Vitamin D is a group of fat-soluble vitamins that enhances the absorption of calcium and phosphorus from the intestine and promotes their deposition into the bone. There are two main forms; Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol)
The term vitamin D applies to several members of a group of steroid prohormone molecules. Cholecalciferol is commonly known as vitamin D3, but is not a true vitamin since it can be generated in the skin of animals when light energy is absorbed. Egg yolk, fish oil, and some plants like vitamin D2 or ergo sterol is vitamin source for dietary. Vitamin D does not have significant biological activity but must be metabolized by the body to become the hormonally-active form known as 1,25-dihydroxycholecalciferol.
Vitamin D is hydrophobic and must move from blood bound to carrier proteins which is known as vitamin D-binding protein. 
A dietary inadequacy, impaired absorption, and increased excretion are caused nutrient deficiencies. In common, if sunlight is not enough, and the kidney does not transports vitamin D, there would be a vitamin D deficiency. If people have milk allergy, lactose intolerance, or strict vegetarianism then they are more prone to vitamin D deficiency easier. There are vitamin D disease like Rickets and Osteomalacia. The children easily take Rickets which there is a failure of bone tissue, and it makes bones softly and skeletal deformities. In the mid-17th century, Rickets was first discovered by British researchers. In the 1920s, biochemist Harry Steenbock identified the structure of vitamin D and metabolites by antirachitic activity. The Osteomalacia is vitamin D deficiency in adults. The Ostemalacia makes weak muscles and bones. There also are severe liver or kidney disease by vitamin D deficiency. Vitamin D also includes toxicity. If people take too much vitamin D then it results vitamin D toxicity. Exclusively breast-fed infants, dark skin, aging, fat malabsorption syndromes, inflammatory bowel disease, and obesity are the risk factors for vitamin D deficiency.
Most fresh food contains vitamin D such as salmon, tuna, and mackerel. They are good sources of vitamin D in fish liver oil. Beef liver, cheese, and egg yolk are also good source for vitamin D. All food which concern with vitamin must take vitamin D3(cholecalciferol)and vitamin D2(ergocalciferol). Many people use vitamin D to diet. Milk is very famous that it takes vitamin D a lot. Rickets, which was a bone disease in children, was big problem in the United States, but it was solved with milk.
People must take nutrient by food that provide nutrients and effect beneficially. For having g great diet, people should take fruits, vegetables, whole grains, low fat or fat free milk, and cheese. These contain vitamin D and it affects beneficial to health. Lean meats, poultry, fish, beans, eggs, and nuts are another foods for diet. Especially, Salmon and beef liver contains many vitamin D. For diet you need to check daily your calories too.
One of disease, Osteoporosis, occurs by vitamin D insufficiency. In 18 different countries, there are more than 2,600 women who take Osteoporosis. AN intestinal calcium absorption can’t be worked without enough sun exposure to vitamin D. If PTH increase which is occured when there is not enough sun exposure then it causes Osteoporotic fracture. To prevent Osteoporotic fracture, vitamin D3(cholecalciferol)is more effective than vitamin D2(ergocalciferol). Most calcium is effective to preserve bone health but there is limitation that is 1,000 to 1,200 mg /day.
Two types of cancer occur by lack of specialization and proliferation. One type cancer is called malignant and another one is analogs. The malignant is resulted by vitamin D receptors(VDR) which includes breast, lung, skin, and bone. The epidemiological studies suggests wrong research information that vitamin D has no bad effectiveness to cancer. In addition, vitamin D concerns with colorectal cancer, and breast cancer.
- Forms of vitamin D R. Bowen
- Diseases Office of Dietary Supplement
- Diseases Linus Pauling Institute
- vitamin D National Institutes of Health