Vitamin D

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Bottom line: 200IU/day in 50-64y.o. 400-800IU/day in ≥65y.o. or with osteoporosis

Basics

  • Precursor in cholesterol synthesis
  • Exists principally in 2 forms:
    1. Ergocalciferol (D2)
    2. Cholecalciferol (D3)

Dietary Sources

  • The sun
  • Fish oils
  • Egg yolk

Metabolism

  • Vitamin D —(skin)→ Vitamin D3 —(liver)→ 25-hydroxy vitamin D3 —(kidney)→ 1,25-dihydroxy vitamin D3
  • 7-dehydrocholesterol → cholecalciferol → 25-hydorxycholecalciferol → 1,25-dihydorxycholecalciferol

Target Organs

  • As a hormone:
    • mineral metabolism
    • bone growth
      • stimulates differentiation of osteoclasts
    • stimulates intestinal absorption of calcium
    • also phosphate and magnesium ions
  • binds to intracellular receptors that function as transcription factors to modulate gene expression.
  • stimulates expression in calcium-transporting proteins like calbindin
  • Vitamin D receptors are present in most (if not all) cells in the body


Deficiency

  • classic manifestation is rickets (children)
  • also osteomalacia in adults
  • can be genetic etiology
  • can be due to liver or kidney problems
  • can be due to insufficient exposure to sunlight

Toxicity

  • Almost always the result of Vitamin D supplement overdose
  • can't be caused by overexposure to the sun
  • Simply a toxicity issue

Daily intake

  • According to Osteoporosis society of Canada, 200IU/day in 50-64y.o. 400-800IU/day in ≥65y.o. or with osteoporosis
  • Calcium!!

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