Vitamin D is fat soluble and it is known to have hormonal activities, that is to say it acts as messenger and regulator. For this reason some think of vitamin D as a hormone rather than a vitamin. But rickets in children and osteomalacia in adults are recognized as vitamin D deficiency diseases, and hence its vitamin role must be also accepted. Its principal function is regulating calcium and phosphate metabolism, i.e. promoting the uptake of calcium and phosphorus from foods, and causing the release of calcium from bones.
There are two forms of vitamin D. Ergocalciferol (D2) produced by the action of the sun on dehydrocholesterol in the skin, which the liver and kidneys convert into the active form of the vitamin, while commercial ergocalciferol is produced by the action of light on yeast. The second form is cholecalciferol (D3), found only in foods of animal origin, such as cod liver oil, kippers, mackerel, salmon, sardines, tuna, eggs, milk, etc.
- Rheumatoid arthritis
Vitamin D is potentially the most toxic of all vitamins. Very high doses for prolonged periods will necessarily cause excessive blood calcium, with anorexia, anxiety, constant thirst and urination, headache, itching, nausea, weakness and altered kidney function and kidney stones. High intakes of vitamin D may also increase the risks of heart disease. When vitamin D is combined with digotoxin, a digitalis drug, abnormal heart rhythms may result. A variety of conditions may predispose the organism to a vitamin D excess. These include,
- Addison's disease - Cancer of all types - Diuretics of the diazide kind
- Milk-alkali or Burnett's syndrome
- Osteoporosis caused from being bedridden (not post-menopausal)
- Sarcoidosis, earlier known as Boeck's sarcoid
- Tumors generating parathyroid hormones
- Vitamin A excess
Some drugs on the contrary increase the need for vitamin D. These include,
- Anti-cholesterol drugs like cholestyramine, colestipol, etc.
- Barbiturates like Amytal, Butisol, Luminal, Nembutal, Seconal, Sulfoton
- Cortisone drugs
- Laxatives like mineral oil and phenolphthalein
- The sleeping pill Doriden