Hypervitaminosis D
Vitamin D toxicity brings about increased absorption of Ca and P from the intestine and thus increased blood levels of these minerals. Calsification of a variety of tissues in different species has been observed. Gillman and Gilbert reported arterial lesions and kidney injury in rats. Calcification of the vascular system was prominent in D3 toxicity in calves. In dogs toxic symptoms included a reduction of glomerular filtration and renal flow which may be secondary to renal calcification.
Obviously, human toxicity has not been studied experimentally, although Jeans and steams showed growth retardation in infants on elevated intakes. According to Kramer et. al., the tolerable dose in humans is highly variable. These workers reported that in one instance 400 IV daily (recommended intake) was fatal. They also indicated that general calcinosis in humans takes at least 14 days and is a reversible process if the dose of vitamin D was not too high. The simultaneous intake of a large amount of vitamin A markedly reduces the to~c-effects due to excessive vitamin D intake.
