The importance of analyzing the serum C3-epimer level for evaluating vitamin D storage in some special populations.

OBJECTIVE: The serum 25-hydroxyvitamin D [25(OH)D] is recommended by various management agencies for evaluating the nutritional status of vitamin D (VitD). However, 25(OH)D cannot reflect the actual composition and activity of VitD in vivo. This study used UPLC-MS/MS to detect the levels of serum VitD metabolites in some special populations, so as to clarify its importance in accurately evaluating VitD storage in vivo. SUBJECTS AND METHODS: A total of 2029 subjects were enrolled, including 1204 cases in minor health (MH), 467 in the minor disease (MD), 119 in the adult health (AH) and 239 in adult disease (AD). Serum VitD2 and VitD3 levels were measured by UPLC-MS/MS. Serum C3-epi concentrations were also measured in 144 subjects by a spot check method. RESULTS: There were significant differences in the levels of VitD2, VitD3 and 25(OH)D among groups (all p <0.001). According to serum level of 25(OH)D, percentage of subjects with sufficient VitD in the MH, MD, AH and AD group were 65.4%, 52.7%, 29.4% and 20.9%, respectively. After converting VitD2 activity to AVitD3, subjects with sufficient VitD in MH, MD, AH and AD group accounted for 53.2%, 40.9%, 17.7% and 11.3%, respectively. C3-epi levels in the MH (z = 7.49, p <0.001), MD (z = 7.03, p <0.001) and AD group (z = 4.68, p <0.001) were higher than that in the AH group. CONCLUSIONS: Not only the serum 25(OH)D level, but also the simultaneous detection of VitD2 and VitD3 levels will overestimate the VitD storage in some subjects. Accurate evaluation of VitD storage in these individuals also requires detection of C3-epi levels.