This typically occurs when the 1,25 dihydroxyvitamin D3 levels in the blood are low and there is hypocalcemia. A lack of 1,25 dihydroxyvitamin D3 can result from a deficient dietary intake of vitamin D, or from a lack of exposure of the skin to sunlight, so the body cannot make its own vitamin D from cholesterol.[11] The resulting hypovitaminosis D is usually due to a partial combination of both factors. Vitamin D3 (or cholecalciferol) is converted to 25-hydroxyvitamin D (or calcidiol) by the liver, from where it is transported via the circulation to the kidneys where it is converted into the active hormone, 1,25 dihydroxyvitamin D3.[6][11] Thus a third cause of secondary hyperparathyroidism is chronic kidney disease.