Markers Indicating Body Vitamin D Stores and Responses of Liver and Adipose Tissues to Changes in Vitamin D Intake in Male Mice

Circulating 25-hydroxyvitamin D (25(OH)D) is regarded as the most reliable biomarker of vitamin D status. However, limited data exist concerning the suitability of 25(OH)D as an indicator of body vitamin D stores and the ability of adipose tissue to mobilize vitamin D. In the first study, in which male mice received different vitamin D(3) doses for three weeks, we found strong linear response relationships between vitamin D(3) intake and levels of vitamin D(3) in the plasma (p < 0.001), liver (p < 0.001) and adipose tissues (p < 0.001), and strong positive correlations between plasma and tissue stores of vitamin D(3) (p < 0.001). Plasma levels of 25(OH)D(3) and 24,25-dihydroxyvitamin D(3) (24,25(OH)(2)D(3)) showed weak or no correlations with tissue vitamin D(3) stores. Data from a second study demonstrate a strong and rapid response of plasma 25(OH)D(3) in vitamin D(3)-treated mice with a low vitamin D status. Additionally, mice fed a vitamin D-free diet showed a strong and rapid decline in vitamin D(3) in the liver, whereas the decline in different adipose tissues was distinctly lower than that in the liver. To conclude, tissue stores of vitamin D(3) were best reflected by plasma vitamin D(3). In contrast to the liver, adipose tissues responded less sensitively to an absence of vitamin D intake.