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 Vitamin A is made up of fat-soluble substances that have the biological activity of and are structurally similar to the parent substance all-trans retinol or retinol. Vitamin A is essential to growth, bone development, vision, reproduction, epithelial differentiation, brain development, pattern formation during embryogenesis, and hematopoiesis. Alpha-carotene, beta-carotene, and beta cryptoxanthin are Vitamin A’s dietary precursors. As a whole, these carotenoids are referred to as provitamin A. Retinoids include retinol and its metabolites, including retinoic acid and other structurally similar synthetic analogues that may perform different biological activities than retinol.
Vitamin A can help those suffering from conditions including:
- Anemia (for deficiency)
- Childhood disease
- Cystic fibrosis
- Leukoplakia
- Measles (for deficiency)
- Leukoplakia
- Night blindness
Dosage Recommendations
For the average person, 25,000 IU (7,500 mcg) of Vitamin A daily is safe. People with liver disease or those older than 65, should not take more than 15,000 IU of Vitamin A each day unless directed by their physician. Recommendations for pregnant women are being re-determined. Currently, experts believe that less that 10,000 IU, or 3,000 mcg is safe. Larger amounts could possibly cause birth defects.
Vitamin A Deficiency
Vitamin A deficiency occurs when people do not intake enough vegetables with beta-carotene, dairy foods, and liver. Infants born weighing 2.2 pounds or less are likely to have a deficiency. Double-blind research studies have administered shots to these infants to try to lower the risk of lung disease. Deficiency symptoms include poor night vision, higher risk of infections, dry skin, and a precancerous condition called metaplasia. Extreme deficiencies can cause blindness, but are very rare in Western countries.
Some deficiencies occur more often accompanying other conditions that lead to malabsorption. Those infected with HIV often have vitamin A deficiencies. Hypothyroidism causes a weakened ability to change beta-carotene into vitamin A. Those suffering from hypothyroidism are often advised to take vitamin A supplements (5,000-10,000 IU daily) if their bodies do not absorb sufficient amounts from their diet.
Elderly people suffering from type 2 diabetes often have a decline in vitamin A blood levels due to their age and despite sufficient dietary intake.
Supporting Literature
Tyson JE, Wright LL, Oh W, et al. Vitamin A supplementation for extremely-low-birth-weight infants. N Engl J Med 1999;340:1962–1968.
Rothman KJ, Moore LL, Singer MR, et al. Teratogenicity of high vitamin A intake. N Engl J Med 1995;333:1369–1373.
Azais-Braesco V, Pascal G. Vitamin A in pregnancy: requirements and safety limits. Am J Clin Nutr 2000;71(5):1325S–1333S.
Wiegand UW, Hartmann S, Hummler H. Safety of vitamin A: recent results. Int J Vitam Nutr Res 1998;68:411–416.
Cartmel B, Moon TE, Levine N. Effects of long-term intake of retinol on selected clinical and laboratory indexes. Am J Clin Nutr 1999;69:937–943.
Binkley N, Krueger D. Hypervitaminosis A and bone. Nutr Rev 2000;58:138–144.
Muñoz EC, Rosado JL, Lopez P, et al. Iron and zinc supplementation improves indicators of vitamin A status of Mexican preschoolers. Am J Clin Nutr 2000;71:789–794.
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