What is the main source of vitamin D for most people?

The main source of vitamin D for most people is sunlight exposure. When the skin is exposed to ultraviolet B (UVB) rays from the sun, it synthesizes vitamin D3 (cholecalciferol), which is then converted into its active form in the liver and kidneys. This natural process is highly effective, and for many individuals, it fulfills their vitamin D requirements without the need for dietary sources or supplementation. While dietary supplements and food sources can contribute to vitamin D intake, the body’s ability to produce it through sunlight is generally the most significant and accessible means for the majority of the population.

Fatty fish and fortified milk products do provide vitamin D, but they typically do not supply sufficient amounts on their own to meet the recommended daily allowance when compared to the body's capacity to generate vitamin D through exposure to sunlight.