1. Gastrointestinal Cancer Research Center; Ardabil University of Medical Sciences; Ardabil; Iran
2. Digestive Disease Research Center; Tehran University of Medical Sciences; Tehran; Iran
3. Non-Communicable Diseases Research Center; Endocrinology and Metabolism Research Institute, Tehran University of Medical Sciences; Tehran; Iran
4. School of Public Health; Tehran University of Medical Sciences; Tehran; Iran
5. Department of Epidemiology; University of Groningen, University Medical Center Groningen; Groningen; The Netherlands