Diabetes and heart disease are reaching epidemic proportions in people of African descent. To reverse this trend and improve longevity and quality of life, clarity on the causes of cardiometabolic disease in people of African descent and improved screening is necessary. Diabetes and heart disease result from the combined effects of insulin resistance and hyperinsulinemia. The earliest etiological and epidemiological studies were done in populations of white European descent such as Framingham, the Nurse’s Health Study and the Physician’s Health Study. This initial work demonstrated that insulin resistance and the associated hypertriglyceridemia were the major and earliest causes of cardiometabolic disease. This research subsequently informed the development of screening tests for diabetes and heart disease. Hence, the majority of screening tests for diabetes and heart disease focus on triglyceride (TG) levels and insulin resistance. These TG-based screening tests depend on the principle that elevated TG levels are an excellent marker of insulin resistance and should trigger intervention to prevent diabetes and heart disease. TG-based screening tests include the Metabolic Syndrome, the TG/HDL-Ratio, and the Hypertriglyceridemic Waist.
In the first phase of our research, we determined that TG-based screening tests failed to detect early cardiometabolic disease in African-Americans and African immigrants to the United States. The major reason for this failure is that in African descent populations, insulin resistance does not trigger hypertriglyceridemia. Thus, TG levels are not a key marker of risk. These TG-based screening tests often diagnose people of African descent as normal at a time when intervention could have delayed or prevented disease. Hence, TG-based screening tests represent a lost opportunity for early intervention and contribute to health disparities. Once we made the observation that TG-based screening tests were not optimally beneficial in African descent populations, we used metabolic testing and mathematical modeling to identify the etiology. Factors that have been uncovered so far include the following findings: African-Americans have high levels of the enzyme lipoprotein lipase, great sensitivity to insulin-induced free fatty acid suppression, and low levels of apoC-III and visceral adipose tissue. We are also exploring whether hyperinsulinemia has a greater impact than insulin resistance on the development of cardiometabolic disease and obesity in African descent populations.
Overall, diabetes and heart disease are the result of both insulin resistance and hyperinsulinemia. But the earliest manifestations may differ by race. In white populations, insulin resistance and hypertriglyceridemia dominate early. Our research suggests that in African-descent populations, hyperinsulinemia may be the initial sign. Elucidating differences in early disease development will lead to the development of better screening tests for everyone. As we work on identifying the best screening tests for cardiometabolic disease in African-descent populations, we are also testing the efficacy of hemoglobin A1C as a screening test for diabetes.