Vitamin A
> back to About Micronutrients
Vitamin A is a fat soluble vitamin that is essential for an efficient immune system and is important in the eyes, skin, teeth, bones, and mucous membranes. Vitamin A plays a number of vital roles in the human body, including assistance in the synthesis of mucopolysaccharides, maintaining the stability and integrity of lysozomes and cell membranes, and as a precursor of retinene in the retina. The physiological roles of vitamin A include: Maintaining glucocorticoid production, supporting epithelial regeneration, improving the antibody response to T-cell antigens, increasing lymphocyte proliferation and cytokine production, proper mucosal function, proper cellular differentiation, as well as playing roles in maintaining visual and reproductive system integrity.
Vitamin A Storage and Target Tissues
While all tissues contain trace amounts of vitamin A, more than 90% of the body’s vitamin A is stored in the liver (and the kidneys to a lesser extent). Consequently, individuals with poor liver or kidney function are particularly at risk for vitamin A deficiency. Other predisposing factors include alcoholism, pancreatic, gallbladder or respiratory disease, steatorrhea, measles, acute protein deficiency, intestinal parasites, prolonged use of neomycin sulfate and/or cortisone. Children under the age of 6 are also prone to vitamin A deficiency.
Target tissues for vitamin A include the retina, skin, bone, liver, adrenals, germinal epithelium, intestines and salivary glands.
Signs and Symptoms of Vitamin A Deficiency
Vitamin A is involved in a large number of systems in the human body. Consequently, a large number of systems can be negatively affected by vitamin A deficiency. Poor epithelial regeneration can result in skin hyperkeratinization, problems with the genitourinary reproductive system (poor fertility), the gastroenterological/biliary system, the pulmonary system or the digestive tract. The effects of vitamin A deficiency on the retina can result in night blindness and/or epithelial degeneration in the eye. The effect of vitamin A deficiency on the immune system can result in low lymphocyte count and impaired immune response, as well as poor antioxidant function. The developing skeletal system also requires vitamin A, and a deficiency in this nutrient can result in growth retardation as well as abnormal bone development.
Vitamin A Requirements and Replenishment
The recommended daily allowance (RDA) for vitamin A has been based on the amount needed to correct night blindness in people with vitamin A deficiency, and the amount needed to raise plasma vitamin A levels to normal levels in vitamin A deficient individuals. The highest dietary sources of vitamin A are in fish liver oil and animal livers and kidneys. Carrots, tomatoes, orange fruits and green vegetables, palm oil, and dairy products (with the exception of cottage cheese) are also good dietary sources of vitamin A.
Vitamin A Toxicity
Vitamin A is toxic if taken in excess over an extended period of time. Taking more than 30,000 ug RE/day of vitamin A over a prolonged period is generally considered toxic. Pregnant individuals should be particularly careful to avoid excess vitamin A intake (more than 800 ug RE/day), as it is a known morphogen, and can cause abnormal fetal development at dosages above 4800 ug RE/day.
Signs of vitamin A toxicity include peeling/itching of the skin, brittle nails, yellowish skin coloration (carotene only), hair loss (alopecia), anorexia, gingivitis, delayed blood clotting and decreased vitamin K absorption, elevated serum alkaline phosphatase, hypercalcemia, bone/joint pain, hyperostosis, premature epiphysis closure (during growth), osteoporosis and increased risk of hip fractures. Other symptoms include unusual blood pressure in the eyes (papilledema), blurred vision, light sensitivity, headaches, irritability, fatigue, and insomnia.
> back to top
> back to About Micronutrients
Vitamin A is a fat soluble vitamin that is essential for an efficient immune system and is important in the eyes, skin, teeth, bones, and mucous membranes. Vitamin A plays a number of vital roles in the human body, including assistance in the synthesis of mucopolysaccharides, maintaining the stability and integrity of lysozomes and cell membranes, and as a precursor of retinene in the retina. The physiological roles of vitamin A include: Maintaining glucocorticoid production, supporting epithelial regeneration, improving the antibody response to T-cell antigens, increasing lymphocyte proliferation and cytokine production, proper mucosal function, proper cellular differentiation, as well as playing roles in maintaining visual and reproductive system integrity.
Vitamin A Storage and Target Tissues
While all tissues contain trace amounts of vitamin A, more than 90% of the body’s vitamin A is stored in the liver (and the kidneys to a lesser extent). Consequently, individuals with poor liver or kidney function are particularly at risk for vitamin A deficiency. Other predisposing factors include alcoholism, pancreatic, gallbladder or respiratory disease, steatorrhea, measles, acute protein deficiency, intestinal parasites, prolonged use of neomycin sulfate and/or cortisone. Children under the age of 6 are also prone to vitamin A deficiency.
Target tissues for vitamin A include the retina, skin, bone, liver, adrenals, germinal epithelium, intestines and salivary glands.
Signs and Symptoms of Vitamin A Deficiency
Vitamin A is involved in a large number of systems in the human body. Consequently, a large number of systems can be negatively affected by vitamin A deficiency. Poor epithelial regeneration can result in skin hyperkeratinization, problems with the genitourinary reproductive system (poor fertility), the gastroenterological/biliary system, the pulmonary system or the digestive tract. The effects of vitamin A deficiency on the retina can result in night blindness and/or epithelial degeneration in the eye. The effect of vitamin A deficiency on the immune system can result in low lymphocyte count and impaired immune response, as well as poor antioxidant function. The developing skeletal system also requires vitamin A, and a deficiency in this nutrient can result in growth retardation as well as abnormal bone development.
Vitamin A Requirements and Replenishment
The recommended daily allowance (RDA) for vitamin A has been based on the amount needed to correct night blindness in people with vitamin A deficiency, and the amount needed to raise plasma vitamin A levels to normal levels in vitamin A deficient individuals. The highest dietary sources of vitamin A are in fish liver oil and animal livers and kidneys. Carrots, tomatoes, orange fruits and green vegetables, palm oil, and dairy products (with the exception of cottage cheese) are also good dietary sources of vitamin A.
Vitamin A Toxicity
Vitamin A is toxic if taken in excess over an extended period of time. Taking more than 30,000 ug RE/day of vitamin A over a prolonged period is generally considered toxic. Pregnant individuals should be particularly careful to avoid excess vitamin A intake (more than 800 ug RE/day), as it is a known morphogen, and can cause abnormal fetal development at dosages above 4800 ug RE/day.
Signs of vitamin A toxicity include peeling/itching of the skin, brittle nails, yellowish skin coloration (carotene only), hair loss (alopecia), anorexia, gingivitis, delayed blood clotting and decreased vitamin K absorption, elevated serum alkaline phosphatase, hypercalcemia, bone/joint pain, hyperostosis, premature epiphysis closure (during growth), osteoporosis and increased risk of hip fractures. Other symptoms include unusual blood pressure in the eyes (papilledema), blurred vision, light sensitivity, headaches, irritability, fatigue, and insomnia.
> back to top
About SpectraCell | FAQ | Lab Services | Getting Started | Research | News & Testimonials