The fat-soluble vitamins, A, D, E and K, are more likely to be toxic than others simply because they're stored in your body for a long time. Vitamin A can be extremely toxic when taken in megadoses. Unlike vitamin D deficiency, it's rare to see vitamin A deficiency in the United States. However, vitamin A is promoted as an antioxidant, which some people believe will protect them from cancer and heart disease.
Vitamin A
Vitamin A encourages healthy bones, teeth, vision and immune system function. Vitamin A also makes the lining of your urinary, respiratory and intestinal tracts more resilient to infection. Dietary sources of vitamin A come from animals and plants, namely colorful fruits and vegetables, which contain provitamin A carotenoid. According to the University of Colorado Extension, most people get enough vitamin A from the foods they eat. In the United States, vitamin A toxicity is a more pressing concern than vitamin A deficiency.
Hypervitaminosis A
Vitamin A toxicity, or hypervitaminosis A, can result in mild symptoms, such as blurry vision, irritability and nausea. Excess vitamin A can result in more severe symptoms like anorexia, anemia, weak bones, joint pain, protruding eyes and liver damage. Symptoms that affect the skin and hair can include hair loss, sunlight sensitivity, seborrhea, yellow skin, itching and peeling. Babies exposed to too much vitamin A can be born with birth defects.
Other Information
Vitamin D, another fat-soluble vitamin, can also be toxic when consumed in large quantities. Symptoms of vitamin D toxicity may include nausea and vomiting, a decreased appetite, constipation, kidney stones and an abnormal heart rate. vitamin D toxicity is extremely rare, according to a July 2010 article published in the "New York Times." Healthy people have taken 10,000 I.U. vitamin D for longer than six months without noticing symptoms of toxicity. Most people don't meet their vitamin D through dietary sources, the "Times" goes on to state. Insufficient exposure to sunlight makes vitamin D supplementation necessary for some individuals.
Supplement Use
The tolerable upper intake of vitamin A established for adults is 3,000 mcg. Vitamin A and other nutrients promoted as antioxidants have no proven health benefits when taken in supplement form, states the National Center for Complementary and Alternative Medicine. The best way to get your daily dose of vitamin A is to eat a varied, healthy diet. Vitamin A is found in many animal and plant foods, such as milk, cheese, liver, eggs, leafy greens and vivid orange fruits and vegetables like carrots, sweet potatoes, pumpkin, apricots and winter squash.
References
- U.S. Office of Dietary Supplements: Vitamin A and Caretonoids
- Colorado State University Extension; Fat-Soluble Vitamins; J. Anderson, L. Young; August 2008
- MedlinePlus: Antioxidants
- MedlinePlus Medical Encyclopedia; Hypervitaminosis A; May 2010
- MayoClinic.com; Vitamin D: What Happens When You Get Too Much?; K. Zeratsky; December 2010
- National Center for Complementary and Alternative Medicine: Antioxidant Supplements for Health
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