Department of Medicine, Division of Endocrinology, Leiden University Medical Center, Leiden, Zuid-Holland, The Netherlands. Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center, Leiden, Zuid-Holland, The Netherlands. Department of Epidemiology, Leiden University Medical Center, Leiden, Zuid-Holland, The Netherlands. Department of Medicine, Division of Endocrinology, Leiden University Medical Center, Leiden, Zuid-Holland, The Netherlands E.J.P.de_Koning@lumc.nl.