1. Department of Internal Medicine, Nagayama Clinic , Oyama, Tochigi , Japan
2. Center of Diabetes, Endocrinology and Metabolism, Toho University, Sakura Medical Center , Sakura, Chiba , Japan
3. Japan Health Promotion Foundation , Shibuya-Ku, Tokyo , Japan
4. Department of Internal Medicine, Mihama Hospital , Chiba, Chiba , Japan