1. University of Oulu, Department of Biology, P.O. Box 3000, FIN-90014 University of Oulu, Oulu, Finland
2. Finnish Institute of Occupational Health, Aapistie 1, FI-90220 Oulu, Finland
3. University of Oulu, Institute of Health Sciences, P.O. Box 5000, FIN-90014 University of Oulu, Oulu, Finland