Vitamin A is a collective term for a group of nutrients that support aspects of your health, such as immune system regulation, the division and specialization of your cells, and normal vision and sexual reproduction. If you get too much vitamin A, you can develop a form of poisoning or toxicity called hypervitaminosis A. But eating too many vegetables will not cause hypervitaminosis A.
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Vitamin A Basics
Vitamin A can come from animal or plant sources. The animal-based form of the vitamin, also known as preformed vitamin A, comes from foods including liver, whole milk and milk products. Types of preformed vitamin A include substances called retinol, retinal and retinoic acid. Plant-based vitamin A, also known as provitamin A carotenoid or simply carotenoid, is a chemical precursor of retinol. Types of carotenoids include beta carotene, beta cryptoxanthin and alpha carotene. Vitamin A supplements can contain preformed vitamin A, provitamin A carotenoids or a mixture of the two.
Carotenoids are a group of more than 600 pigments or colorings that occur naturally in various species of plants, photosynthetic bacteria and algae. Vegetables and fruits that contain carotenoids have a characteristic red, orange or yellow color. Roughly 34 percent of the vitamin A in American women's diets comes from carotenoid sources such as carrots, tomatoes, peppers and peas. Roughly 26 percent of the vitamin A in American men's diets also comes from these sources. The main carotenoid in the American diet is beta carotene.
Vitamin A Poisoning
Hypervitaminosis A can occur if you regularly get too much vitamin A, or if you take too much of the vitamin in a short period of time. Potential consequences of long-term overconsumption include central nervous system problems, liver abnormalities, birth defects and a reduction in bone density that can lead to the disorder called osteoporosis. Potential consequences of short-term overconsumption include dizziness, headache, nausea, vomiting, loss of muscular coordination and blurred vision.
While you can develop hypervitaminosis A from consuming too much preformed vitamin A, you can't get it from consuming the carotenoids in vegetables or fruits, the Linus Pauling Institute explains. However, eating large amounts of dietary beta carotene or 30 milligrams or more per day of beta carotene supplements can lead to yellow skin discoloration. Eating too many foods or taking too many supplements that contain a carotenoid called lycopene can lead to orange discoloration of your skin. In addition, taking 20 to 30 milligrams per day of beta carotene supplements for several years can lead to increased risks of lung cancer in people who smoke or are exposed to asbestos.
While use of beta carotene is not linked to birth defects, the effects of high doses of this carotenoid during and after pregnancy are not well studied. For this reason, pregnant and lactating women should avoid taking more than 3 milligrams a day of beta carotene supplement a day without a doctor's explicit advice. Consult your doctor for more information on the causes of vitamin A poisoning.