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Vitamin A plays an important role in vision, bone health, and the immune system. Taking in too little of the vitamin can cause vision problems, dry or rough skin, and immune system deficiencies, so taking an adequate daily amount is important. Too much vitamin A, however, can also cause severe problems, ranging from visual disturbances to kidney or liver failure.
There are two types of vitamin A: preformed vitamin A and provitamin A carotenoid. Preformed vitamin A comes from animal sources, such as liver, whole milk and fortified foods. Provitamin A carotenoid makes up the majority of the consumption of the vitamin and comes from colorful fruits and vegetables. Vitamin A toxicity is typically caused by taking in too much preformed vitamin A, as it is more rapidly absorbed and slowly cleared from the body.
Vision changes are a risk of excessive vitamin A intake. Although the vitamin plays a vital role in keeping eyes healthy, an excess amount can actually cause damage. Blurred vision and sudden changes in vision are a common symptoms of vitamin A toxicity. Young children are also likely to experience double vision.
Skin chances can also occur when an individual takes too much vitamin A. While the substance is used in numerous skin care treatments to combat acne and the signs of aging, too much can cause dry skin, increased sun sensitivity, cracking at the mouth corners, and peeling. Oily hair or hair loss can also occur.
The effects of too much vitamin A are especially pronounced in infants and children. Abnormal softening of the skull bones or bulging fontanelle (the soft spot) can occur. Infants can also suffer from failure to thrive, a medical term applied to children whose current weight or overall weight gain is significantly smaller than other children of the same age and sex. Taking too much vitamin A during pregnancy can affect the development of the fetus.
Other potential effects of taking too much vitamin A include gastrointestinal upsets such as nausea, vomiting, and decreased appetite. Dizziness or loss of consciousness can occur in severe cases. Excessive vitamin A levels can cause calcium levels in the body to rise, which in turn can lead to kidney damage.
The recommended daily allowance for vitamin A is listed both in international units (IU) and micrograms of Retinola Activity Equivalents (mcg RAE) to account for the different biological activities of retinol and provitamin A carotenoid. Daily recommendations vary depending on age and sex. For example, a child between ages one and three needs about 300 mcg RAE or 1,000 IU of vitamin A per day, while an adult female needs 700 mcg RAE or 2,300 IU per day. The recommendations can change based on medical problems, so a physician should be consulted to determine the ideal amount.