evidence: D3 is much more toxic than vitamin D2. menadione produces adverse effects; phylloquinone and the menaquinones have negligible toxicities. cThese effects observed after parenteral administration of the vitamin. dNicotinamide is more toxic than nicotinic acid. bOnly 100 PART | I Perspectives on the Vitamins in Nutrition humans, particularly in children. Affected individuals show anorexia, vomiting, headache, drowsiness, diarrhea, and polyuria. There have been no documented cases of hypervitaminosis D due to excessive sunlight exposure. Excessive intakes of vitamin D increase circulating levels of 25-OH-D3, which at high levels appears to bind VDR, thus, bypassing the regulation of the 25-OH-D3-1-hydroxylase to induce transcriptional responses normally signaled only by 1,25-(OH)2-D3. Hypervitaminosis D is characterized by increases in both the enteric absorption and bone resorption of calcium. This produced hypercalcemia and, ultimately, calcinosis, i.e., deposition of calcium and phosphate in soft tissues (heart, kidney, and vascular and respiratory systems). Thus, the risk of hypervitaminosis D depends on concomitant intakes of calcium and phosphorus and is in conditions, such as chronic inflammation, in which the normal feedback regulation of the renal 25-OH-D3-1-hydroxylase is compromised.