Department of Medicine, Division of Endocrinology, University of California, San Diego, California, USA. Department of Internal Medicine, University of Texas Southwestern, Dallas, Texas, USA. Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, The University of Texas Health Science Center, Houston, Texas, USA. Department of Medicine, Division of Endocrinology, Houston Methodist, Houston, Texas, USA. NASA Johnson Space Center, Houston, Texas, USA. Department of Internal Medicine, University of California Los Angeles-Olive View, Los Angeles, California, USA.