Vitamin D deficiency due to inadequate dietary intake or insufficient sun exposure: This is the most common cause of vitamin D deficiency, as many people do not consume enough vitamin D through their diet or have limited sun exposure, which is necessary for vitamin D production in the skin.

Medication-induced vitamin D deficiency (e.g., anticonvulsants, glucocorticoids): Certain medications can interfere with vitamin D metabolism, leading to deficiency.
Malabsorption syndromes (e.g., celiac disease, Crohn's disease): Conditions that affect the gut can impair vitamin D absorption, contributing to deficiency.
Renal disease: Kidney problems can affect vitamin D activation, leading to deficiency.
Liver disease: Liver conditions can impact vitamin D metabolism, resulting in deficiency.

Hypoparathyroidism: A rare condition where the parathyroid glands are underactive, leading to low calcium levels and potentially vitamin D deficiency.
Pseudohypoparathyroidism: A rare genetic disorder affecting parathyroid hormone response, which can lead to vitamin D deficiency and other metabolic issues.
Rickets or osteomalacia: Conditions characterized by softening of the bones due to severe vitamin D deficiency, which can have serious consequences if left untreated.

Vitamin D-dependent rickets type 1: A rare genetic disorder affecting vitamin D activation in the kidneys.
Vitamin D-dependent rickets type 2: A rare genetic disorder affecting vitamin D receptor function.
Hereditary 1,25-dihydroxyvitamin D-resistant rickets: A rare condition characterized by resistance to the active form of vitamin D.