Prevalence and risk factors for diabetes and diabetic retinopathy: results from the Nigeria national blindness and visual impairment survey (BMC Public Health)

Background: In Nigeria, rapid urbanisation and increasing life expectancy are likely to increase the incidence of non-communicable diseases (NCD), including diabetes. As the epidemic of diabetes matures visual loss from diabetic retinopathy (DR) will increase unless mechanisms for early detection and treatment improve, and health systems respond to the growing burden of NCDs. We report findings in relation to diabetes and diabetic retinopathy from the Nigeria National Blindness and Visual Impairment cross-sectional Survey of adults aged >=40 years (2005-2007). Methods: A cross-sectional population-based sample of 13,591 participants selected by multistage stratified cluster random sampling with probability-proportional-to-size procedures were examined in 305 clusters across the country between January 2005 to June 2007 (30 months). All were asked if they were previously diagnosed to have diabetes by a doctor. Presenting distance visual acuities were measured in each eye using a logMAR E chart and all underwent a basic eye examination by an ophthalmologist. Height, weight and blood pressure were measured. Participants with visual acuity 11.1 mmol/l or DR was detected. Data in the subsample were used to estimate the prevalence of diabetes, and to analyse risk factors for diabetes and DR using multivariable logistic regression. Additional information on the types of DR was obtained from the other participants not in the subsample. Results: In the subsample, 164/1,759 participants were excluded due to missing data (on diabetes history, retinal examination and RBG result), leaving 1,595 for analysis. 52/1,595 had diabetes giving a prevalence of 3.3% (95%CI 2.5-4.3%). 25/52 (48%) of those defined as diabetic did not know they had diabetes (new diabetics). In eight diabetics media opacity precluded retinal examination. Nine diabetics had DR (9/44 [20.5% overall]; 25% [6/24] of previously diagnosed diabetics; 15% [3/20] of new diabetics). Higher prevalence of diabetes was associated with urban residence (Odds ratio [OR] 1.87) and being overweight/obese (OR 3.02/4.43 respectively). Although not statistically significant, DR was associated with hypertension (OR 3.49) and RBG > 15.0 mmol/L (OR 8.10). Persons with diabetes had 3 times greater odds of blindness. In the 11,832 other participants in the study sample, 175 (1.5%) had a history of diabetes and 28 had DR. Types of DR (total = 37) were proliferative (10.8%) and macular oedema (51.4%). Conclusion: The overall age-adjusted prevalence of diabetes mellitus in Nigeria was 3.25% (95%CI 2.50-4.30) and over 10% of people with diabetes aged >40 years had sight-threatening DR. These data will enable the development of better public health strategies for the control of diabetes and planning services for DR to prevent vision loss.