Toxicity of Vitamin A

Vitamin A is a type of fat-soluble vitamin essential for the proper functioning of the body. It is found in fruits, vegetables and animal food products. Based on the type of source, vitamin A is classified into two types, namely, retinol (preformed vitamin) and beta-carotene (provitamin A). The former is the active form of vitamin A that is derived from animal products such as liver, eggs, cheese and seafood. Beta-carotene, on the other hand, is a precursor of vitamin A and is converted into active form by the human body. It is derived from plant sources like carrot, sweet potato, tomato, orange, spinach and peach.

Vitamin A is necessary for cell growth, division and differentiation. It promotes the mucous layer of the skin and other eye tissues. The compound retinol is responsible for conducting light signals to the nerve cells of the retina. Hence, vitamin A is necessary to regulate normal vision. Overall, vitamin A improves the immune system and helps to protect the body from the onset of certain diseases and disorders.

Vitamin A: Deficiency and Toxicity

With reference to FDA (food and drug administration), the recommended daily allowance of vitamin A is 5000 IU (international units). The deficiency of vitamin A causes eye problems, weakened immune system, skin rash and growth retardation (in children). In severe cases of deficiency, it may lead to night blindness and complete blindness. Vitamin A deficiency is treated by adding adequate amount of vitamin A-rich foods in the diet plan. Another treatment option is by administering vitamin A supplements that are available as over-the-counter dietary or nutritional supplements.

In developed areas, dietary supplements of vitamin A are available as retinol or preformed type; whereas supplements are commonly found in the form of provitamin (carotenoid) in developing countries. It is estimated that about 40 - 50 percent of adults in United States administer vitamin A supplements regularly. According to medical studies conducted on vitamin A, it is observed that the human body (both children and adults) lacks the mechanism to cope up or destroy excess amount of this fat-soluble vitamin.

Due to chemical nature of vitamin A, the body tends to store it in various cells and tissues, rather than excreting in the urine or other body wastes. Hence, toxicity of vitamin A occurs more than other water-soluble vitamins. Vitamin A toxicity is either acute or chronic; acute condition is observed after a few days of excessive vitamin A consumption, while chronic toxicity is developed due to prolonged intake of vitamin A in higher doses.

The symptoms of vitamin A toxicity varies depending upon the severity of the condition. Over intake of provitamin A (carotenemia) results in yellowish-orange coloration of the palms and soles of the feet. Other than skin discoloration, there are no significant side effects of carotenemia. This condition is treated by limiting foods that contain carotene. Acute vitamin A toxicity causes bone tenderness, muscle pain (especially in the hands and feet) and mild neurological disorder like increased pressure in the intracranial portion.

In case of chronic vitamin A toxicity, notable symptoms include brittle nails, conjunctivitis, abnormal reddening of skin, liver cirrhosis, edema, peripheral neuritis (nerve inflammation) and loss of hair. Vitamin A supplements are not recommended for pregnant women without proper medical supervision, as it can lead to abnormalities in the developing fetus. It is to be noted that vitamin A supplements should be taken under the prescription of a qualified physician, in order to avoid health complications of vitamin A toxicity.