Vitamin (D3)
Collective term (D group) for fat-soluble, photosensitive sterol derivatives; in particular vitamins D2 and D3 and - as their natural provitamins - ergosterol and 7-dehydrocholesterol, from which they are produced in the skin under UV exposure; 25-hydroxycholecalciferol is formed in the liver and 1,25-dihydroxycholecalciferol (calcitriol, the most effective metabolite) is formed in the kidney. Stored in the body; daily requirement 2-10 μg; in case of overdose (D-Hypervitaminos). Deficiency leads to mineralisation disorders, rickets in infants and young children, osteomalacia (bone softening) in adults.
The vitamin D3-hormone is also often abbreviated as vitamin D. Strictly speaking, this is not a real vitamin, since the body can produce vitamin D hormone itself from precursors in the skin under the influence of UV light. The precursors of vitamin D are derived from cholesterol. Biochemical transformations of vitamin D precursors in the liver and kidneys finally lead to the effective form of vitamin D hormone, 1,25-(OH)2-Cholecalciferol . Man can also absorb this via the digestive tract.