Vitamin A deficiency
Clinical Severe subclinical Moderate subclinical | Mild subclinical VAD under control No data available |
Vitamin A deficiency (VAD) or hypovitaminosis A is a lack of vitamin A in blood and tissues.[1] It is common in poorer countries, especially among children and women of reproductive age, but is rarely seen in more developed countries.[1] Nyctalopia (night blindness) is one of the first signs of VAD, as the vitamin has a major role in phototransduction;[1] but it is also the first symptom that is reversed when vitamin A is consumed again. Xerophthalmia, keratomalacia, and complete blindness can follow if the deficiency is more severe.[1]
Vitamin A deficiency is the world's leading cause of preventable
The prevalence of night blindness due to VAD is also high among pregnant women in many developing countries. VAD also contributes to
VAD also diminishes the ability to fight infections.
VAD is estimated to affect about one-third of children under the age of five around the world.[8] It is estimated to claim the lives of 670,000 children under five annually.[9] Around 250,000–500,000 children in developing countries become blind each year owing to VAD, with the highest prevalence in Southeast Asia and Africa. According to the World Health Organization (WHO), VAD is under control in the United States, but in developing countries, VAD is a significant concern. Globally, 65% of all children aged 6 to 59 months received two doses of vitamin A in 2013, fully protecting them against VAD (80% in the least developed countries).[10]
Signs and symptoms
Vitamin A deficiency is the most common cause of blindness in developing countries. The WHO estimated in 1995 that 13.8 million children had some degree of visual loss related to VAD.
Night blindness
A process called dark adaptation typically causes an increase in photopigment amounts in response to low levels of illumination. This occurs to an enormous magnitude, increasing light sensitivity by up to 100,000 times its sensitivity in normal daylight conditions. VAD affects vision by inhibiting the production of rhodopsin, the photopigment responsible for sensing low-light situations. Rhodopsin is found in the retina and is composed of retinal (an active form of vitamin A) and opsin (a protein).
Night blindness caused by VAD has been associated with the loss of goblet cells in the conjunctiva, a membrane covering the outer surface of the eye. Goblet cells are responsible for secretion of mucus, and their absence results in xerophthalmia, a condition where the eyes fail to produce tears. Dead epithelial and microbial cells accumulate on the conjunctiva and form debris that can lead to infection and possibly blindness.[13]
Decreasing night blindness requires the improvement of vitamin A status in at-risk populations. Supplements and fortification of food have been shown to be effective interventions. Supplement treatment for night blindness includes massive doses of vitamin A (200,000 IU) in the form of retinyl palmitate to be taken by mouth, which is administered two to four times a year.
Infection
Along with poor diet, infection and disease are common in many developing communities.[1] Infection depletes vitamin A reserves which in turn make the affected individual more susceptible to further infection.[1] Increased incidence of xerophthalmia has been observed after an outbreak of measles, with mortality correlated with severity of eye disease.[1] In longitudinal studies of preschool children, susceptibility to disease increased substantially when severe VAD was present.[1]
The reason for the increased infection rate in vitamin A deficient individuals is that
Causes
In addition to dietary problems, other causes of VAD are known.
Diagnosis
Initial assessment may be made based on clinical signs of VAD.
