We conducted face-to-face interviews with all participants either in the hospital or by visiting their home village. A standardized questionnaire included family history of BEN and, to calculate age at each examination, the date of birth. Hypertension was defined as a systolic blood pressure 140 mm Hg and/or a diastolic blood pressure 90 mm Hg and/or history of hypertension. To identify diabetes, both history of diabetes and serum glucose were used. If the participants reported that they had diabetes within five years preceding the study period, they were defined as diabetic. If the serum glucose was recorded to be >6.2 mmol/L during the previous two years, those participants were also classified as diabetic.