Selective monitoring of vitamin D2 and D3 supplementation with a highly specific 25-hydroxyvitamin D3 immunoassay with negligible cross-reactivity to 25-hydroxyvitamin D2.

Background: The effects of vitamin D2 and D3 supplementation on circulating concentrations of 25(OH)D3 require reliable analytical tools for specific determination of 25(OH)D3 and 25(OH)D2. We have developed a highly specific 25-OH Vitamin D3 ELISA with negligible cross-reactivity towards 25(OH)D2.
Methods: 25(OH)D3 concentrations were measured in several study participants; 1) 641 healthy men and women; 2) 39 postmenopausal women receiving 400-800 IU vitamin D3 daily for 4 months; 3) 45 men and women with hip fracture receiving 1000 IU vitamin D2 daily for 3 months.
Results: This 25-OH Vitamin D3 ELISA had minimal cross-reactivity to 25(OH)D2, (0.7%), and demonstrated a high correlation (r2 = 0.93) with 25(OH)D3 determined by HPLC. 25(OH)D3 increased by 14% in subjects receiving vitamin D3 for 4 months (p < 0.01), whereas there was no significant change in 25(OH)D3 levels in those receiving vitamin D2.
Conclusions: We report that 25(OH)D3 ELISA was used for evaluation of 25(OH)D3 concentrations in subjects receiving vitamin D2 and D3 supplementation. The increase of 25(OH)D3 in circulation with vitamin D3 supplementation and lack of increase with vitamin D2 supplementation suggest that this assay has sufficient sensitivity and specificity to be used as a reliable measurement of nutritional vitamin D3 status in humans.