There are two types of vitamin D, vitamin \(D_{2}\) (ergocalciferol) and vitamin \(D_{3}\) (colecalciferol). Their role is to regulate calcium and phosphate metabolism. Vitamin D mostly stands out for the fact, that together with the usual vitamin intake with food, it is synthesized in the organism through the skin i.e. endogenously. 7-dehydrocholesterol is turned into provitamin \(D_{3}\) by the action of ultraviolet sunlight and is then isomerized into vitamin D i.e. its main form 25(OH) D (25-hydroxycholecalciferol). Those reactions occur in the liver while 1,25\( \left (OH _{2} \right ) \) \(D_{3}\) (1,25-dihydroxycholecalciferol) is generated in kidneys. Metabolism of vitamin D absorbed in the colon is almost the same as the metabolism of the one that is absorbed through skin. The average need for vitamin D is 600 IU per day although this depends on the age and other factors. Some of the reasons for the lack of vitamin D are: insufficient exposure to the sun, usage of some antiepileptics, disturbance of vitamin D metabolism and insufficient intake of vitamin D with food. Recently, the role of vitamin D in the development of nervous cells as well as in many neurodegenerative diseases like multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis and epilepsy, has been discovered. In most of these diseases a lack of vitamin D has been reported, and novel studies prove that the increased intake of vitamin D diminishes some of the symptoms and has a positive impact on the aforementioned diseases.