph B. D'Agostino Jr., Ph.D., and Lynne E. Wagenknecht, Ph.D., both from Wake Forest.
Wake Forest University Baptist Medical Center is an academic health system comprised of North Carolina Baptist Hospital and Wake Forest University Health Sciences, which operates the university's School of Medicine. U.S. News & World Report ranks Wake Forest University School of Medicine 18th in family medicine, 20th in geriatrics, 25th in primary care and 41st in research among the nation's medical schools. It ranks 32nd in research funding by the National Institutes of Health. Almost 150 members of the medical school faculty are listed in Best Doctors in America.