Vitamin A refers to a group of compounds that impact your vision, bone health, immune system and reproductive capabilities. Two categories of vitamin A exist in foods. Animal foods contain preformed vitamin A, also known as retinol. Fruits and vegetables contain carotenoids. Vitamin A toxicity is called hypervitaminosis A and is caused by consuming too much animal-based sources of vitamin A, usually in the form of supplements.
Vitamin A Sources
Animal sources of vitamin A include liver, cod liver oil, butter, milk and eggs. Plant foods high in vitamin A include sweet potatoes, pumpkins, carrots, spinach and other leafy greens. The relative strength of vitamin A depends on the food source. Plant-based vitamin A, commonly called beta-carotene, is less easily absorbed than the retinol in animal foods, according to the Linus Pauling Institute at Oregon State University.
Retinol Activity Equivalence
Retinol activity equivalence, or RAE, measures the strength of vitamin A in food relative to its most potent form, or retinol, which is the type of vitamin A in eggs and dairy products. For example, the beta-carotene in carrots has an RAE of 12:1, meaning 12 micrograms of beta-carotene are required to produce 1 microgram of retinol. This is because beta-carotene in plant foods is less easily absorbed. However, beta-carotene in oil has an RAE of 2:1, making it half as potent as animal-based vitamin A.
The Office of Dietary Supplements recommends that men consume 900 micrograms of RAE per day. This is equivalent to 3,000 IU. Women should consume 700 micrograms daily, or 2,310 IU. Exceeding the recommended intake can result in toxicity, especially if it is in the form of preformed vitamin A, or retinol in animal foods and supplements. According to the Linus Pauling Institute, toxicity can occur quickly from very high dose exposure or from consuming slightly above the recommended intake over a long period.
Tolerable Upper Level
Vitamin A toxicity usually results from consuming 10 times the recommended intake, or roughly 33,000 IU, over a long period. It is best not to exceed 10,000 IU of vitamin A per day, which is known as the tolerable upper level of intake for retinol, below which no symptoms of toxicity usually occur. However, evidence suggests that for some populations, including the elderly and alcoholics, this level might become toxic. Ask your doctor for more information on the amount of vitamin A that is right for you.
Symptoms of Toxicity
Vitamin A toxicity includes nausea, headache, fatigue and loss of appetite, and might involve dry, itchy skin, bone and joint pain. Fluid buildup around the brain, a condition known as cerebral edema, also can occur. If severe, liver damage as well as excessive bleeding and coma might result.