Figure 4.

Principles of determining the vitamin D response index. Data are analyzed by relating the changes in the expression of vitamin D target genes at day 1 (d1) and day 0 (d0) to the ratio of the 25(OH)D₃ serum levels at d1 and d0 (A). In this way, the response of the target genes is calculated comparably to in vitro studies [23]. The responsiveness of each the study participants is scored for every selected vitamin D target gene as no (red), weak (yellow) or strong responders (green) (A). The sums of the scores of all tested genes is ranked and the individuals are segregated by the method k-means into low, mid and high responders [44] (B).