25-Hydroxyvitamin D3 (25(OH)D3) as the metabolite of vitamin D, is connected with various of diseases, and important to people with limited sunshine. Thus, the investigation of serum 25-hydroxyvitamin D and its variation in these people is necessary. In this study, a simple, precise, and accurate method for serum 25(OH)D3 determination by LC/MS/MS was developed. Serum samples were obtained monthly for one year from 11 male and 11 female indoor workers in Sapporo, Japan, and the overall 25(OH)D3 concentration was 12.9 ± 4.7 ng/mL. The 25(OH)D3 in females was significantly lower than that in males (14.0 ± 5.0 vs. 11.9 ± 4.3 ng/mL). The serum 25(OH)D3 concentration in males and females were both strongly correlated to UV-B radiation (r2 = 0.8477 and 0.7384, respectively), with a two-month's lag. Also the monthly change in 25(OH)D3 in males was more significant than that in females.
Keywords: 25-Hydroxy vitamin D3; LC/MS/MS; UV-B; monthly variation.