Consuming too much vitamin A causes hair loss, cracked lips, dry skin, weakened bones, headaches, elevations of blood calcium levels, and an uncommon disorder characterized by increased pressure within the skull called idiopathic intracranial hypertension.
The diagnosis is based on symptoms and blood tests.
Most people recover completely when they stop taking vitamin A supplements.
Vitamin A (retinol) is necessary for the function of light-sensitive nerve cells (photoreceptors) in the eye’s retina and thus helps maintain night vision. It also helps keep the skin and the lining of the lungs, intestine, and urinary tract healthy and protects against infections. Good sources of vitamin A include fish liver oils, liver, egg yolks, butter, cream, and fortified milk. (See also Overview of Vitamins.)
Carotenoids, such as beta-carotene, are pigments in fruits and vegetables that give them their yellow, orange, or red color. Once consumed, carotenoids are slowly converted to vitamin A in the body. Carotenoids are best absorbed from cooked or homogenized vegetables served with some fat or oil. Good sources of carotenoids are dark green, yellow, and orange vegetables and yellow and orange fruits.
Drugs related to vitamin A (retinoids) are used to treat severe acne and psoriasis. Whether taking vitamin A, beta-carotene, or retinoids helps reduce the risk of certain types of skin cancer is being studied. However, the risk of certain cancers may be increased after taking high doses of beta-carotene supplements.
Too much vitamin A can have harmful effects (toxicity). For example, taking daily doses 10 times the RDA (recommended daily allowance) or greater for a period of months can cause toxicity. Sometimes toxicity results from taking special formulations of high-dose vitamin A to treat severe acne or other skin disorders. A smaller dose can cause toxicity in infants, sometimes within a few weeks. If children accidentally take a very high dose, toxicity may develop quickly.
Consuming large amounts of carotenoids (which the body converts to vitamin A) in food does not cause toxicity because carotenoids are converted to vitamin A very slowly. Usually, no symptoms occur. However, when very large amounts of carotenoids are consumed, the skin may turn a deep yellow (called carotenosis), especially on the palms and soles.
High-dose supplements of beta-carotene may increase the risk of cancer, but carotenoids consumed in fruits and vegetables do not seem to increase this risk.
Most people with vitamin A toxicity have a headache and rash.
Consuming too much vitamin A over a long period of time can cause coarse hair, partial loss of hair (including the eyebrows), cracked lips, and dry, rough skin. Chronic consumption of large doses of vitamin A can cause liver damage. It can also cause birth defects in a fetus.
Later symptoms include severe headaches and general weakness. Bone and joint pain are common, especially among children. Fractures may occur easily, especially in older people. Children may lose their appetite and not grow and develop normally. Their skin may itch. The liver and spleen may enlarge.
Consuming very large amounts of vitamin A all at once can cause drowsiness, irritability, headache, nausea, and vomiting within hours, sometimes followed by peeling of the skin. Pressure within the skull is increased, particularly in children, and vomiting occurs. Coma and death may occur unless vitamin A consumption is stopped.
Taking isotretinoin (a vitamin A derivative used to treat severe acne) during pregnancy may cause birth defects. Women who are or who may become pregnant should not consume vitamin A in amounts above the safe upper limit (3,000 micrograms) because birth defects are a risk.