Insulin resistance, beta cell function and cardiovascular risk factors in Ghanaians with varying degrees of glucose tolerance

Abstract

Objective: Type 2 diabetes is characterized by beta cell dysfunction and insulin resistance (IR). The disease is associated with high rates of cardiovascular mortality and morbidity. Recently, the American Diabetes Association Expert Committee recommended the measurement of fasting glucose as a tool for screening and diagnosing diabetes, in order to identify patients with a mild form of the disease as well as to enhance the detection of undiagnosed type 2 diabetes. The significance of these criteria with respect to cardiovascular risk factors in native Ghanaians is unknown. The objectives of the present study were to examine the cardiovascular risk factors in a sample of native Ghanaians with varying degrees of glucose intolerance as defined by fasting glucose levels as specified by the ADA criteria.

Research and methods: The population consisted of 200 indigenous Ghanaian subjects, age range 25-74 years, residing in the Accra metropolitan areas. Subjects were categorized using the fasting plasma glucose (FPG) alone as normal fasting glucose (NFG, FPG < 110 mg/ dL), impaired fasting glucose (IFG, 11 < FPG 126 mg/dL), and diabetic (DM, FPG > 126 mg/ dL). Anthropometric parameters (blood pressure, waist circumference and waist-hip circumference ratios) were measured in each subject. Levels of serum glucose, c-peptides and insulin were measured at baseline and after 2 hours of oral glucose challenge. Insulin resistance (HOMA-IR) and beta cell function (HOMA-%B) were assessed by homeostasis model assessment (HOMA). Levels of fasting serum cholesterol, high-density lipoprotein cholesterol (HDL-C), cholesterol, and triglycerides were measured in each subject.

Results: There were 181 subjects in the NFG category, 11 in the IFG category, and 8 newly diagnosed type 2 diabetic subjects. The mean age, BMI, waist circumference (WC), and WHR did not differ between the 3 groups. The mean fasting glucose and the corresponding 2-hour glucose levels rose with the worsening of glucose tolerance. Similarly, the means for serum fasting, post-challenge serum insulin, and c-peptide levels were significantly greater in the IFG and DM groups. Fasting serum cholesterol and high density lipoproteins did not differ statistically between the 3 groups, However, the means for serum triglycerides were greater in the IFG and DM groups when compared to the NFG group. The insulin resistance (IR) as assessed by HOMA was 2x and 4x greater in the IFG (3.76) and DM (6.12) groups when compared with the NFG (1.82, P < .05).

Conclusions: We have characterized the metabolic and anthropometric risk factors for CVD in native Ghanaians with varying degrees of glucose tolerance, as defined by the ADA criteria. We found that both IFG and DM were associated with beta cell dysfunction, insulin resistance, and elevated serum triglycerides. However, the well established cardiovascular risk factors, such as body mass index, body fat distribution, and blood pressure did not track with the increasing glucose intolerance in the native Ghanaians. We conclude that the Ghanaian patients with IFG and type 2 diabetes were non-obese and exhibited severe beta cell dysfunction, insulin resistance, and elevated triglycerides, but none of the other conventional risk factors, at the time of diagnosis. Future research should focus on the sequential changes in risk factors during development of cardiovascular diseases in native Ghanaians with varying degrees of glucose tolerance.