Vitamin D
The fat‑soluble nutrient that supports bone and muscle health.
Vitamin D refers to fat‑soluble compounds, notably vitamin D2 (ergocalciferol) and vitamin D3 (colecalciferol), that the body produces in skin after sunlight exposure and that are also obtained from certain foods and supplements. It facilitates intestinal absorption of calcium and phosphorus and contributes to bone mineralization, normal muscle function and aspects of immune regulation. Deficiency is common in many populations, so dietary sources, fortified foods and supplements are often used to help maintain adequate status.
Supplementation is used to prevent or correct low vitamin D status; commonly cited intake values include 15 µg (600 IU) for people aged one year and older and 10 µg (400 IU) for infants 7–11 months, but individual needs vary with sunlight exposure, diet, age and health conditions. Forms available include D2 and D3 (D3 is frequently used and plant‑derived D3 from lichens is available), in drops, capsules or combined formulas with calcium. Contraindications and safety precautions apply (for example, hypercalcemia and certain medications), and excessive intake can cause adverse effects, so individual assessment and professional guidance are advised.
At a Glance
Fat-soluble secosteroids produced in the skin after UVB exposure and present in certain foods and fortified products. They facilitate intestinal absorption of calcium and phosphorus and contribute to bone mineralization, muscle function and immune regulation.
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Origin & History
Vitamin D originates from two main sources: endogenous synthesis in the skin under ultraviolet B sunlight and intake from a few natural foods and fortified products. Naturally occurring sources include cod liver oil and fatty fish, while dietary availability was later expanded through fortification and a range of supplement formats; the compound exists in several forms, notably D2 and D3, which convert to the active metabolite in the body.
Cod liver oil and similar animal oils were widely administered historically for children with rickets and became a cultural reference point for supporting skeletal development. Early research connected a dietary or sunlight‑related deficiency with the bone disease observed in children, and the term “vitamin of the sun” entered common use as societies adopted both sun exposure and dietary measures; over time, standardized supplements and fortified foods were developed and, more recently, plant‑based D3 options have been introduced for vegetarian and vegan use.
Composition & Active Compounds
Vitamin D describes a group of fat‑soluble secosteroids that occur as crystalline compounds or as oils in supplement preparations; chemically they comprise precursor forms that are converted in the body to an active hormonal metabolite. The main chemical constituents are precursor sterols (commonly called calciferols) and the active form produced by hydroxylation in the liver and kidneys; these different compounds determine biological activity, source (plant, animal or cutaneous synthesis) and use in supplements.
The active metabolite calcitriol (1-25-dihidroxi-vitamina D) is the principal biologically active form derived from precursor vitamin D2 or D3.
- Calciferol: umbrella term for vitamin D compounds
- Ergocalciferol: vitamin D2, typically from plant or fungal sources
- Colecalciferol: vitamin D3, produced in skin and found in animal sources
- 1-25-dihidroxi-vitamina D (calcitriol): the active hormonal form formed after metabolic activation
Properties & Effects
Vitamin D is traditionally known for its role in skeletal development and ongoing bone maintenance, and it is also associated with normal muscle performance and immune activity. Its actions have been the subject of extensive clinical and population research across age groups.
Vitamin D is best documented for supporting bone growth in children and maintaining bone health in adults.
- Bone health: may support normal bone growth in children and maintenance of bone density in adults.
- Muscle function: may support normal muscle performance and help prevent age‑related decline in muscle function.
- Dental health: may support healthy tooth mineralization and dental integrity.
- Immune function: research suggests it may support normal immune system activity and host defenses.
- Mineral balance: may support normal balance of calcium and phosphorus in the body.
- Nervous and clotting functions: may support normal nerve signal transmission and appropriate blood coagulation.
Dosage & How to Use
Common reference intakes and commonly used medical dosing approaches reported in guidance and clinical practice are summarized below.
| Reference intake (≥1 year) | 15 µg (600 UI) for people aged one year and older including pregnant and lactating |
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| Infants 7–11 months | 10 µg (400 UI) per day |
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| Severe deficiency | Higher doses may be administered under medical supervision |
Safety, Side Effects & Contraindications
People with elevated blood calcium (hypercalcemia) or a history of calcium-based kidney stones should avoid vitamin D supplements unless supervised by a healthcare professional. Caution is also advised for those receiving treatment for heart rhythm disorders and for people taking the weight‑loss drug orlistat; professional guidance is recommended in these situations.
Adverse effects are uncommon at recommended intakes but excessive or prolonged intake can cause symptoms such as nausea, headache, muscle and bone pain, cardiac rhythm disturbances and calcium deposits in kidneys and other organs; these outcomes are associated with very high doses. Individual responses vary, so follow dosing guidance and seek medical evaluation and monitoring when high doses are prescribed or when underlying conditions are present.
- Hypercalcemia: contraindicated in people with elevated blood calcium levels
- Calcium-based kidney stones: contraindicated in people with calcium stone formation in the urinary tract
- Arrhythmia treatment: seek professional advice if undergoing treatment for heart rhythm disorders
- Orlistat: seek professional advice if taking orlistat for obesity as it may affect suitability
Consult a healthcare professional before use, especially if you have hypercalcemia, calcium kidney stones, are taking orlistat or medications for arrhythmia, or before high‑dose supplementation.