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                                        Vitamin A


Vitamin A is the name of a group of fat-soluble retinoids, including retinol, retinal, and retinyl esters .



Whats it used for?

Vitamin A is involved in immune function, vision, reproduction, and cellular communication.

Vitamin A is critical for vision as an essential component of rhodopsin, a protein that absorbs light in the retinal receptors, and because it supports the normal differentiation and functioning of the conjunctival membranes and cornea. Vitamin A also supports cell growth and differentiation, playing a critical role in the normal formation and maintenance of the heart, lungs, kidneys, and other organs .

helping your body's natural defence against illness and infection (the immune system) work properly

helping vision in dim light

keeping skin and the lining of some parts of the body, such as the nose, healthy


Good sources of vitamin A include:

cheese

eggs

oily fish

fortified low-fat spreads

milk and yoghurt

liver and liver products such as liver pâté – this is a particularly rich source of vitamin A, so you may be at risk of having too much vitamin A if you have it more than once a week (this is particularly important if you're pregnant)

You can get vitamin A by including good sources of beta-carotene in your diet, as the body can change this into vitamin A.

The main food sources of beta-carotene are:

yellow, red and green (leafy) vegetables, such as spinach, carrots, sweet potatoes and red peppers

yellow fruit, such as mango, papaya and apricots

Two forms of vitamin A are available in the human diet: preformed vitamin A (retinol and its esterified form, retinyl ester) and provitamin A carotenoids. Preformed vitamin A is found in foods from animal sources, including dairy products, fish, and meat (especially liver). By far the most important provitamin A carotenoid is beta-carotene; other provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin. The body converts these plant pigments into vitamin A. Both provitamin A and preformed vitamin A must be metabolized intracellularly to retinal and retinoic acid, the active forms of vitamin A, to support the vitamin’s important biological functions . Other carotenoids found in food, such as lycopene, lutein, and zeaxanthin, are not converted into vitamin A.


How does it work:

The various forms of vitamin A are solubilized into micelles in the intestinal lumen and absorbed by duodenal mucosal cells. Both retinyl esters and provitamin A carotenoids are converted to retinol, which is oxidized to retinal and then to retinoic acid . Most of the body’s vitamin A is stored in the liver in the form of retinyl esters.


Deficiency :

A plasma retinol concentration lower than 0.70 micromoles/L (or 20 micrograms [mcg]/dL) reflects vitamin A inadequacy in a population, and concentrations of 0.70–1.05 micromoles/L could be marginal in some people . In some studies, high plasma or serum concentrations of some provitamin A carotenoids have been associated with a lower risk of various health outcomes, but these studies have not definitively demonstrated that this relationship is causal.


Cautions:

Vitamin A is LIKELY SAFE for most people when taken by mouth or given as a shot into the muscle in amounts less than 10,000 units daily.

Vitamin A is POSSBILY UNSAFE when taken by mouth in high doses. Some scientific research suggests that higher doses might increase the risk of osteoporosis and hip fracture, particularly in older people. Adults who eat low-fat dairy products, which are fortified with vitamin A, and a lot of fruits and vegetables usually do not need vitamin A supplements or multivitamins that contain vitamin A.

Long-term use of large amounts of vitamin A might cause serious side effects including fatigue, irritability, mental changes, anorexia, stomach discomfort, nausea, vomiting, mild fever, excessive sweating, and many other side effects. In women who have passed menopause, taking too much vitamin A can increase the risk of osteoporosis and hip fracture.

There is growing concern that taking high doses of antioxidant supplements such as vitamin A might do more harm than good. Some research shows that taking high doses of vitamin A supplements might increase the chance of death from all causes and possibly other serious side effects.

Vitamin A is LIKELY SAFE for children when taken in the recommended amounts. The maximum amounts of vitamin A that are safe for children are based on age:

Less than 2000 units/day in children up to 3 years old.

Less than 3000 units/day in children ages 4 to 8 years old.

Less than 5700 units/day in children ages 9 to 13 years old.

Less than 9300 units/day in children ages 14 to 18 years old.

Vitamin A is POSSIBLY UNSAFE for children when taken by mouth in high doses. When amounts greater than those recommended are taken, side effects can include irritability, sleepiness, vomiting, diarrhea, loss of consciousness, headache, vision problems, peeling skin, increased risk of pneumonia and diarrhea, and other problems.



Special Precautions & Warnings:

Pregnancy and breast-feeding: Vitamin A is LIKELY SAFE for pregnant or breast-feeding women when taken in recommended amounts of less than 10,000 units per day. Larger amounts are POSSIBLY UNSAFE. Vitamin A can cause birth defects. It is especially important for pregnant women to monitor their intake of vitamin A from all sources during the first three months of pregnancy. Forms of vitamin A are found in several foods including animal products, primarily liver, some fortified breakfast cereals, and dietary 

supplements.

Excessive use of alcohol: Drinking alcohol may increase vitamin A’s potentially harmful effects on the liver.

Disorders in which the body does not absorb fat properly: People with conditions that affect fat absorption, such as celiac disease, short gut syndrome, jaundice, cystic fibrosis, pancreatic disease, and cirrhosis of the liver, are not able to absorb vitamin A properly. To improve vitamin A absorption, these people should use vitamin A preparations that are water-soluble.

A type of high cholesterol called "Type V hyperlipoproteinemia:" This condition might increase the chance of vitamin A poisoning. Do not take vitamin A if you have this condition.

Intestinal infections: Intestinal infections such as hookworm can reduce how much vitamin A the body absorbs.

Liver disease: Too much vitamin A might make liver disease worse. Do not take vitamin A if you have liver disease.

Malnutrition: In people with severe protein malnutrition, taking vitamin A might result in having too much vitamin A in the body.

Zinc deficiency: Zinc deficiency might cause symptoms of vitamin A deficiency to occur. Taking a combination of vitamin A and zinc supplements might be necessary to improve this condition.