Briefly, the study population was selected from four urban districts (Guro, Yangcheon, Gwanak and Gangseo) located in the south-west area of Seoul. A total of 1737 apparently healthy individuals (between 60 and 92 years of age) eventually participated in this survey starting in 1999. A follow-up examination was performed in 2002, and an additional 873 subjects who had not participated in the first examination were newly recruited.