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.