1. Medical Sciences, Faculty of Medicine, University of Tsukuba, Tsukuba 305-8575, Japan
2. Department of Nutrition, Tsukuba Memorial Hospital, Tsukuba 300-2622, Japan
3. Division of Laboratory Medicine, Tsukuba University Hospital, Tsukuba 305-8576, Japan
4. Division of Gastroenterology, Faculty of Medicine, University of Tsukuba, Tsukuba 305-8575, Japan