Vitamin D
10
Cholecalciferol (D3)
can be tolerated without harm) is set at 25 micrograms/day (1000 IU). 1000 micrograms/day (40,000 IU) in infants has produced toxicity within 1 month. The U.S. Dietary Reference Intake Tolerable Upper Intake Level (upper limit) of vitamin D for children and adults is set at 50 micrograms/day (2,000 IU). 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, nervousness, pruritus, and ultimately, renal failure. proteinuria, urinary casts, azotemia, and metastatic calcification (especially in the kidneys) may develop. 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. This is because within about 20 minutes of ultraviolet exposure in light skinned individuals (3–6 times longer for pigmented skin) the concentrations of vitamin D precursors produced in the skin reach an equilibrium, and any further vitamin D that is produced is degraded. According to some sources, endogenous production with full body exposure to sunlight is approximately 250 µg (10,000 IU) per day. According to Holick, "the skin has a large capacity to produce cholecalciferol"; his experiments indicate that The similar effect of supplementation and whole body exposure to one erythemal dose prompted a researcher to suggest that 250 micrograms/day (10,000 IU) in healthy adults should be adopted as the tolerable upper limit. Supplements and skin synthesis have a different effect on serum 25(OH)D concentrations; endogenously synthesized vitamin D3 travels in plasma almost exclusively on vitamin D-binding protein (VDBP), providing for a slower hepatic delivery of the vitamin D and the more sustained increase in plasma 25-hydroxycholecalciferol. Orally administered vitamin D produces swift hepatic delivery and increases in plasma 25-hydroxycholecalciferol. The richest food source of vitamin D — wild salmon — would require 35 ounces a day to provide 10,000IU. Recommending supplementation, when those supposedly in need of it are labeled healthy, has proved contentious, and doubt exists concerning long term effects of attaining and maintaining serum 25(OH)D of at least 80nmol/L by supplementation.