The 25-hydroxyvitamin D₃ C-3 epimer: Distribution, correlates, and reclassification of 25-hydroxyvitamin D status in the population-based Atherosclerosis Risk in Communities Study (ARIC)

Little is known about the vitamin D3 epimer [3-epi-25(OH)D3], particularly in adults. We describe characteristics of the D3 epimer within the community-based ARIC cohort. Methods: The vitamin D3 epimer, 25(OH)D₃, and 25(OH)D₂ were measured using LC-MS/MS in stored serum collected in 1990-1992 from 9,887 white and 3,221 black ARIC study participants, aged 46-70years. Cross-sectional characteristics were explored. Results: Concentrations of the epimer were quantifiable (≥1.41ng/ml) in 33.4% of whites and 15.0% of blacks and made up on average 3.23% and 2.25% of total D3 [epimer+25(OH)D₃] concentrations, respectively. Epimer levels were positively correlated with 25(OH)D₃ in both whites (r=0.54) and blacks (r=0.36) and were unrelated to 25(OH)D₂ concentrations. Overall, epimer levels were associated with participant characteristics in a manner similar to that typically observed for 25(OH)D₃. Including the epimer in the calculation of total 25(OH)D resulted in approximately 2% of participants being reclassified from being clinically 25(OH)D deficient to having suboptimal levels. Conclusions: Low concentrations of the D3 epimer were present in adult serum and overall the epimer concentration is moderately correlated with the 25(OH)D₃ concentration. The reclassification of participant's clinical 25(OH)D status upon inclusion of the epimer was minimal.