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The major cause of blindness in children worldwide is xerophthalmia caused by vitamin A deficiency. In addition it has other adverse effects, including increased mortality and the term vitamin A deficiency disorders (VADD) has been introduced to cover the whole clinical spectrum of disease. The ocular manifestations of xerophthalmia have been classified and a set of prevalence criteria for the detection of a problem of public health magnitude has been in use for more than two decades. The global prevalence of VADD is now well documented and World Health Organization (WHO) receives information continuously for updating its data base on the subject. The pathogenesis of the disease is still imperfectly understood, it is not at all clear precisely why certain subjects in vulnerable communities develop xerophthalmia, while the majority are spared. A schedule for treatment of the established case has been available for a long time, but at both clinic and hospital level concentrated sources of vitamin A for treatment are frequently not available. More emphasis needs to be laid on prevention and a choice of methods consisting of large dose supplementation, fortification of food, control of precipitating infections and dietary improvement. The advantages and drawbacks of each are discussed.
Title page i
Table of content v
Chapter One INTRODUCTION
Vitamin A sources 1
Symptoms of vitamin A deficiency 2
Health benefits of vitamin A 4
Chapter Two FUNTIONS OF VITAMIN A IN HUMAN METABOLIC PROCESSES
Overview of vitamin A metabolism 8
Units of expression 17
Dietary sources 19
Evidence for making recommendations 22
Determining mean requirements and setting safe level of intakes 25
Chapter Three METABOLISM OF VITAMIN A
Metabolism within the gastrointestinal tract 35
Cellular retinol-binding protein 43
Chylomicrons and their metabolism in the circulation 43
What is Vitamin A?
Vitamin A is a fat soluble vitamin that is also a powerful antioxidant. Vitamin A plays a critical role in maintaining healthy vision, neurological function, healthy skin, and more. Vitamin A- like all antioxidants- is involved in reducing inflammation through fighting free radical damage. Consuming a diet high in antioxidants is a way to naturally slow aging
Antioxidants like Vitamin A are also responsible for building strong bones, regulating gene regulation, maintaining healthy clear skin, facilitating cell differentiation, and supporting immune function. Some of the best sources of Vitamin A include eggs, milk, liver, carrots, yellow or orange vegetables such as squash, spinach, and other leafy green vegetables.
Vitamin A Sources
Vitamin A is found in two primary forms: active Vitamin A and beta carotene. Active Vitamin A comes from animal-derived foods and is called retinol. This “pre-formed” Vitamin A can be used directly by the body; it does not need to first convert the Vitamin.
The other type of Vitamin A, which is obtained from colorful fruits and vegetables, is in the form of “pro Vitamin A” carotenoids, which are converted to retinol by the body after the food is ingested. Beta carotene, a type of carotenoid which is found primarily in plants, needs to first be converted to active Vitamin A in order to be utilized by the body.
Studies have repeatedly shown that antioxidants like Vitamin A are vital to good health and longevity; they benefit eye health, boost immunity, and foster cell growth. Nutrition experts and physicians recommend obtaining antioxidants like
Vitamin A primarily by eating a well-balanced diet high in fruits, vegetables, and whole foods whenever possible, rather than from supplements.
Symptoms of Vitamin A Deficiency
Vitamin A is essential for normal vision, as well as proper bone growth, healthy skin, and protection of the mucous membranes of the digestive, respiratory, and urinary tracts against infection. People with long-term malabsorption of fats are very susceptible to developing a Vitamin A deficiency.
The most common health concerns that will cause malabsorption of vitamin A include gluten sensitivity issues, a leaky gut syndrome and auto immune responses, inflammatory bowel disease, and pancreatic disorders. Alcoholics, whose excess toxicity creates low vitamin A levels, are also at a much higher risk fr deficiency.
Vitamin A deficiency has become a public health problem in more than half of all countries, especially in Africa and South-East Asia, especially affecting young children and pregnant women in low-income countries.
This can be a serious problem for children because the lack of vitamin A causes severe visual impairment and blindness; it also increases the risk of severe illness, and even death, significantly. Children may be in harm’s way from such common childhood infections as diarrhoeal disease and measles.
Poor Eye Health
A Vitamin A deficiency can lead to a thickening of the cornea and eventually even to blindness. Keratomalacia, a condition that comes from severe deficiency of vitamin A, is a condition that is bilateral, meaning it usually affects both eyes.
This type of deficiency may be dietary, meaning your daily intake of the vitamin, or metabolic, meaning your body’s ability to absorb it. Early symptoms of Keratomalacia may include night blindness and extreme dryness of the eyes.
Your eyesight may be followed by wrinkling, cloudiness, and a softening of the corneas. If the corneas continue to soften, without adequate attention and treatment, this may lead to infected corneas, a rupture, or degenerative tissue changes- all can cause blindness.
