Vitamin A: Benefits, Uses, Dosage, Deficiency

What is Vitamin A?

Vitamin A is a fat-soluble vitamin that is stored in the body so you do not necessarily have to take it each day. In order to be absorbed, vitamin A needs the help of fats and minerals. Vitamin A is a group of nutritionally unsaturated hydrocarbons, which include retinol, retinal, retinoic acid, and several provitamins A carotenoids among which beta-carotene is the most important.  

Vitamin A is normally measured in iµ or µg. (international units or micrograms). Sometimes it is measured in milligrams. 

This vitamin has several tasks; it is important for growth and development and for providing good vision, especially night vision and to build bones and teeth. It is vital for the maintenance of the immune system. Vitamin A strengthens the skin and makes it healthier and better. The vitamin also helps in the production of sex hormones. 

Additionally, vitamin A helps protect your mouth, nose, throat, and lungs from infection. Adequate supply, but not an excess of vitamin A, is especially important for pregnant women and breastfeeding for normal fetal development.

Therapeutic Uses of Vitamin A 

To treat vitamin A deficiency which could occur in people with diabetes, people with an overactive thyroid, a protein deficiency, liver disease, cystic fibrosis, and abetalipoproteinemia. 

Vitamin A is used in treating a variety of conditions and to reduce complications of diseases due to a vitamin A deficiency. Such as skin conditions including psoriasis and acute promyelocytic, leukemia, improving vision, and treating eye disorders including age-related macular degeneration and retinitis pigmentosa. Vitamin A is also used to reduce complications in diseases such as malaria, HIV, measles, and diarrhea in children.  

To reduce problems during pregnancy and after birth in malnourished women. Pharmacologic usage of various forms of retinoids does have side effects with potential toxicities. Any treatment should be avoided during pregnancy. Retinoids must only be used under medical supervision.  

Vitamin A has been used in combination with vitamin E to speed recovery from laser eye surgery.

Vitamin A Benefits

Vitamin A plays a major role in human vision, especially in the retina. Vitamin A maintains the vitamin level to ensure that the rhodopsin level is equally maintained. It also improves eyesight and helps to differentiate between light and dark.

Vitamin A also plays a crucial role in gene transcription. It mainly contains retinoic acid, which is very important for healthy-looking skin. This is achieved by developing immature skin cells into mature epidermal cells. Vitamin A is like an outer shell of your body, which makes you immune to viruses or diseases.

This is particularly essential in the embryo development and reproduction processes. Like Vitamin D, Vitamin A is equally essential for bone development and also behaves like an antioxidant.

Vitamin A can help prevent cancer, as it can control the malignant cells. It helps the nervous system increases one’s vulnerability to infections and increases hemoglobin.

Below is a summary of the Vitamin A functions in your body:

  • Assists immune function (improves white blood cells, natural killer cells, macrophages, and T and B lymphocytes)
  • Needed for the growth and support of the skin
  • Needed to detoxify polychlorinated biphenyl (PCB; any of a group of highly toxic compounds often found in industrial waste) and dioxin
  • Reduces risk for cancer (oesophagal, bladder, stomach, and skin, as well as leukaemia and lymphoma)
  • Required for vision
  • Responsible for healthy mucous membranes
  • Strengthens bones during development

Dosage

The recommended daily allowance of vitamin A – retinol is 3000 IU (900 µg) for men and 2333 IU (700 µg) for women. Some experts think that optimal vitamin A intake should be up to four times higher than the normally recommended allowance. Children need less vitamin A but based on a weight basis. Lactating, but not pregnant women, need an extra supply of vitamin A and a recommended allowance has been set to 3500 IU.

Food Sources of Vitamin A 

Vitamin A comes from animal sources and is well absorbed and used more efficiently by the body than other sources of the vitamin. Vitamin A found in plant sources is known as provitamin A carotenoid or carotenes. These must be converted by the body into vitamin A, or retinol before they can be used. Of all of the various carotenes, beta-carotene is the one that is most easily converted to vitamin A.

In many countries margarine, skimmed milk, low-fat dairy products, and powdered milk are generally fortified with vitamin A. This is done because the vitamin is removed along with the fat. Margarine is fortified with vitamin A in order to give it the same vitamin A content as butter. 

Carotene which is found in carrots and other foods allows the body to produce vitamin A without dangerous side effects.

Large doses of carotene might produce a yellowish skin color in some individuals. The beta carotene content of the fruits and vegetables in the table is many times higher than the stated Retinol equivalent /value.

Vitamin A Deficiency 

Vitamin A deficiency can occur as either a primary or a secondary deficiency. A primary vitamin A deficiency occurs among children and adults who do not consume an adequate intake of provitamin A carotenoids from fruits and vegetables or vitamin A from animal and dairy products. Early weaning from breast milk can also increase the risk of vitamin A deficiency. 

