Vitamin A is a necessary vitamin for maintaining immune system function, rebuilding healthy cells and preventing vision problems. It is also an antioxidant that may help prevent cellular damage caused by unstable free radical molecules. Synthetic vitamin A, which is found in some vitamin supplements, may offer the same benefits as vitamin A in foods and natural supplements; however, it may also pose the risk of toxicity.
Toxicity
Synthetic vitamin A may contribute to birth defects, according to the University of Maryland Medical Center. For this reason, pregnant women should not take supplements containing synthetic vitamin A. Both synthetic and natural vitamin A may also produce toxicity in large doses. You should contact a doctor before taking multivitamins or supplements containing vitamin A.
Symptoms
Aside from the potential for birth defects, vitamin A toxicity can produce a variety of symptoms. Synthetic and natural vitamin A toxicity can cause joint pain, poor appetite, dizziness, nausea, fatigued cerebral edema, or excess fluid in your brain. Severe toxicity can contribute to hemorrhage and liver damage, and may lead to coma. A bulging fontanel, which is the soft spot of the skull, may be a sign of vitamin A toxicity in an infant.
Tolerable Upper Limit
The Food and Nutrition Board of the Institute of Medicine has established a tolerable upper limit of 3,000 micrograms, or 10,000 IU, for preformed vitamin A intake for adults, according to the Linus Pauling Institute. Toxicity in adults typically occurs with long-term intake of 8,000 to 10,000 IU per day. The tolerable upper limit for infants is 600 micrograms or 2,000 IU per day. People who are genetically at risk for high cholesterol, the elderly and frequent alcohol users may experience toxicity at doses lower than the established tolerable upper limit.
Beta-Carotene
Beta-carotene is not a vitamin, but rather, a substance that your body converts into vitamin A. Unlike natural and synthetic vitamin A, beta-carotene does not pose the risk of toxicity -- your body converts it into vitamin A as needed for cellular function. However, according to the University of Maryland Medical Center, while animal studies indicate that beta-carotene is not toxic to a fetus or a newborn, human studies are necessary to determine what levels are safe. As such, if you are pregnant or breastfeeding, take beta-carotene supplements only under the supervision of your doctor. Beta-carotene is available both as a stand-alone supplement and in multivitamins. Foods such as carrots, squash, spinach, mangoes, sweet potatoes and pumpkin are rich sources of beta-carotene.
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