Hypervitaminosis refers to a condition of abnormally high storage levels of vitamins, which can lead to toxic symptoms. The medical names of the different conditions are derived from the vitamin involved: an excess of vitamin A, for example, is called hypervitaminosis A. Generally, toxic levels of vitamins are achieved through high supplement intake and not from dietary sources. Toxicities of fat-soluble vitamins can also be caused by a large intake of highly fortified foods, but foods rarely deliver dangerous levels of fat-soluble vitamins. The Dietary Reference Intake recommendations from the United States Department of Agriculture define a “tolerable upper intake level” for most vitamins. High dosage vitamin A; high dosage, slow release vitamin B3; and very high dosage vitamin B6 alone (i.e. without vitamin B complex) are sometimes associated with vitamin side effects that usually rapidly cease with supplement reduction or cessation.