1 Gastroenterology Unit, Clinical and Translational Epidemiology Unit, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts; Clinical Epidemiology Unit, Department of Medicine Solna, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
2 Department of Medical Epidemiology and Biostatistics, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.