Vitamin D

 Calciferol

 Vitamin D , also known as the sunshine vitamin,  is a group of fat-soluble prohormones, (a prohormone is a substance that is a precursor to a hormone, usually having minimal hormonal effect by itself) the two major forms of which are vitamin D₂ (or ergocalciferoll) and vitamin D₃ (or cholecalciferol). Vitamin D is synthesized by the action of sunlight on skin. Individuals with higher skin melanin content will  require more time in sunlight to produce the same amount of vitamin D as individuals with lower melanin content.

"The use of sunscreens with sun protective factor (SPF) of 8 inhibits more than 95 percent of vitamin D production in the skin, also there are indications that vitamin D deficiency may lead to skin cancer". Wikipedia.

Food source for Vitamin D:

Fish liver oils, cod, herring, halibut, sardines, salmon, tuna, egg yolks, butter, and  milk.

Functions of Vitamin D:

Regulates calcium and phosphorus metabolism helping to form strong bones and teeth. Protects against muscle weakness, and is involved in the regulation of the heart beat. Enhances immunity, and is necessary for normal blood clotting. Vitamin D in its role of a hormone regulates the activity of an enzyme, l-ahydroxylase which helps to convert vitamin D to its active form. Blood levels of vitamin D and calcium help to determine the amount of enzyme activity.

Deficiency signs of Vitamin D:

Childhood rickets ,  osteomalacia in adults, muscle numbness, tingling, spasms, cramps, insomnia, softening of bones and teeth, hypoparathyroidism, nervousness, myopia,  retarded growth, and skeletal abnormalities. "Vitamin D deficiency may also be linked to a number of chronic diseases, high blood pressure, cancer, tuberculosis, peridontal disease, multiple sclerosis, chronic pain, depression, schizophrenia, seasonal affective disorder, and several autoimmune disorders". Holick MF (2004). "Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease". American Journal of Clinical Nutrition Full Text 80 (6): 1678S-1688S.

Factors increasing the demand for Vitamin D:

Consumption of mineral oil, liver disorders, kidney disorders, rickets, hypoparathyrodism, lack of sun exposure, pregnancy, lactation, intestinal disorders, antacids, steroid hormones, cancer and alcohol.

Therapeutic use of Vitamin D:

Rickets, osteoporosis, osteomalacia, pregnancy, lactation, Crohn's disease, coeliac disease, arthritis, bone fractures,  and  hypoparathyrodism.  

Drug effects on Vitamin D:

Mineral oil, steroid drugs, cholestyramine,( Questran) dilantin, phenobarbital , carbamazepine, anticonvulsant drugs , phenturide, primidone, phenytoin, phenobarbitone, the hypnotic drug glutethimide and neomycin.

Dosage and toxicity of Vitamin D:

RDA 400 iu.  Vitamin D is fat soluble and stored in the liver, excessive doses result in the withdrawl of calcium and phosphorus from the bones and their deposition in the soft tissues such as blood vessels, kidneys, lungs, and heart. Early symptoms of toxicity include loss of appetite, thirst, vomiting, diarrhea, sore eyes, puritis, and urinary urgency. Exposure to sunlight does not  cause vitamin D toxicity.

Read more:Sun Helps Beat Breast Cancer