1. Epidemiologic Research and Information Center, Veterans Affairs Puget Sound Health Care System, Seattle, WA, USA.
2. Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA.
3. Department of Endocrinology and Metabolism, National Health Insurance Service Ilsan Hospital, Goyang, Korea.
4. Sleep Medicine Section, Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, PA, USA.
5. Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA.
6. Department of Neurology, Chonbuk National University Medical School, Jeonju, Korea.