1. Medical Research Unit in Clinical Epidemiology of the Mexican Social Security Institute, Chihuahua, Mexico
2. Graduate Program in Biotechnology, Faculty of Chemical Sciences, Autonomous University of Chihuahua, Apdo. Postal 1542-C, Chihuahua, Mexico
3. Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
4. Medical Research Unit in Clinical Epidemiology of the Mexican Social Security Institute, Chihuahua, Mexico,