What vitamin is synthesized by the skin upon exposure to sunlight?

What vitamin is synthesized by the skin upon exposure to sunlight? The skin synthesizes vitamin D, specifically vitamin D3, when exposed to ultraviolet B radiation.

UVB light triggers a chemical reaction involving 7-dehydrocholesterol in skin cells. This first forms previtamin D3, which then changes into cholecalciferol, the scientific name for vitamin D3. The liver and kidneys further process vitamin D into forms that help the body use calcium and phosphate.

Vitamin D supports bone mineralization and plays important roles in calcium balance and immune function. It is unusual among vitamins because the body can manufacture it under suitable conditions, although dietary sources, fortified foods, and supplements can also provide it. Vitamin D2, or ergocalciferol, is another form commonly obtained from fungi and fortified foods.

Sunlight through ordinary window glass is not an effective source because glass blocks most UVB. Season, latitude, skin pigmentation, age, clothing, sunscreen, and time spent outdoors all affect production. Sun exposure should not be increased recklessly: ultraviolet radiation also damages skin and raises skin-cancer risk.