Vitamin D is a fat-soluble vitamin and prohormone that is essential for overall health. Here are the key points about vitamin D:

1. Functions:

   • Calcium Absorption and Bone Health: Vitamin D helps the body absorb calcium, vital for bone formation and health¹.
   • Muscle Function: It supports muscle function and movement².
   • Immune System: It enhances immune system function, helping the body to fight off infections¹.

2. Sources:

   • Sunlight: The primary natural source is the sun. The skin synthesizes vitamin D when exposed to ultraviolet (UV) rays³.
   • Food: Few foods naturally contain vitamin D. They include fatty fish (e.g., salmon, mackerel), beef liver, cheese, and egg yolks. Some mushrooms provide vitamin D when exposed to UV light³.
   • Fortified Foods: Many foods like milk, orange juice, and cereals are fortified with vitamin D³.

3. Supplementation:

   • Forms: Vitamin D supplements are available as vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Both forms are effective but differ slightly in their structure⁴.
   • Recommendation: Supplements may be needed for individuals who do not get enough vitamin D from sunlight or diet⁵.

4. Deficiency:

   • Causes: Lack of exposure to sunlight, inadequate dietary intake, certain medical conditions, and skin pigmentation can lead to deficiency¹⁵.
   • Health Issues: Deficiency can result in weakened bones, rickets in children, and osteoporosis in adults³.

5. Risks from Excessive Vitamin D:

   • High intakes can lead to hypercalcemia (excess calcium in the blood), which may cause nausea, vomiting, weakness, and kidney damage⁶.

Footnotes

1. Vitamin D: MedlinePlus Medical Encyclopedia ↩ ↩² ↩³

2. Vitamin D: Office of Dietary Supplements ↩

3. Overview of Vitamin D - Dietary Reference Intakes for Calcium and Vitamin D - NCBI Bookshelf ↩ ↩² ↩³ ↩⁴

4. Vitamin D: MedlinePlus Medical Encyclopedia ↩

5. Vitamin D: Benefits, deficiency, sources, and dosage ↩ ↩²

6. Office of Dietary Supplements - Vitamin D ↩