A Complete Look at Vitamin A

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Vitamin A is a fat-soluble, antioxidant vitamin. It plays an important part in bone growth, vision, reproduction, and cell division. Vitamin A helps regulate ones immune system, which helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses. It also promotes healthy surface linings of the eyes and respiratory, urinary and intestinal tracts.

The dietary form of vitamin A is retinol. Retinol is one of the most usable forms of vitamin A and is found in animal foods such as liver and whole milk. It is also found in some fortified food products. Retinol can also be converted to retinal and retinoic acid, other forms of vitamin A.

Plant foods contain provitamin A carotenoids which are darkly covered pigments that can be converted into vitamin A. Common carotenoids found in food include beta-carotene, alpha-carotene, lutein, zeaxanthin, lycopene and cryptoxanthin. Beta-carotene is the most efficiently converted to vitamin A. Consumption of carotenoid-rich fruits and vegetables is encouraged for the health benefits.

Dietary intake

When retinol is digested into the body it is incorporated into chylomicrons as the ester form, and it is these particles that go to the liver. Liver cells store the vitamin A as ester and when retinol is needed in other tissues, it is de-esterifed and released into the blood as the alcohol. Retinol then attaches to a serum carrier for transport to the targeted tissues. A binding protein inside cells, cellular retinoic acid binding protein, serves to store and move retinoic acid intracellularly.

Which foods have Vitamin A?

Retinol is found in whole eggs, milk, liver, and cheese. Many fat-free and dried nonfat milks sold in the United States are fortified with vitamin A to replace the amount lost when fat is removed. There are other fortified foods such as cereals that provide vitamin A. Animal sources of vitamin A are well absorbed and used efficiently by the body.

Provitamin A carotenoids are found in darkly colored fruits and vegetables. Some examples include: carrots, spinach, cantaloupes and sweet potatoes. Plant sources of vitamin A are not as well absorbed as animal sources.

Recommended Dietary Allowance

Adult Male 19+ – 900 micrograms Age 4- 8 400 mcg
Adult Female 19+ – 700 mcg Age 1-3 300 mcg
Age 14-18 male – 900 mcg
Age 14-18female -700 mcg
Age 9-13 -600 mcg

Topical Use

Retinoic acid, retinyl palmitate, isotretinoin, tretinoin and retinol are all used medically to treat acne and keratosis pilaris.

All forms of vitamin A are used in cosmetics and medical applications for the skin. In cosmetics, vitamin A is used as anti-aging chemicals. It increases the rate of skin turnover and gives a temporary increase in collagen giving a more youthful appearance.

Vitamin A Deficiency

Deficiency of Vitamin A is common in developing countries- approximately 250,000 to 500,000 malnourished children go blind each year from it. Vitamin A deficiency is rarely seen in the United States. It is most often associated with strict dietary restrictions and excess alcohol intake. Night blindness is one of the first stages. Vitamin A deficiency contributes to blindness by making the cornea very dry and damaging the retina and cornea.

A deficiency in Vitamin A will diminish the body’s ability to fight off infections. In countries where the deficiency is common, millions of children die each year from complications of infectious diseases such as measles. Immunization programs in these areas are limited. People with vitamin A deficiency have lungs whose cell linings have lost the ability to remove disease causing organisms. This contributes to pneumonia.

There is also what is known as sub-clinical forms of vitamin A deficiency. This occurs in individuals with low storage ability of vitamin A with less obvious symptoms. This may increase a child’s risk of developing respiratory and intestinal infections, decrease growth rate, slow bone development and decrease survival rate from a serious illness. Children in the United States who are considered at risk for sub-clinical vitamin A deficiency include: toddlers and preschool age children; children living at or below poverty level; children with inadequate health care or immunizations; children living in areas with known nutritional deficiencies; recent immigrants or refugees from undeveloped countries; children with diseases in the liver, intestines or pancreas.

Excess alcohol consumption depletes stored vitamin A. It is important for people who consume a large amount of alcohol to include good sources of vitamin A in their diet. However there people should seek medical advise before they consider any supplements.

A deficiency of vitamin A can also occur with chronic diarrhea and through an overall inadequate intake. An adequate amount of protein, calories and zinc are needed to make the retinol binding protein. Vegetarians who do not consume eggs and dairy foods need provitamin A cartenoids so they should include a minimum of five servings of fruit and vegetables in their daily diet.

Vitamin A Overdose

Too much vitamin A can be harmful or fatal. Hyper-vitaminosis A refers to high storage levels of vitamin A in the body that can lead to toxic symptoms. Toxic symptoms can occur after consuming very large quantities in a short period of time. Signs of toxicity include nausea and vomiting, headaches, dizziness, blurred vision and muscular uncoordination. Symptoms of excess include: liver toxicity, dry skin, and hair loss. Excess vitamin A has also been suspected to be a contributor to osteoporosis. Researchers are now examining the link. Worldwide the highest incidence of osteoporosis is in northern Europe, where there is also a high intake of vitamin A.

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