What vitamin is primarily obtained from sunlight?

The vitamin primarily obtained through sunlight is vitamin D. Human skin can make vitamin D3 when ultraviolet B (UVB) radiation from sunlight acts on a cholesterol-related compound called 7-dehydrocholesterol.

The skin first produces previtamin D3, which spontaneously changes into vitamin D3, also called cholecalciferol. The liver and kidneys then carry out further chemical steps that produce the biologically active hormone calcitriol. Vitamin D helps the body absorb calcium and phosphate, supporting bones, muscles, and normal cellular functions.

Sunlight does not provide vitamin D directly like a food does; it triggers production inside the skin. UVB does not pass effectively through ordinary window glass, and factors such as darker skin pigmentation, clothing, latitude, season, age, and limited outdoor exposure can reduce production. Dietary sources include oily fish, egg yolks, fortified foods, and supplements. Excessive sun exposure is not a safe substitute for balanced nutrition because ultraviolet radiation also raises skin-cancer risk.