25-OH [D.sub.2] (25-hydroxyergocalciferol
; >98% purity) and 25-OH [D.sub.3] (25-hydroxycholecalciferol; >98% purity) were purchased from Sigma Aldrich.
A competitive protein binding assay for 25-hydroxy-cholecalciferol and 25-hydroxyergocalciferol
 Nonstandard abbreviations: 25(OH)D, 25-hydroxyvitamin D; UV, ultraviolet; 25(OH)[D.sub.2], 25-hydroxyergocalciferol
; 25(OH)[D.sub.3], 25-hydroxycholecalciferol; FDA, Food and Drug Administration; and EDsa median effective dose.
Serum total 25-hydroxyvitamin D (25-hydroxycholecalciferol, D2 and 25-hydroxyergocalciferol
, D3) was assayed in duplicate using a commercial kit (Incstar Inc., Stillwater, MN, USA).