Vitamin D, like all vitamins, is needed in relatively small amounts for your body to function properly. You can get vitamin D from your diet, but it is also synthesized by your body in response to sunlight. If you consume too much vitamin D, you can develop vitamin D toxicity, which causes elevated levels of calcium in your blood.
Vitamin D Function
Vitamin D is important because it is needed for your digestive tract to absorb calcium from your diet. Vitamin D on its own is not active, but it gets converted by the liver and the kidneys to form the active form of vitamin D, also known as calcitriol, the Merck Manual explains. Calcitriol then stimulates the uptake of calcium by your intestines. If you consume too much vitamin D, your blood levels of calcium will rise.
Symptoms
The symptoms of a vitamin D overdose are generally caused by the elevated calcium levels. High levels of calcium can affect the digestive tract and cause nausea, constipation and vomiting. The heart is sensitive to calcium levels and having too much calcium in your blood can result in an irregular heartbeat, the Mayo Clinic states. Vitamin D toxicity can also cause confusion and muscle weakness. Over time, ingestion of too much vitamin D can also increase your risk of developing kidney stones.
Causes
The synthesis of the active forms of vitamin D are carefully regulated by the body, the Merck Manual notes, so most cases of vitamin D toxicity are caused by consuming abnormally large amounts of vitamin D supplements or multivitamins. Doses of 1,000 mcg per day can cause toxicity in infants and a dose of 1,250 mcg per day over the course of several months can cause toxicity in adults. Vitamin D toxicity can also occur due to overtreatment of hypoparathyroidism.
Considerations
According to the Vitamin D Council, the risks of vitamin D toxicity are overstated. The vitamin D council states that one vitamin D supplement, cholecalciferol, is generally not toxic unless extremely high amounts are taken. The Vitamin D Council also notes that some cases of vitamin D toxicity are actually caused by hypersensitivity to vitamin D. This can be due to an overactive hyperthyroid gland or by kidney abnormalities which result in the synthesis of too much of the active form of vitamin D.
