1. Institute of Community Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan
2. Foundation for Advancement of International Science, Bio-Laboratory, Tsukuba, Ibaraki, Japan
3. Tsukuba Diabetes Center, Kawai Clinic, Tsukuba, Ibaraki, Japan
4. Department of Endocrinology, Tenri Hospital, Tenri, Nara, Japan
5. Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan