Hypervitaminosis D
Excessive intake of vitamin D is toxic. Usually, toxicity . not manifest except after huge doses, which result in calcification of soft tissues due to persistent hypercalcemia. Cases of vitamin D toxicity occur ''because of unjustified and indiscriminate medical use ofthe vitamin, lack of appreciation of its toxicity, and the self-administration of highly concentrated preparations. The maximum safe level of vitamin D for infants has yet to be precisely established, although intakes of 40 mcg (1600 IU )-four times the recommended dietary allowancenave not interfered with the rate of growth in either length weight of infants. However, evidence that certain infants may be more sensitive to the toxic effects of vitamin D and may develop hypercalcemia on intakes of 50 ;ncg (2000 IU) has caused considerable concern regarding the infant's total intake of this vitamin. It is particularly rmportant that the mother recognize the need for vitamin :J, but, even more important, that she be aware of the wmful effects of overdosage. This means, of course, that the physician and the mother should know of the sources of vitamin D in the diet as well as in supplements.
In adults, hypercalcemia has been accompanied by mch symptoms as anorexia, nausea, weight loss, polyuria, mnstipation, and azotemia. Similar symptoms are seen in :m-ants, and, in certain rare severe forms, mental retardation also occurs.
Vitamin D toxicity symptoms are associated with high plasma levels of 25-0H-D3, but normal or even below normal levels of 1,25-(OH)2D3. Because 25-0H-D3 is known to substitute for 1,25-(OH)2D3 at the tissue receptor sites when present in large amounts, it is possible that action in the bone and intestine is responsible for the excessive calcium load brought to the system. Because of the potential danger of high intakes and because there is no known benefit from intake levels above the recom:nended dietary intakes. When a special need for vitamin D therapy is indicated, therapy should be carefully supervised by a physician, and the plasma calcium levels should be monitored continually. Treatment of vitamin D toxicity involves withdrawal of the vitamin supplement, reduction of calcium intake, and administration of a furosemide diuretic. Glucocorticoid therapy may be required to normalize plasma calcium.
