1. Department of Diabetes and Metabolic Diseases, Graduate School of Medicine, The University of Tokyo , Tokyo 113-8655 , Japan
2. Department of Medicine, Ohta Nishinouchi Hospital , Fukushima 963-8558 , Japan
3. Division of General Internal Medicine, Department of Medicine, Tokyo Medical University Ibaraki Medical Center , Ibaraki 300-0332 , Japan
4. Department of Medicine, Fujita Health University , Aichi 470-1192 , Japan
5. Department of General Medicine, Juntendo University Faculty of Medicine , Tokyo 113-8421 , Japan