Vitamin D excess

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 hypercalcemia due to increased bone resorption (1).

• Early symptoms of toxicity include symptoms of hypercalcemia 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  • if vitamin D toxicity secondary to excessive supplementation is suspected then vitamin D must be withdrawn and serum calcium and renal function checked urgently, since emergency inpatient care with rehydration is usually indicated (1).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:

• the Food Standards Agency states that taking 25 mcg (1,000 IU) of vitamin D supplements daily is unlikely to cause any harm in the general population (1,2)
  • up to 250 mcg (10,000 IU) can be taken daily for healthy people for up to 16 weeks without toxicity (1)
• pregnancy (2)
  • 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 (10 mcg [400 IU] daily) seems reasonable

Reference:

• (1) Primary vitamin D deficiency in adults Drug and Therapeutics Bulletin 2006;44:25-29.
• (2) Primary vitamin D deficiency in children Drug and Therapeutics Bulletin 2006;44:12-16.