Vitamin E
Vitamin E was discovered in 1922 by Herbert M. Evans and K. S. Bishop, who first noticed that laboratory rats failed to reproduce when fed a diet in which lard was the only source of fat. According to the researchers, a mysterious compound, extracted from both wheat germ and lettuce, was able to correct the problem.
For a time, the unknown component was termed the "anti-sterility factor". In 1925, however, Evans decided that, since vitamin D had recently been discovered, the new factor should be known as vitamin E. Some time later, he also proposed the name tocopherol (from two Greek words, roughly meaning childbirth).
Under either name, the new vitamin was clearly fat-soluble. Studies by Evans and his coworker Gladys A. Emerson (1903-) showed that its deficiency, in small lab animals, caused reproductive problems in both sexes, and a definite muscle dystrophy in many species. For almost three decades, however, investigators were not certain whether vitamin E had any appreciable effect on humans.
Evans and Emerson isolated vitamin E from wheat germ oil, corn oil and cotton seed oil in 1936 and its chemical synthesis was achieved by Paul Karrer (1889-1971) and his co-workers in 1938 (actually, theirchemical synthesis was achieved since the vitamin was found to consist of four very similar compounds). The investigators decided the vitamin's biochemical function was primarily a protective one--an antioxidant, it helped prevent unsaturated fatty acids from combining with oxygen, a process that tends to have damaging effects. Since cell membranes contain substantial amounts of unsaturated fatty acids, this antioxidant action clearly can play an important role in keeping tissues from breaking down (other antioxidants include vitamin C and the trace element selenium).
At first, vitamin E was believed to regulate tissue-damaging oxidation almost entirely in animals. But in the 1940s and 1950s, nutritional surveys revealed that premature infants and patients with malabsorption illnesses not only had low levels of blood tocopherol but other blood irregularities as well. In 1968, vitamin E was finally recognized as an essential nutrient for humans.
Through its pronounced antioxidant action (and perhaps through other unknown mechanisms as well), today vitamin E is believed to help maintain the structural integrity of muscle tissue and various components of the reproductive, vascular and nervous systems. The vitamin may also slow the onset of Alzheimer's disease, although after approximately seven months the disease may still progress. It may also reduce the risk of prostate cancer when taken in high doses, according to a study conducted by Demetrius Albanes of the National Cancer Institute in 1998. Exactly how this prevention occurs is unknown and will require further study. Despite the firmly-held beliefs of many food faddists, though, there is little evidence to suggest that vitamin E supplements can help repair existing damage. The vitamin is synthesized only in plants, is concentrated in the seeds, and deficiencies are rare.
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