<unk>  is the condition of a long-term lack of a<unk> . When caused by not enough<unk>  intake it is classified as a primary deficiency, whereas when due to an underlying disorder such as malabsorption it is called a secondary deficiency. An underlying disorder may be metabolic – as in a genetic defect for converting tryptophan to niacin – or from lifestyle choices that increase<unk>  needs, such as smoking or drinking alcohol. Government guidelines on<unk> es advise certain intakes for healthy people, with specific values for women, men, babies, the elderly, and during pregnancy or breastfeeding. Many countries have mandated<unk>  food fortification programs to prevent commonly occurring<unk> es. Conversely, hypervitaminosis refers to symptoms caused by<unk>  intakes in excess of needs, especially for fat-soluble<unk> s that can accumulate in body tissues. The history of the discovery of<unk> es progressed over centuries from observations that certain conditions – for example, scurvy – could be prevented or treated with certain foods having high content of a necessary<unk> , to the identification and description of specific molecules essential for life and health. During the 20th century, several scientists were awarded the Nobel Prize in Physiology or Medicine or the Nobel Prize in Chemistry for their roles in the discovery of<unk> s.
Vitamin deficiency
Mineral deficiency
Chromium deficiency
Copper deficiency
Metal toxicity
Boron deficiency 
Psychogenic disease
Fluorine deficiency