Vitamin A sources
Food | |
---|---|
cod liver oil | 30,000 |
beef liver (cooked) | 4,970 — 21,145 |
chicken liver (cooked) | 4,296 |
butter (stick) | 684 |
cheddar cheese | 316 |
egg (cooked) |
140 |
Vitamin A is found in many foods.[25] Vitamin A in food exists either as preformed retinol – an active form of vitamin A – found in animal liver, dairy and egg products, and some fortified foods, or as provitamin A carotenoids, which are plant pigments digested into vitamin A after consuming carotenoid-rich plant foods, typically in red, orange, or yellow colors.[26] Carotenoid pigments may be masked by chlorophylls in dark green leaf vegetables, such as spinach. The relatively low bioavailability of plant-food carotenoids results partly from binding to proteins – chopping, homogenizing or cooking disrupts the plant proteins, increasing provitamin A carotenoid bioavailability.[26]
Vegetarian and vegan diets can provide sufficient vitamin A in the form of provitamin A carotenoids if the diet contains carrots, carrot juice, sweet potatoes, green leafy vegetables such as spinach and kale, and other carotenoid-rich foods. In the U.S., the average daily intake of β-carotene is in the range 2–7 mg.[27]
Some manufactured foods and dietary supplements are sources of vitamin A or beta-carotene.[26][24]
Despite the US setting an adult upper limit of 3,000 μg/day, some companies sell vitamin A (as retinal palmitate) as a dietary supplement with amounts of 7,500 μg/day. Two examples are WonderLabs and Pure Prescriptions.[28][29]Prevention and treatment
Treatment of VAD can be undertaken with both oral vitamin A and
- As an oral form, the supplementation of vitamin A is effective for lowering the risk of birth defects.[33]
- Food fortification is also useful for improving VAD. A variety of oily and dry forms of the retinol esters, retinyl acetates, and oxidation during storage and prompt absorption of vitamin A. Beta-carotene and retinyl acetate or retinyl palmitate are used as a form of vitamin A for vitamin A fortification of fat-based foods. Fortification of sugar with retinyl palmitate as a form of vitamin A has been used extensively throughout Central America. Cereal flours, milk powder, and liquid milk are also used as food vehicles for vitamin A fortification.[34][35]
- Separated from fortification via addition of synthetic vitamin A to foods, means of fortifying foods via genetic engineering have been explored. Research on rice began in 1982.[36] The first field trials of golden rice cultivars were conducted in 2004.[37] The result was "Golden Rice", a variety of Oryza sativa rice produced through genetic engineering to biosynthesize beta-carotene, a precursor of retinol, in the edible parts of rice.[38][39] In May 2018, regulatory agencies in the United States, Canada, Australia and New Zealand had concluded that Golden Rice met food safety standards.[40] On 21 July 2021, the Philippines became the first country to officially issue the biosafety permit for commercially propagating Golden Rice.[41][42] In 2023, however, the Supreme Court of the Philippines ordered the agriculture department to stop commercial propagation of golden rice in relation to a petition filed by MASIPAG (a group of farmers and scientists), who claimed that golden rice poses risk to the health of consumers and to the environment.[43] Researchers at the U.S. Agricultural Research Service have been able to identify genetic sequences in corn that are associated with higher levels of beta-carotene, the precursor to vitamin A. They found that breeders can cross certain variations of corn to produce a crop with an 18-fold increase in beta-carotene.[44]
- Dietary diversification can also reduce risk of VAD. Non-animal sources of vitamin A like vegetables contain pro-vitamin A and account for greater than 80% of intake for most individuals in the developing world. The increase in consumption of vitamin A-rich foods of animal origin has beneficial effects on VAD.[45]
Global initiatives
Global efforts to support national governments in addressing VAD are led by the Global Alliance for Vitamin A (GAVA), which is an informal partnership between
References
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- ^ a b c "Micronutrient Deficiencies: Vitamin A". World Health Organization. Archived from the original on 3 December 2013. Retrieved 12 September 2019.
- ^ "In Preventing Vitamin A Deficiency, a Little Friendly Bacteria Might Go a Long Way". Rutgers Today. 19 December 2011. Retrieved 27 October 2019.
- ^ "WHO Vitamin A deficiency | Micronutrient deficiencies". Archived from the original on 16 August 2019. Retrieved 3 March 2008.
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- ^ ISBN 92-4-154478-3.
- ^ "A world fit for children" (PDF). Archived (PDF) from the original on 12 October 2017. Retrieved 3 March 2008.
- ^ World Health Organization, Global prevalence of vitamin A deficiency in populations at risk 1995–2005, WHO global database on vitamin A deficiency.
- ^ Black RE et al., Maternal and child undernutrition: global and regional exposures and health consequences, The Lancet, 2008, 371(9608), p. 253.
