Vitamin D is the vitamin produced when a person is exposed to sunlight. Specifically, ultraviolet B (UVB) rays from the sun initiate the conversion of 7-dehydrocholesterol in the skin into vitamin D3 (cholecalciferol), which is then processed by the liver and kidneys to form the active hormone calcitriol. Vitamin D is essential for maintaining healthy bones and teeth, as it helps regulate calcium and phosphate in the body. It also plays a role in immune function. Due to factors like geographic location, skin color, and lifestyle, many individuals may require dietary supplements or increased sun exposure to meet their vitamin D needs.