Vitamin D overdose causes hypercalcemia, and the main symptoms of vitamin D overdose are those of hypercalcemia:
anorexia, nausea, and vomiting can occur, frequently followed by
polyuria,
polydipsia, weakness, insomnia, nervousness,
pruritus, and, ultimately,
renal failure.
Proteinuria,
urinary casts,
azotemia, and
metastatic calcification (especially in the kidneys) may develop.
[87] Other symptoms of vitamin D toxicity include... abnormal bone growth and formation, diarrhea, irritability, weight loss, and severe depression.
[49][73] Vitamin D toxicity is treated by discontinuing vitamin D supplementation and restricting calcium intake. Kidney damage may be irreversible.
Exposure to sunlight for extended periods of time does not normally cause vitamin D toxicity.
[88] Within about 20 minutes of ultraviolet exposure in light-skinned individuals (three to six times longer for pigmented skin), the concentrations of vitamin D precursors produced in the skin reach an
equilibrium, and any further vitamin D produced is degraded.
[91]
Published cases of toxicity involving hypercalcemia in which the vitamin D dose and the 25-hydroxy-vitamin D levels are known all involve an intake of ≥40,000 IU (1,000 μg) per day.
[8