Vitamin A - The Eye Vitamin

Many people know vitamin A as the eye vitamin. This is because a deficiency can cause problems with vision, particularly at night. It is also plays an important role in several immune system functions as well as maintaining healthy skin. In addition, studies have shown that it has promise in protecting against environmental pollution and even cancer. Like vitamins C and E, it has been shown to have strong anti-oxidant properties.  Those looking to lose weight and get fit will especially appreciate this vitamin as it is also known to boost overall energy levels.

There are two compounds that form this vitamin - retinoids (preformed vitamin A) and carotenoids such as beta carotene (precursors of vitamin A that the body converts into active vitamin A). Beta carotene is easily converted into vitamin A in the body and unlike the preformed version, it is non-toxic.  In addition, beta carotene has been found to have its own unique antioxidant properties. 

Food Sources
Active vitamin A is only found in animal sources.  Foods rich in the active form include liver, milk and eggs. Beta carotene sources are only found in green and yellow-orange fruits and vegetables.  The most famous source of beta carotene is carrots.  Other sources of beta carotene include spinach, apricots and cantaloupe.

Recommended Dosage
The Reference Daily Intake (RDI) is 5000 IU. This is the level recommended to avoid deficiency. Many nutritionists, however, recommend that men who are trying to lose weight or increase their fitness level take higher doses.  To avoid toxicity and to take advantage of the additional antioxidant properties of beta carotene, it is best to get at least half of the RDI in the form of beta carotene.

Supplements
Vitamin A supplements are available as preformed vitamin A or as the precursor, beta carotene.  Again, it is best to meet your daily requirements with a combination of preformed vitamin A and beta carotene.

Vitamin A is best taken in combination with other vitamins such as vitamin B, C, D and E. In addition, it combines well with essential fatty acids, calcium, phosphorus and zinc.

Vitamin A supplements should be stored in a cool, dry place to avoid breakdown of this crucial nutrient.

Side Effects & Toxicity
Toxic effects have been noted with active vitamin A in excess of 15000 IU. Signs of toxicity include nausea, dizziness, problems with menstrual cycles, irritability, vomiting, headaches, hair loss, changes in the skin, bone pain and muscle aches. In addition, the high lipid concentration caused by excessive amounts can cause damage to the liver and spleen.

Beta carotene can be taken in large amounts for long periods of time virtually without risk of toxicity. The only adverse effect of taking too much beta carotene is the possibility of carotenemia - a harmless condition in which the skin turns a slight orange color.

Symptoms of Deficiency
Symptoms of deficiency are most commonly noticed in the form of eye and vision problems. People deficient in vitamin A may notice a dryness of the cornea as well as difficulties with night vision. Severe cases of deficiency can lead to an ulceration of the cornea which can result in blindness.

Other signs of deficiency include abscesses, sinus problems, susceptibility to allergies, frequent colds and respiratory problems. Other manifestations of vitamin A deficiency can include skin problems like acne, scalp dryness and boils, as well as insomnia, weight loss and fatigue.