Hypovitaminosis is the collective name for the conditions caused by lack or shortage of one or more specific vitamins in an organism. It may occur when and organism fails to receive the normally necessary amounts of the vitamin or vitamins or when an organism's particularly high requirement in a certain vitamin is not met. The former deficiency is referred to as primary vitamindeficiency, while the latter is known as secondary vitamin deficiency. Both deficiencies lead to low levels of the vitamin being present in the organism's blood and tissue, which can cause disturbances in the biochemical functions of the cells. If the condition is not reversed, the cell structure itself may be affected, with consequences for the function of major organs. The more advanced stages of hypovitaminosis may be characterized by secondary effects such as viral infections of various systems and diseases of the central nervous system.