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VITAMIN DDr SIVARAJ SDEPT OF PHYSIOLOGYALL INDIA INSTITUTE OF MEDICAL SCIENCESNEW DELHI
Known as the “Sunshine vitamin” Can be produced in the body, has specific target tissues Dietary requirement is not essential
Sources sources of vitamin Major source synthesis in the D3, providing only 0.4 to 1 skin ultraviolet B (wavelength mcg/L. 290–315 nm) Vitamin D3 exists naturally in animal products, and the richest sources are fish liver oils Except for fish, food (unless fortified) contains only limited amounts of vitamin D Vitamin D2 (ergocalciferol) is obtained from plant sources and is the chemical form found in some supplements. Human milk and unfortified cows milk tend to be poor
Absorption, Transport and Storage Vit D+other lipids Micelles Incorporated into chylomicrons Plasma Chylomicron remnants or DBP Liver peripheral tissue
Functions Maintenance of calcium and phosphorus homeostasis Gene expression In the bone PTH alone or with calcitriol, estrogen, or both, moves calcium and phosphorus from the bone to maintain normal blood levels In the kidney calcitriol increases renal tubular reabsorption of calcium and phosphate.These activities are coordinated with the purpose of maintaining plasma calcium concentrations within a narrow range.
RDA The AI increases to 10 mcg/day(400IU) for adults age 5l years and older and increases even more to 15 mcg/day( 600IU) for adults 71 years and older The UL for vitamin D for infants is 25 mcg/day (1000 IU) and for children and adults,50mcg/day (2000 IU)
Deficiency Risk factors• Old age• Lack of sun exposure,• Dark skin• Fat malabsorption• Obesity Rickets Osteomalacia In children in adults
Rickets Impaired mineralization of growing bones Involves Ca Phosphorus and Vitamin D Clinical features• Bone pain, muscular tenderness, and hypocalcemic tetany• Bowed legs, “knock knees," beaded ribs (the rachitic rosary), pigeon breast, and frontal bossing of the skull Radiology• Enlarged epiphyseal growth plates Treatment Rickets caused strictly by vitamin D deprivation can be treated effectively with oral preparations of the vitamin or natural sources rich in the vitamin
Osteomalacia Involves generalized reductions in bone density and the presence of pseudofractures, especially of the spine, femur, and humerus Clinical features• Muscular weakness and bone tenderness• Greater risk of fractures, particularly of the wrist and pelvis Prevention Possible with adequate consumption of vitamin D
Toxicity• Infants and small children are most susceptible to hypervitaminosis D• The UL for vitamin D is 25 mcg (1000 IU)/day for infants and 50 mcg (2000 IU)/day for children and adults.