The level of vitamin D using the LC–MS/MS method and related factors in healthy Korean postmenopausal women

Aim: The main purposes of the study were (i) to evaluate serum vitamin D concentration in the forms of 25(OH)D₂, 25(OH)D₃ and total 25(OH)D in Korean postmenopausal women using the LC–MS/MS method, which offers increased sensitivity and selectivity; (ii) to determine the relationship between the bone turnover marker, parathyroid hormone (PTH) and 25(OH)D₃, total 25(OH)D separately; and (iii) to determine the factors that may be associated with vitamin D deficiency using body composition analysis and laboratory blood tests. Method: A total of 200 postmenopausal women were recruited from November 2012 to March 2014. To control for seasonal ultraviolet exposure time differences in serum 25(OH)D, laboratory tests were performed only from November to March when vitamin D is not synthesized. Independent relationships between 25(OH)D₃, total 25(OH)D and other variables were assessed by multiple regression analysis. Results: The mean serum 25(OH)D₂, 25(OH)D₃ and total 25(OH)D levels were 0.51 (±0.44) ng/mL, 14.23 (±7.05) ng/mL and 14.69 (±7.13) ng/mL, respectively. Both 25(OH)D₃ and total 25(OH)D were positively correlated with erythrocyte sedimentation rate (ESR), Apo A-I and C-terminal cross-linked telopeptides of type I collagen in Korean postmenopausal women. Both serum 25(OH)D₃ and total 25(OH)D were negatively correlated with alkaline phosphatase, PTH and percent body fat. However, osteocalcin showed a negative correlation (r = −0.451; P = 0.041) with only 25(OH)D₃ and not with total 25(OH)D (r = −0.417; P = 0.064). Conclusion: Both 25(OH)D₃ and total 25(OH)D were negatively correlated with PTH, a bone formation marker (alkaline phosphatase) and percent body fat. Both 25(OH)D₃ and total 25(OH)D were positively correlated with a bone resorption marker (C-terminal cross-linked telopeptides of type I collagen), ESR and Apo A-I after multiple regression analysis.