Vitamin D

Vitamin D is a fat-soluble steroid hormone precursor that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream. Strictly speaking, it is not a vitamin, but is referred to as one for historical reasons.

Related Topics:
Fat - Steroid - Hormone - Calcium - Phosphorus - Vitamin

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Often known as calciferol.

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Forms of Vitamin D:

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• Vitamin D₁: lamisterol
• Vitamin D₂: ergocalciferol (made from ergosterol)
• Vitamin D₃: cholecalciferol (made from 7-dehydrocholesterol)
• Vitamin D₄: dihydrotachysterol (22:23-dihydrovitamin D2)
• Vitamin D₅: 7-dehydrositosterol

Vitamin D2 is derived from ergosterol in the diet, whereas vitamin D3 is derived from cholesterol via 7-dehydrocholesterol. Ultraviolet light (UVB, which is wavelengths 290 to 315 nm), found in sunlight, is responsible for the production of the vitamin - 20,000 IU in one minimal erythemal dose of exposure. However, in certain parts of the world with reduced sunlight intensity there is the possibility that the quantity of vitamin D is not always sufficient. To prevent this possibility, milk may be fortified with vitamin D2. A deficiency of vitamin D leads to rickets, which is a softening of the bones owing to faulty mineralization.

Related Topics:
Ergosterol - Cholesterol - 7-dehydrocholesterol - Ultraviolet light - Erythemal - Milk - Rickets

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The active form of the vitamin is calcitriol which is synthesized from either D2 or D3 in the kidneys. Calcitriol binds to a protein transcription factor which then regulates gene expression. The outcome is the maintenance of calcium and phosphorus levels in the bone and blood with the assistance of parathyroid hormone and calcitonin.

Related Topics:
Calcitriol - Kidney - Protein transcription factor - Calcium - Phosphorus - Bone - Blood - Parathyroid hormone - Calcitonin

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Vitamin D deficiency is known to cause several bone diseases, due to insufficient calcium in the bones:

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• Rickets: a childhood disease characterized by "soft" bones
• Osteoporosis: a condition characterized by fragile bones.
• Osteomalacia: a bone-thinning disorder in adults that is similar to rickets.

Pioneering work in isolating vitamin D and determining its role in rickets was done by Edward Mellanby in 1918-1920.

Related Topics:
Edward Mellanby - 1918 - 1920

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Vitamin D malnutrition may also be linked to chronic diseases such as cancer (breast, ovarian, colon, prostate, lung and skin), chronic pain, weakness, chronic fatigue, autoimmune diseases like multiple sclerosis and Type 1 diabetes, high blood pressure, mental illnesses (depression, seasonal affective disorder and possibly schizophrenia) heart disease, rheumatoid arthritis, psoriasis, tuberculosis, periodontal disease and inflammatory bowel disease.

Related Topics:
Cancer - Breast - Ovarian - Colon - Prostate - Lung - Skin - Multiple sclerosis - Diabetes - High blood pressure - Depression - Seasonal affective disorder - Schizophrenia - Heart disease - Rheumatoid arthritis - Psoriasis - Tuberculosis

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Vitamin D: Who may need extra vitamin D to prevent a deficiency? ►