- ^ a b "Vitamin A Deficiency and Supplementation UNICEF Data". Archived from the original on 11 September 2016. Retrieved 7 April 2015.
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- ^ "Untitled Document". Archived from the original on 30 July 2014. Retrieved 15 August 2014.
- ^ Underwood, Barbara A. Vitamin A Deficiency Disorders: International Efforts to Control A Preventable "Pox." J. Nutr. 134: 231S–236S, 2004.
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- ^ "Vitamin A Deficiency Clinical Presentation: History, Physical, Causes". emedicine.medscape.com. Archived from the original on 21 September 2017. Retrieved 21 September 2017.
- ^ (Combs, 1991).
- ^ Merck Manuals Professional Edition. "Vitamin A – Nutritional Disorders". merckmanuals.com. Archived from the original on 18 March 2017. Retrieved 17 March 2017.
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- ^ a b "Diagnosis and Treatment of Vitamin A Deficiency: Workup". Archived from the original on 6 July 2017. Retrieved 1 November 2019.
- ^ ISBN 0-309-07290-5.
- ^ a b "Rank order of vitamin A content in foods, retinol activity equivalent (RAE) in ug per 100 g". FoodData Central, US Department of Agriculture. 1 October 2021. Retrieved 20 December 2021.
- ^ a b c "Vitamin A". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis. 1 July 2016. Retrieved 21 December 2021.
- ^ "USDA National Nutrient Database for Standard Reference, Release 28" (PDF). 28 October 2015. Retrieved 5 February 2022.
- ^ "Vitamin A 25,000 IU (7,500 μg)". WonderLabs. Retrieved 26 January 2022.
- ^ "Vital Nutrients Vitamin A 7,500 RAE". Pure Prescriptions. Retrieved 26 January 2022.
- ^ Beaton GH et al. Effectiveness of vitamin A supplementation in the control of young child morbidity and mortality in developing countries. United Nations Administrative Committee on Coordination, Sub-committee on Nutrition State-of-the-Art Series: Nutrition Policy Discussion Paper No. 13. Geneva, 1993.
- ^ "Distribution of vitamin A during national immunization days" (PDF). Archived from the original (PDF) on 18 October 2012. Retrieved 3 March 2008.
- ^ "WHO Vitamin A supplementation". Archived from the original on 25 January 2013. Retrieved 3 March 2008.
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- ^ FAQ: Who invented Golden Rice and how did the project start? Goldenrice.org.
- ^ LSU AgCenter Communications (2004). "'Golden Rice' Could Help Reduce Malnutrition". Archived from the original on 28 September 2007.
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- ^ "Golden Rice meets food safety standards in three global leading regulatory agencies". International Rice Research Institute – IRRI. Retrieved 30 May 2018.
- ^ Talavera C. "Philippines OKs GMO 'golden rice'". Philstar.com. Retrieved 21 August 2021.
- ^ "Filipinos soon to plant and eat Golden Rice". Philippine Rice Research Institute. 23 July 2021. Retrieved 21 August 2021.
- ^ Ordoñez, John Victor D. (20 April 2023). "SC issues Writ of Kalikasan vs Golden Rice, Bt eggplant - BusinessWorld Online". BusinessWorld. Archived from the original on 20 April 2023. Retrieved 22 August 2023.
- ^ "A New Approach that Saves Eyesight and Lives in the Developing World". USDA Agricultural Research Service. May 2010. Archived from the original on 3 March 2016. Retrieved 19 August 2010.
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Further reading
- UNICEF, Vitamin A Supplementation: A Decade of Progress, UNICEF, New York, 2007. Archived 31 October 2020 at the Wayback Machine
- Flour Fortification Initiative, GAIN, Micronutrient Initiative, USAID, The World Bank, UNICEF, Investing in the Future: A United Call to Action on Vitamin and Mineral Deficiencies, 2009. Archived 14 December 2010 at the Wayback Machine
- UNICEF, Improving Child Nutrition: The achievable imperative for global progress, UNICEF, New York, 2013.