vitamin

vitamin An organic substance that naturally occurs in plants or animal tissue that is essential for normal metabolism of the body and to life. Vitamins play a part in dozens of crucial activities in the body: Some are antioxidants, preventing oxidation of cells and potentially preventing cancer; others permit or deny chemical reactions involved in sight, brain function, metabolism, nucleic acid synthesis, and the like. All vitamins are either available in food or can be made within the body. However, many people do not eat a diet that contains the minimum daily requirements of certain vitamins. Nutritionists suggest that the best way to ensure appropriate doses of vitamins is to eat a healthful diet, particularly one that is rich in green, leafy vegetables and carotene compounds. These foods offer many benefits that vitamin supplements cannot, including fiber, and probably include vitamin-like substances that have not yet been isolated. Lack of specific vitamins can lead to deficiency syndromes, such as rickets, beriberi, and anemia. Overconsumption of certain vitamins can also have consequences, ranging from minor to life threatening. Some vitamins are water soluble, and any excess is simply excreted in the urine. Others are fat-soluble and may build up in the body, potentially reaching dangerous concentrations. Vitamins may also interact with prescription and over-the-counter drugs, making them more or less potent. For these reasons, it is important to consult a physician before adding vitamin supplements to a daily regimen. See also Appendix C, “Vitamins.”