Taking too much vitamin D can cause health problems. The condition of having too much vitamin D in the body is known as hypervitaminosis D. The body can produce more than half what it needs with the aid of sunlight. The rest is obtained from the diet. It is highly unlikely for toxicity to occur without the intake of supplements, as the body will not convert more than it needs from the sun, and even fortified foods do not contain excessive amounts of the vitamin.
Function of Vitamin D
The main function of vitamin D is to maintain ideal calcium and phosphorus levels for optimal bone formation. Vitamin D works in the intestines to stimulate absorption and in the kidneys to reabsorb more calcium rather than excrete it. Bone cells turn over constantly, so appropriate mineral levels are necessary on a daily basis throughout the lifespan. Vitamin D also has functions in the immune system, the parathyroid gland and the pancreas.
Intake Levels
The Adequate Intake, established by the Food and Nutrition Board, ranges from 200 to 400 International Units (I.U.) per day based on age up to 70 years. Tolerable Upper Limits established by the Food and Nutrition Board are 1,000 I.U. per day for infants and 2,000 I.U. for children and adults. According to the Merck Manual, intake of 40,000 I.U. per day in infants and 50,000 I.U. in adults will cause toxicity after one month or more.
Toxicity Symptoms
Toxicity of Vitamin D leads to elevated levels of calcium in the blood. Symptoms include nausea, vomiting, poor appetite, constipation, fatigue and irritability. High blood calcium levels also can cause heart rhythm abnormalities. Kidney stones also may occur. In extreme cases, calcium deposits may form in soft tissues such as the kidneys and may even progress to kidney failure.
Toxicity Diagnosis
According to the Medline encyclopedia from the National Institutes of Health, diagnostic tests for hypervitaminosis D include blood tests for elevated calcium, phosphorus and vitamin D levels, urine tests for high calcium levels and X-rays of the bones. According to the Merck Manual, calcium blood levels should be monitored regularly in all patients receiving high-dose supplements of vitamin D to prevent toxicity from occurring.
Toxicity Treatment
After stopping all vitamin D supplements, steps may be needed to reduce calcium levels. Proper hydration may require intravenous administration of fluids. Corticosteroids may be given to further reduce calcium levels. Hospitalization may be required to treat vitamin D toxicity.
Prognosis
Recovery from vitamin D toxicity is expected unless deposits of calcium have formed in the soft tissues. Kidney damage or other calcifications may be irreversible.
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