Resurrection of vitamin D deficiency and rickets
Michael F. Holick
Michael F. Holick
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Science in Medicine

Resurrection of vitamin D deficiency and rickets

Abstract

The epidemic scourge of rickets in the 19th century was caused by vitamin D deficiency due to inadequate sun exposure and resulted in growth retardation, muscle weakness, skeletal deformities, hypocalcemia, tetany, and seizures. The encouragement of sensible sun exposure and the fortification of milk with vitamin D resulted in almost complete eradication of the disease. Vitamin D (where D represents D2 or D3) is biologically inert and metabolized in the liver to 25-hydroxyvitamin D [25(OH)D], the major circulating form of vitamin D that is used to determine vitamin D status. 25(OH)D is activated in the kidneys to 1,25-dihydroxyvitamin D [1,25(OH)2D], which regulates calcium, phosphorus, and bone metabolism. Vitamin D deficiency has again become an epidemic in children, and rickets has become a global health issue. In addition to vitamin D deficiency, calcium deficiency and acquired and inherited disorders of vitamin D, calcium, and phosphorus metabolism cause rickets. This review summarizes the role of vitamin D in the prevention of rickets and its importance in the overall health and welfare of infants and children.

Authors

Michael F. Holick

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Figure 5

Noncalcemic functions of 1,25(OH)2 D.

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Noncalcemic functions of 1,25(OH)2 ...
Vitamin D coming from the photoproduction of previtamin D or coming from the diet is converted in the liver to 25(OH)D by the vitamin 25-OHase. 25(OH)D is converted in the kidneys by 1-OHase. 1,25(OH)2D not only regulates calcium and phosphorus metabolism but can stimulate the pancreas to produce insulin and to downregulate the renal production of renin. 1,25(OH)2D also interacts with its nuclear receptor (VDR) in a wide variety of tissues and cells and helps maintain normal cell proliferation and differentiation. 25(OH)D can also be converted to 1,25(OH)2D in a wide variety of cells, including colon, prostate, and breast, for the autocrine production of 1,25(OH)2D. It is believed that the autocrine production of 1,25(OH)2D is important for regulating cell growth and maturation, which decreases risk of the cell becoming malignant. 25(OH)D also is metabolized in macrophages by the 1-OHase to produce 1,25(OH)2D. The expression of the VDR and 1-OHase is upregulated when TLR2/1 is stimulated by LPS. This results in an increase in the expression of the VDR and the 1-OHase. The increase production of 1,25(OH)2D increases the nuclear expression of cathelicidin (CD) in the macrophage, which is a cationic peptide that causes the destruction of infective agents including M. tuberculosis.