Brenda Khan
Vitamin A is an essential nutrient that plays a critical role in maintaining good health. It is required for various physiological processes, including growth and development, vision, immune function, and reproduction. While vitamin A deficiency is rare in developed countries, it is a significant issue in impoverished nations, leading to blindness and other health complications. Vitamin A can be obtained from animal sources such as liver, egg yolk, and dairy products, as well as plant sources like carrots, sweet potatoes, and mangoes. However, it is important to strike a balance as excessive vitamin A during pregnancy can be harmful. Therefore, a balanced diet that includes a variety of vitamin A-rich foods is recommended to maintain optimal health.
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What You'll Learn
Vitamin A deficiency disorders
Vitamin A is a critical vitamin that helps the body develop and function properly. Vitamin A is essential for healthy vision, metabolism, cell development, immune function, and reproductive functions.
Vitamin A deficiency is rare in the developed world due to the abundance of foods rich in vitamin A, better sanitation, water, and healthcare. However, vitamin A deficiency is a highly prevalent health concern in developing countries, where many people don't get enough food with vitamin A. Infants, children, and women who are pregnant or breastfeeding are the most at risk. Vitamin A deficiency is the leading cause of blindness in children worldwide, with an estimated 250,000 to 500,000 children becoming blind every year due to this deficiency.
The early signs of vitamin A deficiency include night blindness (nyctalopia), where one has trouble seeing in the dark but can see normally in the presence of sufficient light. As the vitamin A deficiency worsens, the whites of the eyes and the corneas can become dry, leading to xerophthalmia, where one is unable to produce tears. Foamy spots called Bitot spots may appear in the whites of the eyes, and open sores on the corneas (corneal ulcers) may develop. In its more severe forms, vitamin A deficiency can cause drying or clouding of the corneas (keratomalacia), leading to blindness by damaging the retina and cornea.
Vitamin A deficiency can also lead to other health complications, including impaired immune function, increasing the risk of infections, and decreased growth and bone development rates in children. It can also contribute to maternal mortality and other poor outcomes during pregnancy and lactation.
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Vision and eye health
Vitamin A is an essential nutrient that supports normal functioning but cannot be synthesised by the human body. It is critical for good vision and eye health. A deficiency in vitamin A can lead to various eye problems, including night blindness, dry eyes, corneal ulcers, and even blindness.
Night blindness, or nyctalopia, is one of the early signs of vitamin A deficiency. People with night blindness experience difficulty seeing in low light conditions but have normal vision in adequate lighting. As vitamin A deficiency progresses, the eyes can become dry, leading to a condition called xerophthalmia, where the individual is unable to produce tears. This can result in damage to the cornea, the clear outermost layer of the eye.
Vitamin A plays a crucial role in maintaining the health of the cornea. The cornea requires proper lubrication to function optimally. Vitamin A helps the eyes produce moisture, ensuring that the corneas remain lubricated and healthy. Without sufficient vitamin A, the corneas can become dry and susceptible to infection and damage.
Vitamin A also contributes to the production of mucus in the conjunctiva, a thin membrane that covers the front of the eye and lines the eyelids. This mucus acts as a protective barrier, helping to prevent infections and keeping the eyes moist and comfortable.
In addition to its role in eye lubrication and mucus production, vitamin A is essential for vision under conditions of poor lighting. The nutrient supports visual function in dimly lit environments, as famously associated with the consumption of carrots.
Vitamin A is available from both animal and plant sources. Animal sources include liver, egg yolk, dairy products, and certain fish, while plant sources such as carrots, sweet potatoes, mangoes, and papaya contain carotenoids that the body converts into vitamin A. A balanced diet that includes a variety of these vitamin A-rich foods can help maintain healthy vision and eye function.
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Immune function
Vitamin A is an essential vitamin, meaning that it supports normal functioning but cannot be synthesised by the human body. It is critical to good health, playing a role in growth and development, vision, immune function, and reproduction.
Vitamin A is the first defined vitamin and is also known as an anti-inflammatory micronutrient. It is indispensable for mammals as it cannot be synthesised. Vitamin A deficiency causes negative effects on growth, reproduction, and counteraction of pathogens. It is one of the most common micronutrient deficiencies in the world, affecting an estimated 125 million individuals. The groups at highest risk for the development of vitamin A deficiency are infants, preschool children, pregnant women, and lactating women.
Vitamin A plays a vital role in maintaining your body's natural defences. This includes the mucous barriers in your eyes, lungs, gut, and genitals, which help trap bacteria and other infectious agents. It is also involved in the production and function of white blood cells, which help capture and clear bacteria and other pathogens from your bloodstream. This means that a deficiency in vitamin A can increase your susceptibility to infections and delay your recovery when you get sick. In fact, in countries where infections like measles and malaria are common, correcting vitamin A deficiency in children has been shown to decrease the risk of dying from these diseases.
