1. Vitamin Bioavailability Laboratory, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston 02111
2. Department of Gastroenterology, Stiftsklinik Augustinum, München, D-81375, Germany
3. Division of Gastroenterology, Department of Medicine, St. Michael's Hospital and University of Toronto, Toronto, ON, M5S 1A8, Canada
4. Department of Medicine, Salem Hospital, University of Heidelberg, Heidelberg, 69121, Germany
5. Divisions of Gastroenterology and Clinical Nutrition, Department of Medicine, New England Medical Center, Tufts University School of Medicine, Boston 02111