A few foods naturally contain small amounts of vitamin D. Oily fish such as salmon, mackerel, sardines, and bluefish remain among the richest natural dietary sources. Cod liver oil, although less commonly consumed today, continues to stand out as one of the most concentrated natural sources of vitamin D. The two primary forms of this vitamin—vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol)—occur naturally in different sources: D₂ is typically found in yeast and some fungi, while D₃ is abundant in fish liver oils. Small amounts of vitamin D can also be found in vegetables, meat, and egg yolks, but these contributions are minimal.
Because natural food sources are limited, many countries rely on fortified foods to help prevent vitamin D deficiency. Milk has become the most practical carrier because it is widely consumed and easy to enrich with crystalline vitamin D. Other fortified products may include breakfast cereals, margarine, and plant-based milk alternatives.
Despite the value of dietary and fortified sources, the most efficient source of vitamin D is sunlight. When skin is exposed to ultraviolet-B (UVB) radiation, it converts a naturally occurring pro-vitamin into vitamin D₃, which the kidneys can later activate. For most healthy individuals, sunlight can provide 90–100% of their vitamin D requirement, depending on skin type, geographic location, and time spent outdoors. Like other fat-soluble vitamins, sunlight-derived vitamin D can be stored in the liver for future use.
Vitamin D supplements offer another important option, especially for individuals with limited sun exposure. Many multivitamins contain around 400 IU of vitamin D, while higher-dose preparations—sometimes up to 50,000 IU—are available under medical supervision for treating deficiencies.
Natural Sources of Vitamin D
