Vitamin D Deficiency and Excess
Vitamin D deficiency is usually caused by low sun exposure, and it manifests with a number of clinical findings. Since vitamin D is responsible for calcium and phosphate absorption in the GI tract, it leads to a decrease in these lab values. Moreover, it leads to increased ALP levels, which increases bone resorption to compensate. Similarly, PTH levels also increase in an attempt to elevate calcium levels. In children, vitamin D deficiency leads to a disease known as rickets. It is characterized by rachitic rosary, harrison's groove, bow legs, kyphosis, and fractures. Vitamin D deficiency is also common in infants. In particular, breastfeeding with supplementation is a common cause of deficiency. In addition to deficiency, vitamin D excess can also lead to a number of problems. It is characterized by hypercalcemia, loss of appetite, and stupor. It is commonly caused by granulomatous diseases, as epithelioid macrophase may express α-1 hydroxylase which activates vitamin D.