1. Department of Internal Medicine, Graduate School, Yonsei University College of Medicine, Seoul, Korea.
2. Center for Health Promotion, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
3. Division of Gastroenterology, Department of Internal Medicine, Yonsei Institute of Gastroenterology, Yonsei University College of Medicine, Seoul, Korea.
4. Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea.