Vitamin D and rickets: much has been accomplished, but there is room for improvement

DNA methylation levels of CYP2R1 and CYP24A1 predict vitamin D response variation

Factors contributing to the variability of serum 25-hydroxyvitamin D [25(OH)D] in response to a given dose of vitamin D supplementation are largely unknown. We examined whether DNA methylation levels of Cytochrome P450 (CYP) enzymes (CYP2R1, CYP24A1, CYP27A1, and CYP27B1) are potential biomarkers predicting vitamin D response variation. We randomized 446 white postmenopausal women to a calcium and vitamin D (1100IU/day) intervention for at least 12 months. From these subjects, 18 with the highest 12-month increase in serum 25(OH)D were selected as "responders." Another 18 with the lowest 12-month increase in serum 25(OH)D were selected as "non-responders." DNA methylation levels between the groups were compared. To validate findings in the first study, association between DNA methylation levels and vitamin D response variation was studied in another 145 extended independent white postmenopausal women. In the first study, compared to non-responders, responders had significantly lower baseline DNA methylation levels in the promoter region of CYP2R1 (8% in the responders vs. 30% in the non-responders, P=0.004), and CYP24A1 (13% in the responders vs. 32% in the non-responders, P=0.001). In the validation study, for CYP2R1, baseline DNA methylation levels at eight CpG sites were negatively associated with 12-month increases in serum 25(OH)D (P<0.05). For CYP24A1, baseline DNA methylation levels at two CpG sites were also negatively associated with vitamin D response variation (r=-0.151, P=0.011; r=-0.131, P=0.025). These negative associations were consistent with the first study's results. Our findings indicate that baseline DNA methylation levels of CYP2R1 and CYP24A1 may predict vitamin D response variation. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Measurement of vitamin D

There are many different methods to choose for vitamin D analysis. While immunoassays are available commercially and readily automated, specificity for 25-hydroxyvitamin D2 and D3 is variable. Chemical assays such as HPLC and LC-MS/MS have greater specificity and are capable of detecting 25-hydroxyvitamin D2 and D3 separately, but are more complex and require method development. Currently LC-MS/MS is considered the method of choice for 25-hydroxyvitamin D analysis and the methods given here are for LC-MS/MS analysis of serum, plasma and dried whole blood for the separate quantitation of 25-hydroxyvitamin D2 and D3. In addition to highlighting potential interferences, the many non-analytical factors that influence vitamin D measurement are also discussed.