Can you tell me how the body produce vitamin d?

Enough sunlight: Hi. Humans can make our own vitamin D in the skin upon exposure to UV light in sunlight. This vitamin D (vitamin D3) then has a hydroxyl group (-OH) added on to the 25 position in the liver in an unregulated step, creating 25(OH)vitamin D. This is then converted to the active form, calcitriol by addition of an -OH group at the 1 position in a tightly regulated step (regulated by PTH and FGF-23).