Definitions
The cutoff values of serum 25-hydroxyvitamin (OH)-D 75, 50, and
25 nmol/L were used to define insufficiency (VDI), deficiency, and severe vitamin deficiency (sVDD), respectively [12,13]. To convert values of 25-OH-D concentration from conventional (ng/mL) to the International System of Unit (nmol/L), we multiplied by factor 2.496 [14].