Table 1.

Examples of some causes of vitamin D deficiency or resistance.

Causes of vitamin D deficiency or resistance
Deficient intake or absorption	➢Dietary ➢Inadequate sunlight exposure ➢Malabsorption ➢Gastrectomy ➢Small bowel disease ➢Pancreatic insufficiency
Defective 25-hydroxylation	➢Liver disease/failure ➢Alcoholic cirrhosis ➢Anticonvulsants
Loss of vitamin D binding protein	➢Nephrotic syndrome
Defective 1-alpha 25-hydroxylation	➢Hypoparathyroidism ➢Chronic kidney disease/failure ➢1-alpha hydroxylase deficiency (Vitamin D-dependent rickets type 1)
Defective target organ response to calcitriol	➢Hereditary vitamin D-resistant rickets (Vitamin D-dependent rickets, type 2)