Vitamin A toxicity is caused due to consumption of more than the recommended dose (5,000 IU) of vitamin A. It is divided into two types, namely, acute toxicity and chronic toxicity. The symptoms of its toxicity include skin discoloration, loss of hair, muscle pain, etc.
Vitamin A is a type of fat-soluble vitamin essential for proper functioning of the body. It is found in fruits, vegetables, and animal food products. Based on the source, it 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 it 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 development of 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, inclusion of this vitamin in our diet is necessary to regulate normal vision. Overall, it improves the immune system, and helps to protect the body from the onset of certain diseases.
Deficiency and Toxicity
With reference to U.S. FDA (Food and Drug Administration), the recommended daily dosage of vitamin A is 5,000 IU (international units). The deficiency of this nutrient causes eye problems, weakened immune system, skin rashes, and growth retardation (in children). In severe cases, it may lead to night blindness or complete blindness. This deficiency is treated by incorporating adequate amounts of vitamin A-rich food in the diet. Another treatment option is administration of vitamin A supplements that are available as over-the-counter dietary or nutritional supplements.
It is estimated that about 40-50 percent of adults in the United States take vitamin A supplements regularly. According to the studies conducted on vitamin A, the human body (both children and adults) lacks the mechanism to cope up or destroy excess amounts of this fat-soluble vitamin.
Due to the chemical nature of vitamin A, the body tends to store it in various cells and tissues, rather than excreting it. Hence, the toxicity of this vitamin occurs more as compared to other water-soluble vitamins. The 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 vary depending upon the severity of the condition. Overconsumption 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 the intake of foods that contain carotene. Acute 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 these supplements should be taken under the guidance of a qualified physician in order to avoid any health complications.