|ISSN No. 1606-7754 Vol.13 No.2 August 2005|
Total insulin output is low in type-2 diabetic Nigerians
Adamu G Bakari, Geoffrey C Onyemelukwe
Department of Medicine, Ahmadu Bello University & Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
Background: Plasma insulin levels among type 2 diabetic patients are modulated by racial and ethnic factors. In contrast to the plethora of reported studies on plasma insulin levels among type 2 diabetic patients in technically advanced regions of the world, there is paucity of such information in Africa in general. Objective: To study insulin output among type 2 diabetic Nigerians. Subjects and methods: Forty type-2 diabetic and 36 healthy subjects underwent a standard oral glucose tolerance test (OGTT). Fasting and post OGTT plasma insulin levels were measured using an ELISA technique. Integrated insulin responses were calculated using trapezoidal estimation to compute total insulin output. Student’s t test was used to compare means; the level of statistical significance in each case was taken as p < 0.05. Results: The age and sex distribution of diabetic patients and control subjects were similar (p >0.5). Average duration of diabetes was 5.6 ± 4.3 years (range 1 -20 years) Total insulin output was significantly lower among type 2 diabetic patients than in control subjects (360 ± 82.1 micro-units per ml and 745.1 ± 109.0 micro-units per ml respectively P<0.00 1). Conclusion: Type-2 diabetic patients in this study exhibit hypoinsulinaemia; this could be the explanation for the pattern of diabetic complications among type 2 diabetic Nigerians observed in previous studies.
Key words: BMI, Obesity, Nigerians, Type-2 diabetes, WHR
Both hypoinsulinaemia and hyperinsulinaemia have been reported among type 2 diabetic patients1,2 and more importantly, some of the chronic complications of diabetes mellitus are related to prevailing plasma insulin levels.3 Racial factors seem to play modulatory roles in these diverse responses. In South Africa for example, type 2 diabetic Africans exhibit lower plasma insulin levels compared to their Indian counterparts4. The few studies on plasma insulin levels in Nigeria concentrated on healthy volunteers and relatives of type 2 diabetic patients.5,6 There is as yet no reported study of the plasma insulin pattern in Nigerian type 2 diabetic patients as opposed to the vast literature on the subject in technically more developed countries. We studied the total insulin output in response to a standard OGTT among type 2 diabetic patients.
Patients and methods
All patients and control subjects studied were drawn from a single ethnic group (Hausa-Fulani) around the city of Zaria (located at Longitude 08° 30° East and latitude 04° 00° North) in Northern Nigeria. Type 2 diabetic patients attending the diabetic clinic of Ahmadu Bello University Teaching Hospital (ABUTI-1) Zaria and having ‘good’ glycaemic control, defined as fasting blood sugar (FBS) of 4.4 to 6.7 mmol/L, and or a 2 hour post prandial blood sugar of 4.4 to 8.9 mmol/L and ‘acceptable’ glycaemic control (FBS of 6.7 to 7.8 mmol/L and or 2 HPP of 8.9 to 10.0 mmol/L)7 on at least three clinic visits while on dietary therapy alone, or dietary therapy in addition to oral anti-diabetic agent(s), formed the subjects of this study. Classification of patients as type 2 diabetic was however, based on clinical grounds of non-dependence on insulin for survival.8 The exclusion criteria were insulin dependence, evidence of secondary diabetes, current insulin therapy, previous history of ketosis, pregnancy or use of oral contraceptives, and clinical or biochemical evidence of disease of the liver, kidney or thyroid.
Thirty-six healthy volunteers who had no personal or family history of diabetes mellitus or hypertension were recruited to serve as controls. The exclusion criteria were clinical evidence of any illness, personal or family history of diabetes mellitus or hypertension, and current use of any form of medication.
Information on age, sex and anthropometric measurements were obtained from all patients and control subjects. Weights (in Kilograms) were taken with the patients wearing only undergarments to the nearest 0.5 kg. Heights (in metres) were taken to the nearest 0.5 cm with subjects standing erect without shoes or headgear. Body Mass Index (BMI) was derived by dividing the weight by the square of the height.9