We studied 70 non diabetic Cameroonians (33 males and 37 females) aged 42 ± 10.6 years. All participants had a stable weight (< 5% variation) over 3 months prior to the study. Individuals were excluded from the study if they had physician – diagnosed diabetes, fasting blood glucose concentration > 1.25 g/L, any ongoing disease except well-controlled hypertension, or if they were currently receiving medications known to affect glucose and/or lipid metabolism. We performed all measurements at the National Obesity Centre, Yaoundé, starting between 8 and 10 AM after a 10 to 12-hour overnight fast. Participants were advised to avoid intense physical activity the day prior to, and on the day of the investigation and to have their last meal comprising 50–55% carbohydrates not later than 8 PM the day preceding investigations.
Weight was measured to the nearest 0.1 kg (SECA, Germany). Height was measured to the nearest 0.5 cm using a wall – mounted stadiometer. BMI was calculated as weight (in kg) divided by the square of the height (in metres). Waist circumference was measured to nearest 1 cm at the level of the umbilicus (L4 - L5) and at the end of expiration with the subject upright and his/her hands by the side. Percentage body fat and total fat mass were measured by bioelectric impedance analysis (OMRON BF 302, OMRON Matsusaka Co., Ltd. Japan). For each parameter, 2 measurements were taken and the average used in the analysis.
In all the subjects we collected two fasting venous blood samples from an antecubital vein for the determination of circulating glucose, insulin and adiponectin levels. In a representative sub sample of 16 subjects, we performed a 120-min euglycaemic hyperinsulinaemic clamp at 80 mU/min/m2 insulin infusion rate in order to measure whole body insulin sensitivity. Fasting insulin sensitivity indices were derived from fasting insulin and glucose measurements and were compared to the clamp measurements and yielded the following correlation coefficients: Fasting insulin (r = -0.70; p = 0.008), HOMAIR (r = -0.76; p = 0.004) and QUICKI (r = 0.67; p = 0.01) Glucose/Insulin (r = 0.50; p = 0.06). HOMA had the highest correlation coefficient with clamp-measured whole body insulin sensitivity and was therefore used as surrogate of insulin sensitivity in the study population.
Plasma glucose concentration was determined using the glucose oxidase method. Adiponectin and insulin levels (intra-assay CV = 1.78–6.21%) were determined by RIA (Linco Research Inc, St Charles, MO, USA) at the St-Louis University Hospital, Department of Hormonal Biology, Paris. Adiponectin and insulin were measured on serum samples that had been stored at -80°C for 2–4 months and shipped in thermo boxes on dry ice. All assays were run in duplicate.
Statistical analyses were performed using the Statistical Package for Social Sciences, SPSS® for Windows, Version 12. Results are expressed as frequencies or mean ± SD unless otherwise stated. Comparison across groups was done using one-way analysis of variance (ANOVA) with further group-to-group comparison using the non-parametric Mann-Whitney U test. Correlations between variables was analysed using the non-parametric Spearman Rank Order Test. Linear regression analysis was used to determine independent predictors of serum adiponectin levels.
The study protocol was approved by the Review Committee of the Faculty of Medicine and Biomedical Sciences, University of Yaoundé 1, Cameroon. The study was conducted according to the principles expressed in the Declaration of Helsinki, and written informed consent was obtained from all participants.