skin 7-dehydrocholesterol Ultraviolet light Provitamin D3 food Vitamin d (an inactive form) In the Liver Hydroxylation In the 25-hydroxy vitamin D3 kidneys: Hydroxylation 1, 25-hydroxy vitamin D3 (active form) Vitamin D Synthesis and ActivationProvitamin D3 Ultraviolet light In the skin: 7-dehydrocholesterol Vitamin D3 (an inactive form) 25-hydroxy vitamin D3 Hydroxylation In the Liver: foods 1, 25-hydroxy vitamin D3 (active form) Hydroxylation In the kidneys: Vitamin D Synthesis and Activation