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A vitamin deficiency can cause a disease or syndrome known as an avitaminosis or hypovitaminosis. This usually refers to a long-term deficiency of a vitamin. When caused by inadequate nutrition it can be classed as a primary deficiency, and when due to an underlying disorder such as malabsorption it can be classed as a secondary deficiency. An underlying disorder may be metabolic as in a defect converting tryptophan to niacin. It can also be the result of lifestyle choices including smoking and alcohol consumption.
Examples are vitamin A deficiency, folate deficiency, (scurvy), vitamin D deficiency, vitamin E deficiency, and vitamin K deficiency. In the medical literature, any of these may also be called by names on the pattern of hypovitaminosis or avitaminosis + [letter of vitamin], for example, hypovitaminosis A, hypovitaminosis C, hypovitaminosis D.
Conversely hypervitaminosis is the syndrome of symptoms caused by over-retention of fat-soluble vitamins in the body.
- Vitamin A is important in growth and development, in the immune system and in eyesight. Its deficiency can cause problems in these areas, particularly in vision, notably night blindness and xerophthalmia.
- Thiamine (vitamin B1) deficiency can cause beriberi and Wernicke–Korsakoff syndrome.
- Riboflavin deficiency (vitamin B2) causes ariboflavinosis.
- Niacin (vitamin B3) deficiency causes pellagra.
- Pantothenic acid (vitamin B5) deficiency causes chronic paresthesia.
- Biotin (vitamin B7) deficiency negatively affects fertility and hair/skin growth. Deficiency can be caused by poor diet or genetic factors (such as mutations in the BTD gene, see multiple carboxylase deficiency).
- Folate (vitamin B9) deficiency is associated with numerous health problems. Fortification of certain foods with folate has drastically reduced the incidence of neural tube defects in countries where such fortification takes place. Deficiency can result from poor diet or genetic factors (such as mutations in the MTHFR gene that lead to compromised folate metabolism).
- Vitamin B12 (cobalamin) deficiency can lead to pernicious anemia, megaloblastic anemia, subacute combined degeneration of spinal cord,and methylmalonic acidemia among other conditions.
- Vitamin C (ascorbic acid) short-term deficiency can lead to weakness, weight loss and general aches and pains. Longer-term depletion may affect the connective tissue. Persistent vitamin C deficiency leads to scurvy.
- Vitamin D (cholecalciferol) deficiency is a known cause of rickets, and has been linked to numerous health problems.
- Vitamin E deficiency causes nerve problems due to poor conduction of electrical impulses along nerves due to changes in nerve membrane structure and function.
- Vitamin K (phylloquinone or menaquinone) deficiency causes impaired coagulation and has also been implicated in osteoporosis.
- Essential nutrient
- Illnesses related to poor nutrition
- Vitamin#Human vitamins for more details.
- Orthomolecular medicine