Vitamin A deficiency, globally, is alarmingly high as it affects approximately one-third of children under the age of five around the world. It is estimated to claim the lives of nearly 700000 children under five annually. Around 250,000–500,000 children in developing countries become blind each year owing to vitamin A deficiency, with the highest prevalence in Southeast Asia and Africa. 

Lack of vitamin A is a frequent cause of blindness and increased susceptibility to infection in underdeveloped countries. 

Secondary vitamin A deficiency is associated with chronic malabsorption of lipids, impaired bile production prolonged exposure to oxidants such as cigarette smoke, and chronic alcoholism. 

Vitamin A is a fat-soluble vitamin and depends on micellar solubilization for dispersion into the small intestine. Thus a low-fat diet would result in poor use of vitamin A. Zinc deficiency can also impair the absorption, transport, and metabolism of vitamin A. Zinc is essential for the synthesis of vitamin A and as a cofactor in the conversion of retinol to retinal.  

In malnourished populations, common low intakes of vitamin A and zinc increase the severity of vitamin A deficiency and lead to physiological signs and symptoms of deficiency. 

A study has shown a major reduction in malaria morbidity with combined vitamin A and zinc supplementation in young children.

Deficiency Symptoms 

Vitamin A deficiency affects mostly children under the age of five across the globe. It can cause blindness in children. Inadequate consumption of Vitamin A can be reversed by eating fruits, vegetables and animal products rich in Vitamin A.

Since it is a fat-soluble vitamin, it depends on solubilization for dispersion into the small intestine, and the lack of this solubility is a result of Vitamin A deficiency. 

Cigarette smoke and chronic alcoholism can lead to Vitamin A deficiency. Night blindness is a common result of a deficiency of this vitamin, and the deficiency also has an effect on nursing mothers.

While excess consumption of Vitamin A can be fatal, continuous deficiency can result in a stoppage of tear formation in the eyes. It also affects the immunity of a person and leads to urinary infections, ear infections, and the formation of white lumps in hair follicles.

Developed countries like the United States are rare in having vitamin A deficiencies. In general, people who eat a balanced, varied diet shouldn’t need to focus on specific vitamins and minerals.

In adults with gastrointestinal diseases that interfere with vitamin A absorption, vitamin A deficiency can occur.

The following is a list of symptoms of Vitamin A deficiency:

  • Decreased steroid synthesis
  • Dry eyes
  • Fatigue
  • Hypothyroidism (low thyroid production)
  • Increased susceptibility to infections
  • Increased susceptibility to vaginal yeast infections
  • Night blindness
  • Poor tooth and bone function
  • Poor wound healing
  • Rough, scaly skin

Precautions and Toxicity 

Doses above 18500 IU given to infants daily for three months have caused adverse effects. Excess vitamin A, which is most common with high doses of vitamin A supplements, can cause birth defects. Therefore during pregnancy, it is important not to exceed recommended daily values. 

In general, amounts of 10000 to 20000 IU daily cause no side effects. Most people can take up to 100,000 IU daily for some time before symptoms of overdoses occur.  

Vitamin A self-medication in combination with vitamin A-rich food is the leading cause of toxicity. Toxicity in adults usually occurs only after a daily intake exceeding 300,000 IU over several months.  

There have been a few reports on the occurrence of hypervitaminosis A, when intake in the order of only 50,000 IU has been taken daily for a few years. 

Normal symptoms of overdose are usually headaches, sore eyes, and lips, dry skin, diarrhea and nausea. More severe symptoms include enlarged liver, reduced pancreas secretion, and impaired vision. People with liver disease or diabetes should contact their doctor before taking any vitamin A supplements.

Both vitamin A and beta-carotene may increase triglycerides, which are fats in the blood. They may even increase the risk of death from heart disease, particularly in smokers. 

Since vitamin A is fat-soluble, disposing of any excesses taken in through diet, takes much longer than with water-soluble B vitamins and vitamin C. This allows for toxic levels of vitamin A to accumulate. In general, acute toxicity occurs at doses of 25,000 IU/kg of body weight, with chronic toxicity occurring at 4,000 IU/kg of body weight daily for 6–15 months. However, liver toxicities can occur at levels as low as 15,000 IU per day to 1.4 million IU per day, with an average daily toxic dose of 120,000 IU per day, particularly with excessive consumption of alcohol. 

Some medications that may cause interactions: 

Anticoagulants, Cholesterol-lowering drugs, Doxorubicin, Carbamazepine and Methotreaate, Neomycin, Omeprazole, Orlistat, Olestra, Retinoids, Tylenol.

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