1. Faculty of Medicine, University of Valladolid, Avenida Ramón y Cajal, 7, 47005 Valladolid, Spain
2. Castilla y León Cystic Fibrosis Unit, University Clinical Hospital of Valladolid, Avenida Ramón y Cajal, 3, 47005 Valladolid, Spain
3. Science Faculty, University of Cadiz, Paseo de Carlos III, 28, 11003 Cádiz, Spain
4. Department of Chemistry, Science Faculty, University of Burgos, Plaza Misael Bañuelos s/n, 09001 Burgos, Spain
5. Department of Pediatrics of the Faculty of Medicine, University of Valladolid; Section of Gastroenterology and Pediatric Nutrition, University Clinical Hospital of Valladolid, Avenida Ramón y Cajal, 7, 47005 Valladolid, Spain