1 Department of Public and Occupational Health, VU University Medical Centre, van der Boechorststraat 7, 1081 BT Amsterdam, Netherlands h.merten@vumc.nl.
2 Department of Internal Medicine, VU University Medical Centre, De Boelelaan 1117, 1081 HV Amsterdam, Netherlands.
3 Department of Public and Occupational Health, VU University Medical Centre, van der Boechorststraat 7, 1081 BT Amsterdam, Netherlands.