1. Department of Bio- and food sciences, University College Ghent, B-9000 Ghent, Belgium.
2. Department of Public Health, Faculty of Medicine and Health Sciences, Ghent University, B-9000 Ghent, Belgium.
3. Faculty of Medicine and Health Sciences, Ghent University, B-9000 Ghent, Belgium.
4. General practice Vossensteert Sint-Jozef, B-8000 Bruges, Belgium.