disorders of nutrition
Vitamin A Excess
Introduction
Vitamin Aexcess (toxicity) can be sudden (acute), usually due to accidental ingestion by children, or chronic. 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 takingvitamin Asupplements. 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 tovitamin Ain 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 tovitamin A(retinoids) are used to treat severe acne and psoriasis. Whether takingvitamin A, beta-carotene, or retinoids helps reduce the risk of certain types of skin cancer is being studied. However, the risk of certain cancers and cardiovascular disease may be increased after taking high doses of beta-carotene supplements. Too muchvitamin Acan 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-dosevitamin Ato 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 tovitamin A) in food does not cause toxicity because carotenoids are converted tovitamin Avery 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. 