Vitamin A deficiency

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Prevalence of vitamin A deficiency, 1995

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

Millennium Development Goal 4 to reduce child mortality. About 250,000 to 500,000 malnourished children in the developing world go blind each year from a deficiency of vitamin A, around half of whom die within a year of becoming blind.[2] The United Nations Special Session on Children in 2002 set a goal of the elimination of VAD by 2010.[3]

The prevalence of night blindness due to VAD is also high among pregnant women in many developing countries. VAD also contributes to

maternal mortality and other poor outcomes in pregnancy and lactation.[4][5][6][7]

VAD also diminishes the ability to fight infections.

immunized, infectious diseases such as measles have higher fatality rates.[1] As elucidated by Alfred Sommer, even mild, subclinical deficiency can also be a problem, as it may increase children's risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness.[6]

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.

kajal (surma); this is called "Imtiaz's sign".[12]

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.

beta-carotene, provides provitamin A precursors that can prevent VAD-related night blindness. However, the conversion of carotene to retinol varies from person to person and bioavailability of carotene in food varies.[16][17]

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

killer T-cells require the retinol metabolite retinoic acid to proliferate correctly.[1] Retinoic acid is a ligand for nuclear retinoic acid receptors that bind the promoter regions of specific genes,[18] thus activating transcription and stimulating T cell replication.[1] Vitamin A deficiency will often entail deficient retinol intake, resulting in a reduced number of T-cells and lymphocytes, leading to an inadequate immune response and consequently a greater susceptibility to infections.[1] In the presence of dietary deficiency of vitamin A, VAD and infections reciprocally aggravate each other.[1]

Causes

In addition to dietary problems, other causes of VAD are known.

hematopoiesis and causes rashes and typical ocular effects (e.g., xerophthalmia, night blindness).[21]

Diagnosis

Initial assessment may be made based on clinical signs of VAD.

HPLC the most reliable.[23] Measurement of plasma retinol levels is a common laboratory assay used to diagnose VAD. Other biochemical assessments include measuring plasma retinyl ester levels, plasma and urinary retonioic acid levels, and vitamin A in breast milk.[22]

Vitamin A sources

Food

μg RAE (2001)[24] per 100 g[25]

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

vitamin A palmitate
.

  • 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

WHO, and CDC. About 75% of the vitamin A required for supplementation of preschool-aged children in low- and middle-income countries is supplied through a partnership between Nutrition International and UNICEF, with support from Global Affairs Canada.[2] An estimated 1.25 million deaths due to vitamin A deficiency have been averted in 40 countries since 1998.[2] In 2013, the prevalence of vitamin A deficiency was 29% in low-income and middle-income countries, remaining highest in sub-Saharan Africa and South Asia.[46] A 2017 review (updated in 2022) found that vitamin A supplementation in children five years old and younger in 70 countries was associated with a 12% reduction in mortality rate.[47] The review reported that synthetic vitamin A supplementation may not be the best long‐term solution for vitamin A deficiency, but rather food fortification, improved food distribution programs, and crop improvement, such as for fortified rice or vitamin A-rich sweet potato, may be more effective in eradicating vitamin A deficiency.[47]

References

  1. ^ a b c d e f g h i j k l m n o "Vitamin A". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis. January 2015. Archived from the original on 27 April 2021. Retrieved 1 November 2019.
  2. ^ a b c "Micronutrient Deficiencies: Vitamin A". World Health Organization. Archived from the original on 3 December 2013. Retrieved 12 September 2019.
  3. ^ "In Preventing Vitamin A Deficiency, a Little Friendly Bacteria Might Go a Long Way". Rutgers Today. 19 December 2011. Retrieved 27 October 2019.
  4. ^ "WHO Vitamin A deficiency | Micronutrient deficiencies". Archived from the original on 16 August 2019. Retrieved 3 March 2008.
  5. .
  6. ^ .
  7. ^ "A world fit for children" (PDF). Archived (PDF) from the original on 12 October 2017. Retrieved 3 March 2008.
  8. ^ World Health Organization, Global prevalence of vitamin A deficiency in populations at risk 1995–2005, WHO global database on vitamin A deficiency.
  9. ^ Black RE et al., Maternal and child undernutrition: global and regional exposures and health consequences, The Lancet, 2008, 371(9608), p. 253.
  10. ^ a b "Vitamin A Deficiency and Supplementation UNICEF Data". Archived from the original on 11 September 2016. Retrieved 7 April 2015.
  11. PMID 7763066
    .
  12. ^ "Untitled Document". Archived from the original on 30 July 2014. Retrieved 15 August 2014.
  13. ^ Underwood, Barbara A. Vitamin A Deficiency Disorders: International Efforts to Control A Preventable "Pox." J. Nutr. 134: 231S–236S, 2004.
  14. S2CID 35416519
    .
  15. .
  16. .
  17. .
  18. .
  19. ^ "Vitamin A Deficiency Clinical Presentation: History, Physical, Causes". emedicine.medscape.com. Archived from the original on 21 September 2017. Retrieved 21 September 2017.
  20. ^ (Combs, 1991).
  21. ^ Merck Manuals Professional Edition. "Vitamin A – Nutritional Disorders". merckmanuals.com. Archived from the original on 18 March 2017. Retrieved 17 March 2017.
  22. ^
    PMID 10746353
    .
  23. ^ a b "Diagnosis and Treatment of Vitamin A Deficiency: Workup". Archived from the original on 6 July 2017. Retrieved 1 November 2019.
  24. ^ .
  25. ^ 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.
  26. ^ a b c "Vitamin A". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis. 1 July 2016. Retrieved 21 December 2021.
  27. ^ "USDA National Nutrient Database for Standard Reference, Release 28" (PDF). 28 October 2015. Retrieved 5 February 2022.
  28. ^ "Vitamin A 25,000 IU (7,500 μg)". WonderLabs. Retrieved 26 January 2022.
  29. ^ "Vital Nutrients Vitamin A 7,500 RAE". Pure Prescriptions. Retrieved 26 January 2022.
  30. ^ 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.
  31. ^ "Distribution of vitamin A during national immunization days" (PDF). Archived from the original (PDF) on 18 October 2012. Retrieved 3 March 2008.
  32. ^ "WHO Vitamin A supplementation". Archived from the original on 25 January 2013. Retrieved 3 March 2008.
  33. PMID 8463867
    .
  34. .
  35. .
  36. ^ FAQ: Who invented Golden Rice and how did the project start? Goldenrice.org.
  37. ^ LSU AgCenter Communications (2004). "'Golden Rice' Could Help Reduce Malnutrition". Archived from the original on 28 September 2007.
  38. PMID 30220919
    .
  39. .
  40. ^ "Golden Rice meets food safety standards in three global leading regulatory agencies". International Rice Research Institute – IRRI. Retrieved 30 May 2018.
  41. ^ Talavera C. "Philippines OKs GMO 'golden rice'". Philstar.com. Retrieved 21 August 2021.
  42. ^ "Filipinos soon to plant and eat Golden Rice". Philippine Rice Research Institute. 23 July 2021. Retrieved 21 August 2021.
  43. ^ 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.
  44. ^ "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.
  45. ^ "childinfo.org: Vitamin A Deficiency". Archived from the original on 18 February 2008. Retrieved 14 March 2008.
  46. PMID 26275329
    .
  47. ^ .

Further reading

External links