Vitamin A also plays an important role in mucus secretion, morphological formation, and functional maturation of epithelial cells. It contributes to immune development by regulating immune cell response and providing mechanistic defence. Vitamin A has been shown to have a crucial effect on the immune response. Vitamin A also has a role in the synthesis of immunoglobulins and has an important influence on humoral immunity.
Vitamin A is stored in the hepatic stellate cells in the liver, and has a wide range of physiological functions, such as regulation of carbohydrate metabolism, promoting T cell function in the immune system, and maintenance of eye functions. Carotenoids, which serve as precursors to vitamin A, play a role in immune system regulation via the retinoic acid signalling pathway.
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Growth and development
Vitamin A is an essential nutrient that plays a critical role in growth and development, making it particularly important for children. It is required for proper bone growth and development, helping to lower the risk of injury or disability. Vitamin A also supports the daily replacement of skin cells and ensures that tissues can produce mucus and provide a barrier to infection. This function is particularly important in the conjunctiva, the membrane covering the front of the eye and the inner surface of the eyelids, where vitamin A helps maintain eye health and vision.
Vitamin A supports the immune system by helping to maintain normal mucous membranes in the lungs, throat, nose, and mouth, which trap bacteria and other pathogens. It is also involved in the production of white blood cells, which help the body fight infection and disease. This is especially important for children, who are more prone to infection and therefore have a higher metabolic rate and vitamin A requirement.
Vitamin A also plays a role in embryonic growth and development during pregnancy. However, excessive vitamin A consumption during pregnancy can harm the fetus, increasing the risk of birth defects, infection, and disease. For this reason, pregnant women should avoid foods containing high levels of vitamin A, such as liver and pâté.
Vitamin A deficiency can cause delayed growth and development in children. It is the leading cause of blindness in children worldwide, with between 250,000 and 500,000 children losing their sight each year due to vitamin A deficiency. Early signs of deficiency include night blindness and dry eyes, which can progress to corneal damage and blindness if left untreated.
Vitamin A can be found in a variety of foods, including fruits, vegetables, meats, fish, eggs, dairy products, and nuts. It is recommended that children consume at least 2-3 vitamin A-rich fruits and vegetables per day, along with a small amount of fat to aid absorption.
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Reproductive health
Vitamin A is an essential nutrient that supports normal functioning but cannot be synthesised by the body. It is critical to good health, playing a role in growth and development, vision, immune function, and reproduction.
Vitamin A is required for embryonic development and growth. In 1913, McCollum and Davis reported that the addition of an ether extract from egg yolk or butter could reinstate growth in rats maintained on a purified ration of casein, carbohydrates and salt mixtures. This led to the discovery of the importance of vitamin A in both male and female reproduction.
In female rats, vitamin A deficiency can cause reproduction to fail prior to implantation. In pregnant rats, vitamin A deficiency can lead to embryos forming with a collection of defects called the vitamin A deficiency syndrome or late vitamin A deficiency. In male rats, vitamin A is essential for the maintenance of the male genital tract and spermatogenesis.
In humans, vitamin A deficiency can impact female reproduction by reducing egg quality and affecting egg implantation in the womb. Vitamin A is also involved in the growth and development of many major organs and structures of the unborn child, including the skeleton, nervous system, heart, kidneys, eyes, lungs and pancreas.
Vitamin A helps maintain a healthy reproductive system in men and women. It also ensures the normal growth and development of embryos during pregnancy. However, it is important to note that consuming too much vitamin A during pregnancy may harm the growing baby. For this reason, pregnant women are advised to avoid foods with highly concentrated amounts of vitamin A, such as liver and pâté.
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Frequently asked questions
Vitamin A is critical to good health. It plays a role in growth and development, vision, immune function, and reproduction. It also helps maintain the integrity and function of all surface tissues, including the skin, the lining of the respiratory tract, the gut, the bladder, the inner ear, and the eye.
Vitamin A deficiency is rare in the Global West but is more common in the Global South. It is the leading cause of preventable blindness in children worldwide. One of the early signs of vitamin A deficiency is night blindness (nyctalopia). As the vitamin A deficiency worsens, the whites of the eyes and the corneas can become dry, leading to blindness.
There are two main sources of vitamin A: animal sources and plant sources. Animal sources include liver, fish liver, egg yolk, milk, cheese, and butter. Plant sources include mangoes, papayas, carrots, sweet potatoes, and maize.
