Aetiology of vitamin D deficiency

Reduced intake of vitamin D:

• lack of sunlight - deficiency of vitamin D3 - cholecalciferol
• dietary lack of vitamin D3 - ergocalciferol
• fat malabsorption - e.g. coeliac disease, pancreatic insufficiency, extrahepatic biliary obstruction

Reduced hepatic production of 25(OH)D3:

• severe chronic liver disease - interference with synthesis of vitamin D binding protein
• induction of hepatic P-450 enzymes accelerating rate of degradation e.g. phenytoin, carbamazepine
• nephrotic syndrome - excess excretion of vitamin D binding protein

Reduced renal production of calcitriol - 1,25(OH)2 D3:

• deficiency of 1 alpha hydroxylase:
  • hereditary - vitamin D dependent rickets type I
  • chronic renal failure
• suppression of 1 alpha hydroxylase action:
  • deficiency of PTH - hypoparathyroidism
  • end organ resistance - pseudohyperparathyroidism

Resistance to calcitriol:

• vitamin D dependent rickets type II

Reference:

1. Kennel KA, Drake MT, Hurley DL. Vitamin D Deficiency in Adults: When to Test and How to Treat. Mayo Clinic Proceedings. 2010;85(8):752-758