Premature Skin Damage
Vitamin A deficiency will lead to the drying, scaling, and follicular thickening of the skin. Keratinization of the skin, when the epithelial cells lose their moisture and become hard and dry, can occur in the mucous membranes of the respiratory, gastrointestinal tract, and urinary tract.
Respiratory infections can occur because the body’s immunity is impaired by the lack of vitamin A. The younger the patient, the more severe the effects can be. Growth retardation and infections are common among children, and the mortality rate can reportedly exceed 50% in children with severe vitamin A deficiency.
A Risky Pregnancy
For pregnant women, the vitamin A demand is the highest during the last trimester; most often, women suffer from vitamin A deficiencies during this time. A pregnant woman can suffer from night blindness if her vitamin A intake is not sufficient
Health Benefits of Vitamin A
Vitamin A is a critical part of the rhodopsin molecule, which is activated when light shines on the retina, and it sends a signal to the brain, which results in vision. Beta carotene, the form of vitamin A found in plants, plays a role in preventing macular degeneration, the leading cause of age-related blindness.
In a study sponsored by the National Eye Institute, as an Age-Related Eye Disease Study, people at high risk for the disease who took a daily multiple vitamin that included vitamin A, vitamin C, vitamin E, zinc and copper, had a 25 percent reduced risk of advanced macular degeneration during a six-year period.
Studies also show that vitamin A eye drops are effective for the treatment of dry eyes. One study found that over-the-counter lubricating eye drops containing vitamin A were as effective for the treatment of dry eye syndrome as more expensive prescription eye drops formulated for dry eye relief.
Another study was done in early 2011, by researchers at Columbia University Medical Center in New York; they found that a synthetic, altered form of vitamin A might be able to slow the progression of Stargardt’s disease, an inherited eye disease that causes severe vision loss in young people.
Several immune system functions are dependent on sufficient vitamin A, which is why it is known as an important immune booting vitamin. Genes involved in immune responses are regulated by Vitamin A, which means it is essential for fighting serious conditions like cancer and autoimmune diseases, but also illnesses like the flu or common colds.
Beta-carotene is also a powerful antioxidant that can help boost the immune system and prevent a variety of chronic illnesses. Vitamin A can especially help the immunity of children. A study done in London found that vitamin A supplements reduced child mortality by 24 % in low and middle-income countries. The study also found that vitamin A deficiency in children increased their vulnerability to infections like diarrhea and measles.
Another study conducted by the Colombian health-related social security system gave 100,000 children vitamin A supplements, who typically weren’t taking any. They found that there was an estimated savings in medical costs, of $ 340,306,917 due to the number of events involving diarrhea (4,268) and malaria (76), and hospitalization, that were reduced due to the supplementation. This study concluded that it would be cost effective to use vitamin A supplements for the treatment of these medical issues in children.( 1)
Vitamin A has antioxidant properties that neutralize free radicals in the body that cause tissue and cellular damage. Vitamin A can prevent the cells from becoming overactive. When the immune system overreacts to food proteins, this is what creates food allergies and eventually inflammation. Vitamin A intake can help to lower the risk of certain types of food allergies because it helps to prevent this dangerous overreaction.
Vitamin A is necessary for wound healing and skin re-growth. It is needed to support all of the epithelial (skin) cells both internally and externally and is a powerful aid in fighting skin cancer. Vitamin is needed to form glycoproteins, a combination of sugar and protein, which help the cells bind together forming soft tissues.
A deficiency of vitamin A can lead to a poor complexion, as indicated by studies that prove that vitamin A can fight acne and improve overall skin health. Vitamin A keeps the lines and wrinkles in your skin away by producing more collagen, which is responsible for keeping the skin looking young. Vitamin A can also contribute to healthy hair.
According to a study conducted at the University of York, vitamin A intake could help treat several forms of cancer thanks to the vitamin’s ability to control malignant cells in the body. It is currently understood that retinoic acid plays important roles in cell development and differentiation as well as cancer treatment.
Lung, prostate, breast, ovarian, bladder, oral, and skin cancers have been demonstrated to be suppressed by retinoic acid. Another study collected numerous references demonstrating the findings of retinoic acid in melanoma, hepatoma, lung cancer, breast cancer, and prostate cancer. Researchers found new evidence indicating that the molecular mechanisms in retinoic acid may control cancer cells’ fates.
Since high doses of retinoic acid may lead to cytotoxicity, meaning it can be toxic to cells, so it is probably best utilized as a potential supplement in one’s daily diet to prevent or suppress cancer progression.
Keep in mind it is always best to get vitamin A from natural sources, like food, and not to overload on vitamin A supplements in hopes of preventing disease, as more is not necessarily better.
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