Table 1. Main clinical conditions associated with vitamin D deficiency.
| Insufficient production: cutaneous, hepatic, or renal | Increased metabolization/consumption | Reduced intestinal absorption |
|---|---|---|
| Older age | Medications: anticonvulsant agents (phenobarbital, carbamazepine, diphenylhydantoin), ketoconazole isoniazid antiretrovirals (efavirenz, tenofovir) antibiotics | Intestinal malabsorption: inflammatory diseases, celiac disease, Crohn’s disease, cystic fibrosis, pancreatic insufficiency |
| Dark skin | Inflammatory conditions (SLE, RA, tuberculosis) | Bariatric surgery, pancreatic or intestinal resections |
| Physical barriers (sunscreen, clothing, glass) | Primary hyperparathyroidism | Medications: orlistat, cholestyramine |
| Obesity | Osteoporosis treatment with teriparatide or PTH (1-84) | |
| Reduced solar exposure (pregnancy, risk of skin cancer, post-transplantation, SLE) | ||
| Reduced 25(OH)D production: severe hepatic impairment | ||
| Reduced 1,25(OH)2D production/action: chronic kidney disease and vitamin D-dependent rickets type I and II, X-linked hypophosphatemic rickets, and other conditions associated with excessive FGF-23 |
SLE: systemic lupus erythematosus; RA: rheumatoid arthritis; 25(OH)D: 25-hydroxyvitamin D; 1,25(OH)2D: 1,25 dihydroxyvitamin D; FGF-23: fibroblast growth factor 23.