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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. Conversely hypervitaminosis is the syndrome of symptoms caused by over-retention of fat-soluble vitamins in the body. ==Types== Avitaminoses (and their lacking factors) include: *Vitamin A (retinol and carotenoid precursors) deficiency causes xerophthalmia or night blindness. *Thiamine (vitamin B1) deficiency causes beriberi. *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 megaloblastic anemia and subacute combined degeneration of spinal cord, among other conditions. *Vitamin C (ascorbic acid) deficiency leads to scurvy. *Vitamin D (cholecalciferol) deficiency is a known cause of rickets, and has been linked to numerous health problems. *Vitamin E 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Avitaminosis」の詳細全文を読む スポンサード リンク
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