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Vitamin D Deficiency 1

Vitamin D deficiency


Vignette: A 28-year-old woman with a history of chronic kidney disease presents to her physician with severe fatigue and weakness. She also reports experiencing muscle cramps, constipation, and depression. Her serum calcium level is found to be 9.0 mg/dL (normal: 8.5-10.2 mg/dL) and her serum phosphate level is 14.0 mg/dL (normal: 2.5-4.5 mg/dL). Her physician suspects secondary hyperparathyroidism. This is most likely due to a deficiency in which of the following vitamins?


A. Vitamin A

B. Vitamin B12

C. Vitamin C

D. Vitamin D

E. Vitamin E


D. Vitamin D


Secondary hyperparathyroidism is a common complication of chronic kidney disease. The kidneys are responsible for the final step in the conversion of vitamin D to its active form, calcitriol. Calcitriol promotes calcium absorption from the gut and reabsorption from the kidneys, thereby increasing serum calcium levels. It also inhibits PTH secretion. In chronic kidney disease, the kidneys' ability to convert vitamin D to calcitriol is impaired. This leads to decreased serum calcium levels, increased serum phosphate levels (due to decreased phosphate excretion), and increased PTH secretion as the body tries to compensate for the low calcium levels. Increased PTH secretion leads to secondary hyperparathyroidism.


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