Vitamin A deficiency (VAD) or hypovitaminosis is a lack of Vitamin A in the blood and tissues. One of the first signs of VAD is night blindness or nyctalopia. Between ¼ to ½ a million malnourished children in the developing world go blind each year from VAD, and it is preventable. According to the World Health Organization about 190 million pre-school aged children, and 19.1 million pregnant women around the world, have VAD (1). VAD also compromises the immune systems of young children, often leading to death. There are initiatives by UNICEF to provide supplementation to developing countries, and supplements have been given over the last 20 years, but documentation is waiting for post intervention blood sample surveys (2).
Vitamin A is a fat soluble vitamin essential for healthy living. There are two forms of vitamin A that we obtain through our foods. Pre-formed vitamin A (retinol and retinyl esters) and pro-vitamin A (carotenoids). Foods that contain pre-formed vitamin A include animal sources such as dairy, fish and meats (especially liver). The main pro-vitamin A carotenoid is beta-carotene (others are alpha-carotene and beta-cryptoxanthin); these are plant pigments which are converted into vitamin A. Both the pre-formed vitamin A and pro-vitamin A are metabolized intracellularly to make active forms of vitamin A. Most of the body’s Vitamin A is stored in the liver in the form of retinyl esters.
Vitamin A is involved in many functions in the body including vision, regulation of cell division, growth of bone tissue, immune function and activation of tumour suppressor genes. There is also new research around skin regeneration and skin cancer treatments (3).
Blood serum levels should be above 0.7 umol/L (or 20 mcg/dL), less than this reflects vitamin A inadequacy. Retinol and carotenoid levels are typically measured in plasma to assess vitamin A levels. However, plasma blood tests can be of limited use, as plasma levels typically do not decline until liver stores are almost totally gone (3). Therefore, a relative-dose test is used to indirectly assess the liver stores, in which plasma retinol levels are measured before and after administration of vitamin A, and if greater than 20% increase is observed, this indicates inadequate vitamin A levels. This may be a better method to determine recommended supplementation dosing and retesting.
The recommended daily intake (RDA) sufficient to meet the nutrient requirements of nearly all (97 – 98% of healthy adults 19 – 50 years) is 900 mcg retinol activity equivalence (RAE) for men and 700 mcg RAE for women daily.
Treatment with supplements will depend on the level of deficiency, and there is a large variation on the amount of International Units claimed on supplement labels. International Units vary depending on the source of the vitamin A, for example the 900 mcg RDI for men is equivalent to 3,000 IU if the food or supplement source is pre-formed vitamin A (retinol), but it is equivalent to 6,000 IU of beta-carotene from supplements, 18,000 IU of beta-carotene from food, or 36,000 IU of alpha-carotene or beta-cryptoxanthin from food. So a mixed diet containing 900 mcg RAE provides between 3,000 and 36,000 IU of vitamin A, depending on the food source (4).
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1. World Health Organization. (2009). Global prevalence of vitamin A deficiency in populations at risk 1995-2005: WHO global database on vitamin A deficiency.
2. Underwood, B. A. (2004). Vitamin A deficiency disorders: international efforts to control a preventable “pox”. The Journal of nutrition, 134(1), 231S-236S.
4. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press; 2001.