Pharmacology Book

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Hypovitaminosis DAka: Vitamin D Deficiency

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  1. See Also
    1. Rickets
  2. Epidemiology
    1. Vitamin D Deficiency is common in U.S.
    2. Incidence increasing due to Sunscreen use and less Time Outdoors
  3. Risk Factors
    1. Elderly
      1. Related to housebound status and decreased Vitamin D absorption
    2. Comorbid illness
    3. Malnourished
    4. Lack of Sun Exposure (or thorough sun screen use)
      1. Those with darker skin require 3-6 fold more exposure
    5. Renal disease (Renal Failure, Nephrotic Syndrome)
    6. Hepatic disease (Cirrhosis)
    7. Gastric surgery (resection or Gastric Bypass)
    8. Small Bowel Resection
    9. Medications
      1. Anticonvulsant use (e.g. Phenobarbital, Phenytoin)
        1. Requires 2-5 fold more Vitamin D intake daily
      2. Corticosteroids (long-term use)
      3. Rifampin
    10. Total Parenteral Nutrition
  4. Pathophysiology
    1. Effects of Vitamin D Deficiency
      1. Altered secretion of Parathyroid Hormone
      2. Altered mineral ion metabolism
        1. Hypocalcemia
        2. Hypophosphatemia
      3. Mineralization defects in skeleton
        1. Osteomalacia in adults
        2. Rickets in children
    2. Step-by-step outcome of Vitamin D Deficiency
      1. Inadequate intestinal calcium absorption
        1. Results in Hypocalcemia
        2. Severe Hypocalcemia occurs in later deficiency
      2. PTH secreted to complensate for Hypocalcemia
        1. Results in secondary Hyperparathyroidism
        2. Calcium mobilized from bone
      3. Increased PTH results in phosphate wasting
        1. Severe hypophophatemia results
  5. Symptoms
    1. Early
      1. Myalgias
    2. Later
      1. Secondary Hyperparathyroidism
        1. Osteoporosis
        2. Osteomalacia
      2. Symptomatic mineral disturbance
        1. See Hypocalcemia
        2. See Hypophosphatemia
  6. Differential diagnosis
    1. See Hypocalcemia
    2. See Hypophosphatemia
    3. See Hyperparathyroidism
    4. Myalgias
      1. See Polymyositis Differential Diagnosis
      2. Consider in those diagnosed with Fibromyalgia
  7. Labs
    1. Serum 25-Hyroxyvitamin D Level
      1. Preferred test (but expensive)
      2. Levels <20 ng/ml suggest deficiency
    2. Ionized Serum Calcium
    3. Serum Phosphorus
  8. Management
    1. Treat Hypocalcemia
      1. Symptomatic Hypocalcemia or Ionized Calcium <3.2 mg/dl
    2. Treat Hypophosphatemia
    3. Vitamin D Replacement
      1. See Vitamin D Replacement
    4. Vitamin D maintenance
      1. Maintain Vitamin D >30-40 ng/ml
      2. See Vitamin D for maintainance doses
  9. References
    1. Holick (2007) N Engl J Med 357(3):266

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