The age-associated adiposity and the effect of long-term vitamin D was studied in vitamin D deficient rats. In in vivo experiments, the influence of a 9 months of vitamin D treatment (weekly oral gavage with 0.125 mg vitamin D3 (5000 IU)/100g body weight) on the adipocyte precursors from the omental adipose tissue was examinated. In in vitro experiment, rat adipose-derived mesenchymal stromal/stem cells (ASCs) were induced to differentiate into adipocytes in the presence or absence of 25(OH)D3 (0.25, 25, and 2500 nmol/L). ASCs derived from vitamin D-treated animals showed an increase adipogenic potential as compared to vitamin D-deficient rats. The addition of 25(OH)D3 inhibits the adipocyte differentiation and lipid deposition in a dose dependent manner.