American scientists Herbert McLean Evans and Katherine Scott Bishop discovered vitamin E in 1922, and the substance was first synthesized in 1938 by the Swiss Nobel laureate for Chemistry, Paul Karrer. Vitamin E originally gained attention when it was found to be essential for rats during pregnancy, but is today recognized as a powerful antioxidant and a coenzyme in cellular membranes as well. Since the human body is unable to synthesize the important substance, adequate amounts of vitamin E must be consumed through dietary sources. The fat-soluble vitamin is found naturally in a wide range of foods, including nuts, seeds, eggs, leafy green vegetables, whole grains, and various oils, but may also be taken as a supplement.