Vitamin D
Vitamin
Overview
- Vitamin D is a fat-soluble secosteroid hormone primarily existing as vitamin D₃ (cholecalciferol) and vitamin D₂ (ergocalciferol).
- It's synthesized in the skin after ultraviolet-B (UV-B) exposure or obtained from diet and supplements.
- Its main role is maintaining calcium and phosphorus homeostasis, supporting bone mineralization and skeletal health.
Chemistry
- Vitamin D₃ (cholecalciferol) has the molecular formula C₂₇H₄₄O, molar mass 384.64 g·mol⁻¹.
- Its IUPAC name is (3S,5Z,7E)-9,10-secocholesta-5,7,10-trien-3-ol.
- Vitamin D₂ (ergocalciferol) is C₂₈H₄₄O, differing by a double bond in the side chain (C22–C23).
- Both are secosteroids, derived from a sterol scaffold where the B-ring is broken (“seco”), producing a triene system (C5–C7–C10) and a hydroxyl group at C3 essential for VDR binding.
- They are lipophilic (log P ≈ 6–7), require fat for intestinal absorption, and are stable to heat but degrade under UV-C, requiring opaque, airtight packaging.
Sources & Quality
- Natural vitamin D is produced in human skin from 7-dehydrocholesterol upon UV-B exposure.
- Dietary sources include fatty fish (salmon, mackerel), cod liver oil, egg yolk, and fortified foods (milk, cereal).
- Commercially, vitamin D₃ is most commonly extracted from lanolin (sheep wool) or produced via synthetic pathways from 7-dehydrocholesterol derived from plant sterols.
- Vitamin D₂ is produced by UV-irradiating ergosterol from yeast or fungi.
- High-quality supplements use pharmaceutical-grade cholecalciferol with ≥ 98% purity, verified by HPLC.
- Quality considerations include: absence of heavy-metal contaminants, validated potency (± 5% of label), and stability (protected from light and oxygen).
- Third-party testing (e.g., USP, NSF) ensures compliance with label claims and safety standards.
Where to Buy Vitamin D
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