Comparison of the Appearance of Radiolabelled Vitamin D₃ and 25-Hydroxy-Vitamin D₃ in the Chylomicron Fraction of Plasma after Oral Administration in Man

1. The uptake of either orally administered [³H]vitamin D₃ or 25-[³H]hydroxy-vitamin D₃ into the chylomicron fraction of plasma was studied in 12 healthy male subjects.

2. The amount of [³H]vitamin D₃ in the chylomicron fraction expressed as a percentage of the total plasma radioactivity was higher than that of 25-[³H]hydroxy-vitamin D₃.

3. It is suggested that the mechanism of intestinal absorption of vitamin D and 25-hydroxy-vitamin D may differ in man, the absorption of 25-hydroxy-vitamin D possibly being less dependent on bile acids.