What Is Vitamin A?
Vitamin A is actually a number of fat-soluble compounds, one of which is retinol. Retinal and retinoic acid are also components of vitamin A, but retinol is the most important one. Vitamin A comes only in animal produce, however some compounds of the vitamin A type are also found in vegetables (the most important one of these is beta-carotene) and are water-soluble.
All of the vitamin A compounds are not only fat-soluble, but are light-sensitive and easily oxidized.
What Does it Do?
Vitamin A has an important role in eye function and general health. It stops eyes becoming dry and is important in the function of the retina. It also prevents unwanted changes in the cornea. Vitamin A also maintains cell membrane stability, while the beta-carotene component has antioxidant properties. Research has indicated that there may be a connection with vitamin A and the metabolism of zinc. Zinc is a constituent of lots of enzymes. Zinc and vitamin A deficiencies often occur together in people with diseases like pancreatic disease, alcoholic cirrhosis and cystic fibrosis.
Where Do We Get It?
We mainly get vitamin A from animal products. These supply retinal, usually in combination with a fatty acid. Vitamin A is stored in both animal and fish livers, so these are good sources. Other sources include eggs, kidneys, butter and milk. Vegetable sources of vitamin A include, in particular, green, orange and yellow colored produce. Darker colored produce contains higher levels of beta-carotene. Good sources, especially, are spinach, carrots, pumpkins, sweet potato and cabbage as well as yellow and orange fruits.
How Much Do We Need?
On average, adult males need around 1000mcg daily, while adult females require around 800mcg (pregnant and lactating women need more, around 1000mcg and 1200mcg respectively). Babies and children need anything from 400-700mcg daily.
What Are The Signs And Symptoms Of Vitamin A Deficiency?
Deficiency in Vitamin A doesn't often occur in developed countries. It can happen if people have a problem with absorption (which is rare), or if they are sick, malnourished or eldery. It is, however, a major problem in developing countries. Between 250,000 and 500,000 children in developing countries are thought to go blind each year due to vitamin A deficiency.
Photo: Malnutrition and a Lack of Vitamin A can cause Bitot's Spots:
Around half of these children then die within a year. Vitamin A deficiency in children from developing countries generally tends to cause poor growth and development as well as a lack of resistance to infection.
Early symptoms of a deficiency in vitamin A include night blindness and dry eyes. Skin problems like dryness and follicular hyperkeratosis can be a sign of vitamin A deficiency, but these don't always occur.
Should We Supplement?
Fat-soluble vitamins can be toxic because we store them in the liver and fat cells. Consequently, we should be careful of taking too high a dose of vitamin A. Overdosing with vitamin A can cause fatigue, headaches, insomnia, skin problems and brittle hair. It may also negatively affect the bones. If you develop a headache that you think may be associated with vitamin A toxicity you should seek medical attention urgently.
Vitamin A toxicity can occur with doses of 30,000IUs per day in adults, and 15,000IUs per day in babies. These doses would need to be administered over several months, however.
Largely, people in developed countries who are eating a healthy, balanced diet, should not need vitamin A supplements. There are, however, certain conditions which may make supplementation useful:
Skin Conditions - Vitamin A may be beneficial to dry skin conditions and other skin problems. Beta-caretone, particularly, may be helpful to those with skin that is sensitive to the sun.
Ulcers - Vitamin A may help to prevent stress-induced ulcers, or those brought on by the use of steroids. It has also been used as a treatment for gastric ulcers.
Gynaecological Conditions - Vitamin A may help with premenstrual tension and heavy and/or painful periods.
Cancers - Certain sorts of cancer, such as lung cancer in particular, have been linked with low vitamin A levels. Other cancers which may be associated with a lack of vitamin A include mouth, stomach, prostate, cervical and colon cancer.
It is important to remember that excessive supplementation with vitamin A can be harmful, particularly if you are pregnant. It is always best to seek the advice of a doctor if you have any of these problems. It is probably best to increase your intake naturally with the consumption of foods high in vitamin A content.