Common causes of vitamin D deficiency are inadequate vitamin D skin production, less dietary vitamin D intake and impaired absorption. Other causes of vitamin D deficiency include vitamin D loss, abnormal metabolism, resistance to vitamin D and medication.^[1]

Vitamin D deficiency may be caused by:^{[1][2][3][4][5][6][7][8]}

• Inadequate vitamin D skin production
• Inadequate vitamin D dietary intake
• Vitamin D loss
• Malabsorption
• Impaired metabolism
• Resistance to Vitamin D
• Medication

• Antiepileptic medication
• Glucocorticoid
• Inadequate sun exposure including dark skin and clothing
• Inadequate vitamin D dietary intake
• Malabsorption

• Autosomal dominant hypophosphatemic rickets
• Celiac disease
• Chronic kidney disease: impaired renal 1α-hydroxylation
• Crohn disease
• Cystic fibrosis
• Highly active antiretroviral therapy (HAART)
• Hyperthyroidism
• Impaired enterohepatic circulation
• Nephrotic syndrome
• Post gastric bypass surgery
• Primary hyperparathyroidism
• Rifampin
• Sarcoidosis
• Severe liver failure: impaired hepatic 25-hydroxylation
• Short bowel syndrome
• St John’s wort
• Tuberculosis
• Type I hereditary vitamin D–dependent rickets
• Type II hereditary vitamin D–dependent rickets
• Vitamin D-resistant rickets
• Whipple disease
• X-linked familial hypophosphatemia

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