Representative of the summer-winter 25(OH)D variability at baseline
Roche Diagnostics vitamin D total assay and an ECLIA protein-binding assay for capturing both 25(OH)D3 and 25(OH)D2; Cobas e601 Roche Diagnostics instrument
Analyses repeated on frozen serum from subsequent examination, baseline (+) 6 years
a represents the number of subjects that were assessed both at baseline and at reanalysis (substudy I and II) or the number of subjects assessed only at reanalysis (substudy III).