Myth: Vitamin A is toxic. No one should take more than 10,000 IU per day without a prescription.
Truth: That doesn’t make any sense. There are 90,000 IU of vitamin A in six ounces of fried beef liver, and you don’t need a prescription to eat that.
In Canada the nonprescriptive limite for vitamin A is 10,000 IU. In the UK the nonprescriptive limit is 50,000 IU. In the U.S.A there is no nonprescriptive limit. Does that mean that toxicity is a function of geographical location?
Every substance is toxic if you get too much of it, including water, sunlight and oxygen. The margin of safety for vitamin A, however, is much higher than most people expect. The Merck Manual (17th ed) stuggests that chronic toxicity may develop in adults who have been taking 100,000 IU of vitamin A over a period of months.
Massive doses (up to 350,000 IU) of vitamin A are given daily as a treatment for globular acne. No documented cases of injury have been reported as a consequence of these treatments.
Symptoms of vitamin A toxicity can include hair loss, dry rough skin, cracked lips, headaches, and generalized weakness. All of these symptoms are temporary and reversible, as soon as one stops taking the excess vitamin A.
Many years ago, there were a handful cases whereby infants became ill because their mothers inadvertently overdosed them on synthetic, water dispersible vitamin A. These mothers misunderstood the instructions; and instead of giving their babies one drop of vitamin A solution, they gave them one dropperful. All of these infants recovered. There do not seem to be any documented cases of harm from taking natural, fat soluble vitamin A.
Early Arctic explorers became very ill after eating polar bear liver, at one feeding at which they probably ingested in excess of 2 million IU of vitamin A. All of these men recovered.
Birth defects have been reported in the children of women who were given a prescription drug known as isotretinoin (etretinate, accutane). Isotretinoin is a synthetic derivative of an artificial form of vitamin A. No birth defects have ever been reported in the children of women who were taking natural vitamin A.