Vitamins are substances that the body needs to function normally, as they participate in numerous bodily processes. As the human organism is unable to synthesise them, with the exception of vitamins D and K and biotin in smaller quantities, we need to get them with food in their final form or as provitamins. No single food contains all the vitamins so we need to consume a diverse range of food in order to cover all the vitamin requirements. Only a carefully planned diet, which includes sufficient amounts of fruit and vegetables and an optimal intake of other nutrients, can cover our body’s vitamin requirements. There are numerous causes that may lead to signs of vitamin deficiency (despite an appropriate diet), which are established on the basis of subclinical or clinical signs, food history and biochemical analyses. Vitamin deficiency can be caused by a monotonous diet, a too low energy intake and a too low nutritional density of meals, the destruction of vitamins during cooking and food preparation or during the transport and storage of food. Studies have shown that vitamins consumed with food and not as dietary supplements or in fortified foods have a greater protective effect.