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VDBP, total, non-bioavailable, bioavailable, and free 25(OH)D concentrations by season and month of blood draw, and VDBP genotype. (a) By season of blood draw (spring: March, April, and May; summer: June, July, and August; autumn: September, October, and November; winter: December, January, and February). (b) By month of blood draw. (c) By VDBP genotype. Abbreviations: VDBP: vitamin D binding protein.
