Vitamin D Deficiency and Excess
Vitamin D imbalances can occur in deficiency and excess.
Vitamin D Deficiency is usually caused by low sun exposure, and it manifests with a number of clinical findings.
In particular, decreased calcium and phosphate levels are observed. In addition, increased ALP levels are seen, a surrogate for compensatory bone resorption to restore calcium levels. Likewise, increased PTH levels are also observed, thought to be a compensatory response to hypocalcemia.
In children, vitamin D deficiency leads to a disease known as rickets. It is characterized by rachitic rosary, Harrison's groove, bow legs (genu varus), kyphosis, and fractures. Vitamin D deficiency is also common in infants. In particular, breast milk is a poor source of Vitamin D, and breastfeeding infants without Vitamin D supplementation are at risk for 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 macrophages may express α-1 hydroxylase (usually only in kidney), activating vitamin D to its active form, calcitriol.
Find Vitamin D Deficiency and Excess and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.