VITAMIN D (D-3: Cholecalciferol; D-2: Ergocalciferol)

General - oil-soluble; rickets-preventive factor; sunshine vitamin; bone & tooth itamin;

• D-3 (natural form) found in fish liver oils or produced by UV (sun) irradiation of 7-dehydrocholesterol (derivative of cholesterol obtained from lanolin) in the fatty layers of the skin; Vitamin D3 has recently been found to be up to 9 times more biologically active than the D2 form.
• D-2 (vegetarian form) produced by UV irradiation of ergosterol, a compound derived from yeast;
• History: oil-soluble anti-rickets factor suggested in 1918; anti-rickets factor found present in cod liver oil (used since early 1800’s) in 1920; crystallized in 1930; identified in 1937;

Nutrition

• Sources: fish livers, beef liver, egg yolks; sunshine on skin; milk (fortified with D);
• Supplements: A + D, multi-vitamin, multi-mineral-vitamin formulations;
• Absorption: upper part of small intestine; along with dietary fats; 80% of intake absorbed; skinformed vitamin D absorbed into lymphatics; alpha-globulin 2 carries it in blood;
• Improved by: edible fats & oils; taking with meal;
• Synergists: Vitamins A & C prevent vitamin D oxidation; vitamins B-1 & B-3 increase tolerance for vitamin D; calcium controls bone formation;
• Antagonized by: cortisone, some anti-convulsants;
• Stability: destroyed by oxygen & light;
• Storage: mainly in liver; also in skin, spleen, bones;
• Excretion: in bile;
• Metabolism: D-3 & D-2 converted to calcidiol in liver; calcidiol converted to calcitriol (active form) in kidneys;
• Interactions: sedatives, tranquilizers, anti-convulsants turn vitamin D to inactive forms;

Functions of vitamin D

• Functions as hormone; stimulates synthesis of calcium & phosphorus binding proteins, that increase absorption of these elements; regulates absorption & metabolism of calcium & phosphorus; acts in conjunction with parathyroid hormone to stimulate release of calcium from bone into blood; stimulates re-absorption of calcium & phosphorus from kidneys;
• Especially important in infancy & childhood for bone development;
• Co-enzyme in metabolic processes in bone, kidney, liver & intestine;
• Regulates growth, hardening & repair of bone;
• Regulates eruption, growth & hardness of teeth;
• Helps synthesize mucosal enzymes used in active transport of calcium;
• Maintains stable nervous system & heart action;
• Functions antagonized by: sedatives, tranquilizers, anti-convulsants;

Quantities

• Measurement: μg and IU; 10 μg cholecalciferol = 400 IU of Vitamin D;
• Optimum: (SONA) average ranges from 10 to 24 μg /day (10 μg = 400 IU);
• Minimum: (DRI) average set at 5/15 μg (400/600 I.U.) /day;
• Less than RDA: % unknown; especially common in elderly & others living indoors;
• Deficiency of vitamin D results from lack of skin exposure to sunshine; lack in diet; poor intestinal absorption (bowel disease); mineral oil;
• If early in life: symptoms include rickets: permanent skeletal malformation (bowed legs, concave breast, beaded ribs, large head, late eruption of teeth); retarded growth; soft, decay-sensitive teeth; nervous irritability;
• In adults: adult rickets (osteomalacia): symptoms can manifest as bone demineralization & softening; reduced parathyroid activity; lack of vigour; diminished kidney function; muscular weakness; osteoporosis;
• Toxicity is unusual (requires about 3,000 IU/day in infants and 1,000 IU/day/pound of body weight in adults);
• Toxic levels of D-2 (ergocalciferol) may increase blood calcium levels (hypercalcaemia), that cause appetite loss, nausea, weight loss & failure to thrive; affects all tissues adversely; encourage development of atherosclerosis; bind magnesium; cause calcium deposits in soft tissues & inner organs (calciphylaxis);
• Block toxic reaction with large doses of vitamin E, C & choline;

Therapy with vitamin D

• Usual therapeutic range is 400 - 1,000 IU/day;
• Allergic conjunctivitis - high doses (50,000 IU/day) removed symptoms in those tested;
• Rectifies chronic calcium deficiency; helps in chronic asthma, arthritis & depression;
• Somewhat effective in treating menopausal symptoms, including irritability, depression, hot flashes, leg cramps & night sweats;
• Offsets toxic effects of lead & other heavy metals if used with pharmacological agents;
• Reduces the incidence & severity of common colds when used together with vitamin A;