Avitaminosis is any disease caused by chronic or long-term vitamin deficiency or caused by a defect in metabolic conversion, such as tryptophan to niacin. They are designated by the same letter as the vitamin. Avitaminoses include

• avitaminosis A, xerophthalmia or night blindness
• thiamine deficiency causes beriberi
• niacin deficiency causes pellagra
• avitaminosis C leads to scurvy
• vitamin D deficiency causes rickets

Conversely hypervitaminosis is the syndrome of symptoms caused by over-retention of fat-soluble vitamins in the body.