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vitamin D excess

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Excessive vitamin D may be the result of:

  • excessive intake:
    • self-medication, for example in women concerned about osteoporosis, supplementation during pregnancy (see notes)
    • iatrogenic
  • increased production of calcitriol:
    • high 1-alpha-hydroxylase in kidney, for example in hyperparathyroidism
    • extra-renal production of calcitriol - 1-alpha-hydroxylase activity in granuloma cells, for example in sarcoidosis, sarcomas, some lymphomas

The features of vitamin D excess are those of hypercalcaemia due to increased bone resorption

  • early symptoms of toxicity include symptoms of hypercalcaemia such as thirst, polyuria and constipation
    • vitamin D toxicity can result in renal failure, which can rapidly become irreversible
    • if vitamin D toxicity secondary to excessive supplementation is suspected then vitamin D must be withdrawn and serum calcium and renal function checked urgently, since emergency inpatient care with rehydration is usually indicated (1)

Notes (2):

  • the Food Standards Agency states that taking 25µg (1,000 IU) of vitamin D supplements daily is unlikely to cause any harm in the general population
  • pregnancy
    • excess vitamin D in animals has been shown to have teratogenic effects. High systemic doses of vitamin D should be avoided during pregnancy
      • in consideration of all these factors in mind, the currently recommended dose for supplementation during pregnancy and breast-feeding (10µg [400 IU] daily) seems reasonable

Reference:

  1. Drug and Therapeutics Bulletin 2006;44 (4):25-9.
  2. Drug and Therapeutics Bulletin 2006; 44(2):12-16.

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