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Like all vitamins, Vitamin A is essential and cannot be made by the body in the amount required to maintain health. This vitamin is involved in gene transcription and therefore is essential in all cells. It has strong antioxidant activity and is particularly important for eye and skin health, immune system function and bone health. In addition, it is thought that this vitamin plays an important role in reproduction, in reproductive health and in the breastfeeding of infants. Vitamin A is known in its precursor form as beta-carotene and in its active form as retinol.
People who do not have an adequate intake of the A vitamin tend to be more susceptible to infection and are more likely to experience severe symptoms in the event of a cold, flu or other type of non-serious infection. In addition, vision problems and reduced night vision also can develop. People with a vitamin A deficiency are at increased risk of nyctalopia, or night-blindness. This condition makes it difficult or impossible to see in low light. Another risk is an eye disease called keratomalacia, which causes the corneas of the eyes to become very dry, irritated and cloudy.
As with most other vitamins and minerals, the best way to get the recommended healthy amount of vitamin A is by eating a wide variety of foods. Many foods are rich sources of this essential vitamin, including animal sources such as meat, eggs, cheese, milk and certain types of fish. In addition, carrots, pumpkin, sweet potatoes, cantaloupe, broccoli, spinach and apricots are all good sources of beta-carotene. Vitamin A is fat-soluble, which means the body can store a supply of this vitamin in the liver. It also means that the vitamin is best absorbed by the body when eaten as part of a meal that contains fat.
Although it is essential for good health, vitamin A can be toxic in very large doses. The disease caused by toxicity is known as hypervitaminosis A, and it can cause birth defects, liver problems, hair loss, skin discoloration, skin dryness and high intracranial blood pressure. In addition, this disease can increase the risk of osteoporosis. Hypervitaminosis A occurs when the amount of the vitamin in the body exceeds the amount that the liver can store, causing the excess to enter into circulation throughout the body. In most cases, this toxicity is due to over-consumption of vitamin supplements containing large doses of vitamin A.