Vitamin D toxicity is rare, but it can occur if you take too much supplemental vitamin D. The initial signs of toxicity may be mild, but an overdose of vitamin D can eventually damage organs. The levels of vitamin D required to produce an overdose are atypical and toxicity requires taking vitamin D over the course of months, not all in one dose.
Biology
The signs of vitamin D toxicity don't come directly from the action of vitamin D itself, but from hypercalcemia, high levels of calcium caused by an overdose of vitamin D. This occurs because vitamin D regulates the balance of calcium and phosphorus in the body. In hypercalcemia, calcium levels rise in the blood to between 12 and 16 mg/ dL. A high level of calcium in the blood along with high serum levels of vitamin D or a history of high vitamin D intake can indicate hypercalcemia caused by vitamin D toxicity.
Symptoms
Nausea, vomiting and anorexia are the first symptoms of vitamin D toxicity to develop. Weakness, nervousness, protein in the urine and renal failure may follow. When left untreated for long periods of time, high levels of vitamin D can lead to kidney stones, bone loss and calcification of the kidneys, heart or other organs.
Amounts
Hypercalcemia generally requires extremely high vitamin D doses, of 50,000 IU a day or more, to develop. According to Merck Manuals, toxicity can be observed in infants taking 40,000 IU or more daily after one to four months of use and in adults taking 50,000 IU daily after several months. The current recommendation of an upper limit of 2,000 IU daily is extremely conservative, as hypercalcemia has not been established for doses under 10,000 IU in normal, healthy adults. Vitamin D toxicity from sun exposure has never been observed, according to the Linus Pauling Institute at Oregon State University.
Response
When someone exhibits signs of vitamin D toxicity, they will be tested for the presence of high levels of vitamin D and calcium. If hypercalcemia is confirmed, saline and corticosteroids can be administered via IV along with a high level of fluids to flush the system of excess calcium. Vitamin D supplementation should be halted immediately upon noticing any signs of toxicity.
Considerations
Some people are more prone to developing vitamin D toxicity. People with hyperparathyroidism, sarcoidosis, tuberculosis and lymphoma may notice signs of toxicity at lower doses than other individuals. Anyone at risk for vitamin D toxicity, including people who are taking high doses of this vitamin, should have their blood serum regularly monitored for both vitamin D and calcium levels to avoid hypercalcemia.
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