The primary source of vitamin D is sunlight. Specifically, when the skin is exposed to ultraviolet B (UVB) rays from the sun, it synthesizes vitamin D. This essential nutrient plays a crucial role in calcium absorption, bone health, and immune function. In addition to sunlight, vitamin D can also be obtained from certain foods, such as fatty fish (like salmon and mackerel), fortified dairy products, and egg yolks. Supplements are also available for those who may have difficulty getting enough vitamin D from sunlight or dietary sources, particularly in regions with limited sun exposure.