The Ragama MOH administrative area is situated approximately 18 km north of Colombo, the commercial capital of Sri Lanka. Ragama is a bustling urban township with a multi-ethnic population. Participants of the RHS were resident adults, originally selected by age-stratified random sampling from electoral lists. The cohort was initially screened in 2007, when participants were aged 35–64 years, and was invited back for re-evaluation after 7 years, when participants were aged 42–71 years, in 2014.
In 2007 and 2014 all participants were assessed using a structured interview. They underwent clinical assessment and anthropometric measurements, ultrasound scanning of the liver was done and biochemical and serological tests were undertaken. Further details regarding the screening of the inception cohort are described elsewhere13. The follow up cohort was interviewed by trained personnel to obtain information on socio-demographic variables and lifestyle habits, including diet, alcohol consumption and physical activity. Medical records of subjects, whenever available, were analysed to obtain more details. Blood pressure (BP) and anthropometric parameters including height, weight and waist circumference (WC) were measured. Change in WC was classified as reduction > 5%, between reduction ≤ 5% and increase < 5% (no change) and increase ≥ 5%. Change in weight was classified as loss > 5%, loss ≤ 5% and gain < 5% (no change), gain ≥ 5% and gain ≥ 10%. Total body fat (TBF) and visceral fat percentage (VFP) were measured by a body composition monitor using bioelectrical impedance method (Omron HBF-362 body composition monitor, Omron Healthcare, Lake Forrest, Illinois, United States). Abnormal TBF was defined as > 32% for females and > 25% for males. Abnormal VFP was defined as > 10% for both genders14.
A10-mL sample of venous blood drawn from each participant was used to determine fasting serum triglycerides (TG), high density lipo-proteins (HDL), glycosylated hemoglobinA1c (HbA1c), hepatitis B surface antigen (HBsAg) and anti-hepatitis C virus antibodies (anti-HCV). Hepatitis serological tests were done using CTK Biotech ELISA kits. All participants also underwent ultrasonography of the liver with a 5-MHz 50 mm convex probe (MindrayDP-10 Ultrasound Diagnostic Systems, Mindray Medical International Limited, Shenzhen, China). The ultrasound examination was carried out by medical personnel specially trained in liver ultrasonography. Non-alcoholic fatty liver disease (NAFLD) was diagnosed on established ultrasound criteria for fatty liver (two out of the following three criteria: increased echogenicity of the liver compared to kidney and spleen, obliteration of the vascular architecture of the liver and deep attenuation of the ultrasonic signal), safe alcohol consumption (Asian standards of < 14 units/week for men and < 7 units/week for females) and absence of hepatitis B and C markers15.
Data were entered in Epi Info 7 (Centres for Disease Control and Prevention, Atlanta, GA, USA) and logical and random checks were done. Statistical analysis was done using SPSS ver. 22.0 (SPSS, Chicago, IL, USA). Prevalence and incidence rates with 95% confidence intervals were calculated using standard formula for proportion estimates. Continuous and categorical data were described using median with interquartile range (IQR) and frequencies with percentages, respectively. Group comparisons were done using Mann Whitney U test and Pearson’s Chi-square-test, for continuous and categorical variables, respectively.
Multiple linear logistic regression models were used to investigate the associated variables with incident DM. The following exposure variables in 2007 were investigated for association with incident DM: gender, age, educational level (i.e. less than General Certificate of Education Ordinary Level), income (i.e. less than median income in the cohort), unsafe alcohol use, smoking pack years, PDM, central obesity (waist circumference ≥ 90 cm for males and ≥ 80 cm for females), raised blood pressure (systolic BP ≥ 140 or diastolic BP ≥ 90 mmHg, or treatment of previously diagnosed hypertension), low HDL [< 40 mg/dL (1.03 mmol/dL) in males and < 50 mg/dL (1.29 mmol/dL) in females, or on specific treatment for this lipid abnormality], raised TG [≥ 150 mg/dL (1.7 mmol/L) or on specific treatment for this lipid abnormality], dyslipidemia (total cholesterol > 140 mg/dL, raised TG, raised HDL or on lipid-lowering therapy), NAFLD and percentage gain in body mass index (BMI), weight and waist circumference. Stepwise variable selection method was adopted to develop the final models. P < 0.05 was considered as significant.
All participants were enrolled after obtaining informed written consent. Ethical approval for the study was obtained from the Ethical Review Committee of the Faculty of Medicine, University of Kelaniya, Ragama, Sri Lanka.