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)

Background: 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.