How much vitamin A does the human body need

Infants, children, and teenagers need more vitamin A than adults to help their developing bones and teeth. However, recommended amounts of the vitamin are based on body weight, and increase from 400 micrograms of retinol equivalents for an average one-year-old child to 1,000 micrograms for teenage boys and 800 for, teenage girls. Excess amounts of this vitamin can cause glare blindness, loss of appetite, irritability, loss of hair, headaches, joint pain, and nausea. Prolonged megadosing can lead to an increase in pressure inside the skull and even to death.

Most vitamin A overdoses occur when children are given a high-potency vitamin supplement. No one should take more than the RDA of vitamin A except on the advice of his physician, after proper evaluation by that physician. Anyone taking 25,000 or more units of vitamin A daily should have his blood vitamin-A level measured at regular intervals to determine if the blood vitamin A is rising to toxic levels.

True vitamin A, or retinol, is supplied by animal products such as liver, fish oils, milk, and butter. Carotene, found in many fruits and vegetables, is a provitamin, or a vitamin precursor, which the body converts into vitamin A. Too much carotene, while it can cause yellowing of the skin, does not lead to vitamin A poisoning. Foods fortified with vitamin A contain the same form of the vitamin as found in vitamin pills, and eating excessive amounts of vitamin A in any product can be toxic. Deep-yellow vegetables such as pumpkin, squash, carrots, or yams, and leafy greens such as spinach and broccoli are excellent sources of vitamin A. Cantaloupe, apricots, and mangoes are also high in vitamin A.