1. Research Institute of Public Health, School of Public Health and Clinical Nutrition, University of Kuopio, P.O. Box 1627, FI-70211 Kuopio, Finland, Department of Applied Chemistry and Microbiology, P.O. Box 27, Food Chemistry, FI-00014 University of Helsinki, Finland, and Division of Pharmaceutical Biology, Faculty of Pharmacy, P.O. Box 56, FI-00014 University of Helsinki, Finland