The Biological Activities of Vitamin D and Its Receptor in Relation to Calcium and Bone Homeostasis, Cancer, Immune and Cardiovascular Systems, Skin Biology, and Oral Health

Table 1

Causes of Vitamin D deficiency or functional impairment.

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(i) Decreased exposure to sunlight

(ii) Impaired photosynthesis in the skin

(iii) Inadequate diet

(iv) Impaired intestinal absorption

(v) Impaired conversion of Vitamin D into active metabolites owing to liver or renal disease

(vi) Resistance to the biological effects of 1,25 (OH)₂D

(vii) Accelerated inactivation of vitamin D metabolites (barbiturates, phenytoin, and rifampin)

(viii) Medications (anticonvulsants, systemic glucocorticoids, ketoconazole, or antiretrovirals)

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