Evidence that vitamin D3 increases serum 25-hydroxyvitamin D more efficiently than does vitamin D2 1–3

Abstract: In all species tested, except humans, biological differences between vitamins D2 and D3 are accepted as fact. To test the presumption of equivalence in humans, we compared the ability of equal molar quantities of vitamin D2 or D3 to increase serum 25-hydroxyvitamin D [25(OH)D], the measure of vitamin D nutrition. Subjects took 260 nmol (<4000 IU) vitamin D2 (n = 17) or vitamin D3 (n = 55) daily for 14 d. 25(OH)D was assayed with a method that detects both the vitamin D2 and D3 forms. With vitamin D3, mean (±SD) serum 25(OH)D increased from 41.3 ± 17.7 nmol/L before to 64.6 ± 17.2 nmol/L after treatment. With vitamin D2, the 25(OH)D concentration went from 43.7 ± 17.7 nmol/L before to 57.4 ± 13.0 nmol/L after. The increase in 25(OH)D with vitamin D3 was 23.3 ± 15.7 nmol/L, or 1.7 times the increase obtained with vitamin D2 (13.7 ± 11.4 nmol/L; P = 0.03). There was an inverse relation between the increase in 25(OH)D and the initial 25(OH)D concentration.