Waist circumference and glycaemia are strong predictors of progression to diabetes in individuals with prediabetes in sub-Saharan Africa: 4-year prospective cohort study in Malawi

IntroductionSub-Saharan Africa is projected to have the highest increase in the number of people with diabetes worldwide. However, the drivers of diabetes in this region have not been clearly elucidated. The aim of this study was to evaluate the incidence of diabetes and the predictors of progression in a population-based cohort with impaired fasting glucose (IFG) in Malawi. MethodsWe used data from an extensive rural and urban non-communicable disease survey. One hundred seventy-five, of 389 individuals with impaired fasting glucose (IFG) at baseline, age 48 {+/-}15 years and body mass index 27.5 {+/-}5.9 kg/m2 were followed up for a median of 4.2 years (714 person-years). Incidence rates were calculated, and predictors of progression to diabetes were analysed using multivariable logistic regression models, with overall performance determined using receiver operator characteristics (ROC) curves. ResultsThe median follow-up was 4.2 (IQR 3.4 - 4.7) years. Forty-five out of 175 (26%) progressed to diabetes. Incidence rates of diabetes were 62.9 per 1000 person-years 95% CI, 47.0-84.3. The predictors of progression were higher; age (odds ratio [OR] 1.48, 95% CI 1.01-2.19, P=0.046), BMI (OR 1.98, 95% CI 1.34-2.94, P=0.001), waist circumference (OR 2.50, 95% CI 1.60-3.91,P<0.001), waist-hip ratio (OR 1.40, 95%CI 0.98-2.01, P=0.03), systolic blood pressure (OR 1.56, 95% CI 1.10-2.21, P=0.01), fasting plasma glucose (OR 1.53, 95%CI 1.08-2.16, P=0.01), cholesterol (OR 1.44, 95% CI 1.00-2.08, P=0.05) and low-density lipoprotein cholesterol (OR 1.80, 95% 1.23-2.64, P=0.002). A simple model combining fasting plasma glucose and waist circumference was predictive of progression to diabetes (ROC area under the curve=0.79) ConclusionThe incidence of diabetes in people with IFG in Malawi is higher than those seen in Europe (35.0 per 1,000 person-years) but similar to those seen in India (61.0 per 1,000 person-years). Predictors of progression are like those seen in other populations. A simple chart with probabilities of progression to diabetes based on waist circumference and fasting plasma glucose could be used to identify those at risk of progression in clinical settings in sub-Saharan Africa.