CYP2R1 and vitamin D deficiency: To explain these differences, among other factors, women would be more vulnerable to vitamin D deficiency due to the increase in the expression of metabolising genes such as Vdr, Cyp2r1 and Cyp27b1 induced by oestrogens and because of their higher percentage of adipose tissue storing vitamin D. In line with our results, the relationship between vitamin D deficiency and muscle mass and strength seems to be stronger for men than for women [36].