Vitamin D is an important vitamin for various organs in the body. It is called a prohormone, which means that it is a precursor to active hormones. The main function of vitamin D is to increase absorption of calcium and phosphate from the intestine. Overdose of vitamin D can cause hypercalcemia, or high calcium levels.
The facts about vitamin D
Vitamin D has two forms, vitamin D2 and D3. According to the Merck Manual, vitamin D3 is the naturally occurring form of the vitamin, synthesized in the skin as a result of exposure to ultraviolet radiation from the sun. Vitamin D is also added to fortified milk and other foods. The liver and the kidneys convert vitamin D to calcitriol, its active form. Because this process is tightly regulated, vitamin D toxicity results from excessive ingestion of the vitamin in supplements.
Symptoms and Complications
Symptoms of vitamin D toxicity are a result of the increased calcium level. Initial symptoms include nausea, vomiting and loss of appetite. Other symptoms include polyuria, or frequent urination; polydipsia, or excessive thirst; nervousness and weakness. Renal, or kidney, damage results after continuing exposure to toxic vitamin D levels. Proteinuria, or the presence of excessive protein in the urine, results from kidney damage. This makes the urine appear frothy. Vitamin D toxicity also causes azotemia, a condition in which the kidneys become unable to filter out of the body the waste products of cellular metabolism. This causes accumulation of nitrogen-containing products, like urea, in the blood stream.
Diagnosis
When a person presents with the symptoms of vitamin D toxicity, several tests are necessary to make the diagnosis. Calcium levels usually become high, and further tests will prove necessary to determine if this results from vitamin D toxicity or other causes. According to Lab Tests Online, the best test to determine levels of vitamin D is the total 25-hydroxyvitamin D level. Disorders of the parathyroid glands also need to be ruled out, as this gland also helps control the levels of calcium in the body.
Treatment
The first intervention to treat vitamin D toxicity is decreasing or stopping the intake of vitamin D supplements. Other treatments include intravenous fluids to increase hydration and flush the kidneys of excess calcium and medicines, like corticosteroids and biphosphonates, that decrease blood calcium levels. Nutritional counseling will help to prevent a recurrence of the symptoms and to prevent ingestion of toxic levels of vitamin D and other vitamin supplements.
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