Functions

Vitamin D (calciferol D1; ergocalciferol D2; cholecalciferol D3) is a prohormone for normal growth and development, normal bones and teeth, absorption and metabolism of calcium, phosphorus and magnesium. Prevents osteoporosis and osteomalacia.

The precursor to Vitamin D is made in the liver. This precursor migrates to the skin and is converted to a second precursor with the help of ultraviolet rays. The liver and kidney convert this second precursor to active vitamin. Alternatively, Vitamin D may be obtained from food sources.

Vitamin D works with parathyroid hormone to regulate calcium levels in the blood, along with promoting normal bone mineralization. Vitamin D also supports basic cell processes in the brain and kidney, liver, skin, reproductive organs, and immune system.

Uses

May be used therapeutically in osteoporosis; kidney-related bone problems; hypoparathyroidism (calcium & phosphorus absorption, resorption, mineralization, & collagen maturation of bone). May also be useful in osteo and rheumatoid arthritis.

Deficiency

A deficiency of Vitamin D interferes with calcium and phosphorus use in bone and teeth formation, therefore in a deficiency bone may fail to calcify; may be implicated in irritability; weakness; osteomalacia; rickets,tetany or muscle spasm and pain. Repeated pregnancies and periods of lactation may deplete it, as may insufficient exposure to sunlight.

Antagonists

Production of vitamin D is blocked by anything which blocks ultraviolet including skin pigment, smog, fog, sunscreen, windows and hats.

Co-factors

Sunlight converts 7-dehydrocholesterol to cholecalciferol. Fat in the intestine is required for absorption of vitamin D. Pantothenic acid is necessary for the synthesis of vitamin D.

Drug Interactions

The cholesterol-lowering drug, cholestyramine, and mineral oil laxatives interfere with the absorption of vitamin D. Alcohol interferes with the conversion of vitamin D to its biologically active form. People taking certain anticonvulsant drugs, such as phenytoin, may decrease the activity of vitamin D by increasing its metabolism. People taking this drug are likely to be at increased risk of osteoporosis and have high vitamin D requirements.

Dose

RDA: 200 IU/d adults, 400IU if over 50, 600IU if over 70; 400-600 pregnant & lactating women; 400 infants

Toxicity

Vitamin D is the most toxic of all the vitamins, since it is sotred in adipose tissue and is released slowly. It is contraindicated in heart disease. Excess Vitamin D may cause hypercalcemia; anorexia; weight loss; n&v; diarrhea; constipation; confusion; irritability; depression;stupor; polyuria; renal failure and kidney stones; polydipsia, bone pain and weakness, calcium deposits in tissue. Tolerable upper intake limit has been set at 2000IU.

Sources

Vitamin D is found in:

Fish liver oils

Fish-salmon, herring, tuna, sardines

Egg yolk

Butter

Light-sprouted seeds (UV light)

Milk when it is supplemented