Vitamin D deficiency is a condition wherein there is low circulating levels of vitamin D. Vitamin D is an essential steroid hormone found in the body.

It results from inadequate sunlight exposure, malabsorptions &/or inadequate nutrition.

Vitamin D insufficiency is a less severe state of calcidiol deficiency and associated w/ parathyroid hormones and osteoporosis.



Vitamin D

  • Fat-soluble vitamin which acts as a hormone and steroid
  • A prohormone synthesized in the skin after ultraviolet radiation exposure or absorbed from food sources
  • Provides adequate levels of calcium and phosphorus via increased intestinal absorption
  • Normal values: 20-100 ng/mL (50-250 nmol/L)
  • Forms of vitamin D:
    • Ergocalciferol (Vitamin D2)
      • Found in some plant foods and most vitamin D supplements
      • Formed upon exposure of ergosterol to irradiation
    • Cholecalciferol (Vitamin D3)
      • Produced in sunlight exposed skin
      • Found in animal products
      • Formed when ultraviolet-B (UV-B) radiation converts 7-dehydrocholesterol in epidermal keratinocytes and dermal fibroblasts to pre-vitamin D which isomerizes to vitamin D3
    • Calcidiol (25-hydroxyvitamin D or 25[OH]D)
      • Storage form of vitamin D
      • Formed in the liver after vitamin D bound to vitamin-D-binding protein (DBP)
      • Transported to the liver to undergo 25-hydroxylation to 25(OH)D
      • Major circulating form of vitamin D
      • Preferred monitoring indicator for vitamin D status due to its long circulating half-life of 2-3 weeks
    • Calcitriol (1,25-hydroxyvitamin D or 1,25[OH]2D)
      • Active form of vitamin D
      • Formed in the kidney after 25(OH)D undergoes 1α-hydroxylation to form 1,25(OH)2 vitamin D
      • Circulating half-life: Approximately 4 hours
      • Regulated by calcium, PTH and phosphate serum levels
      • Used in cases of acquired and inherited metabolic disorders of 25(OH)D and phosphate including chronic kidney disease, chronic granuloma-forming disorders, hereditary phosphate-losing disorders, oncogenic osteomalacia, pseudovitamin D-deficiency rickets and vitamin D-resistant rickets
      • Appears normal or elevated in cases of vitamin D deficiency due to secondary hyperparathyroidism
  • Sources:
    • Skin exposure to sunlight
      • May require at least 3-5x longer exposure to make the same amount of vitamin D with naturally dark skin toned people
    • Food sources: Eggs, meat, mushrooms, oily fish (eg mackerel, salmon, sardines), cod liver oil and other fish oils
    • Fortified food sources: Milk, bread products, orange juices, cereals, yogurts and cheeses
  • Suggested dietary intakes of vitamin D
    • Infants and children aged 0-1 year old: At least 400 IU/day; at least 1000 IU/day to maintain blood levels >30 ng/mL (75 nmol/L)
    • Children >1-18 year old and adults ≤70: At least 600 IU/day; at least 1500-2000 IU/day to maintain blood levels >30 ng/mL (75 nmol/L)
    • Adults aged >70 years old: At least 800 IU/day; at least 1500-2000 IU/day to maintain blood levels >30 ng/mL (75nmol/L)
    • Pregnancy and lactating women: At least 600 IU/day; at least 1500-2000 IU/day to maintain blood levels >30 ng/mL (75nmol/L)
    • Obese children and adults, children and adults on anticonvulsant medications, antifungals (eg Ketoconazole), antiretrovirals, and glucocorticoids: At least 2-3 times more than doses for their age group to achieve body’s vitamin D requirements
  • Major functions:
    • Increases intestinal absorption of calcium and phosphorus
    • Prompts osteoclast maturation to resorb calcium from bones

Non-Pharmacological Therapy

Sunlight exposure

  • Mild sunburn is equivalent to 10,000 to 25,000 IU dietary vitamin D
  • Infants <6 months should be kept out of direct sunlight
  • Full-body exposure in summer months for light pigmented skinned adults should be for 10-15 minutes to generate between 10,000-20,000 IU vitamin D3 within 24 hours
  • For individuals with darker pigmented skin 5-10 times more exposure will generate 10,000-20,000 IU vitamin D3


  • Rich in vitamin D sources (eg cod, mackerel and salmon)
  • Fortified food products (eg diary products, orange juices)
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