Final answer:
Vitamin D is formed in the skin when it is exposed to sunlight. It is important for the absorption of calcium and phosphorous, which are necessary for healthy bones.
Step-by-step explanation:
Vitamin D is formed in the skin when it is exposed to sunlight. The epidermal layer of human skin synthesizes a form of vitamin D3 called cholecalciferol when exposed to UV radiation. This cholecalciferol is then converted to calcidiol and calcitriol, which are the active forms of vitamin D. Vitamin D is important for the absorption of calcium and phosphorous, which are necessary for healthy bones.