Vitamin E (Tocopherol) is a light yellow oil, a fat-soluble vitamin, that is actually a family of compounds, the tocopherols, found in nature. Alphatoxopherol is the most common and the most active of the seven currently described forms—alpha, beta, gamma, delta, epsilon, and zeta. Specifically, d-alpha tocopherol is the most potent form, more active than the synthetic dl-alpha tocopherol.
Vitamin E was discovered in 1922 with experiments on rats. When fed a purified diet devoid of vitamin E, the rats became infertile. Wheat germ oil added to their diet restored their fertility. Later, the oil-based substance was isolated and called the "antisterility" vitamin. (Tokos and phero are the Greek words for "offspring" and "to bear," so tocopherol literally means "to bear children.") Though there is no clear deficiency disease in humans, vitamin E is well accepted as an essential vitamin. There is some question, however, as to whether vitamin E is needed for fertility. From general public experience, though, it seems to be clear that vitamin E makes a difference to many. The average diet today contains much less natural vitamin E than it did 50 years ago; we will see soon why, and what vitamin E actually does in the body.
Alpha-tocopherol is basically stable in heat and in acids; other forms are lost in heat, with storage or freezing, or when oxidized by exposure to the air. All vitamin E's are slightly unstable in alkali and are readily used up when in contact with polyunsaturated oils or rancid fats and oils, which are protected from oxidative destruction by vitamin E. Frying oils, the processing and milling of foods, the bleaching of flours, and cooking remove much of the vitamin E content of whole foods. During the refinement and purification of vegetable oils, vitamin E is lost; the vitamin E-rich by-products of this process are used to make some of the E used in supplements.
Vitamin E is absorbed from the intestines, along with fat and bile salts, first into the lymph and then into the blood, which carries it to the liver to be used or stored. Vitamin E is not stored in the body as effectively as the other fat-soluble vitamins, A, D, and K. Over half of any excesses may be lost in the feces, but some vitamin E is stored in the fatty tissues and the liver and to a lesser degree in the heart, muscles, testes, uterus, adrenal and pituitary glands, and in the blood. Vitamin E is partially absorbed through the skin when used as an ointment or oil application. Intestinal absorption, however, is reduced somewhat with chlorine, inorganic iron, and mineral oil. Unsaturated oils and estrogen also deplete vitamin E, increasing the body’s demand for it.
Sources: Vitamin E, as its various tocopherol forms, is found in both plant and animal foods. In general, the animal sources of E are fairly poor, with some being found in butter, egg yolk, milk fat, and liver. The best sources of vitamin E are the vegetable and seed or nut oils. It was first isolated from wheat germ oil, which is still a commonly used, rich source of vitamin E.
The oil component of all grains, seeds, and nuts contain tocopherol. The protective covering or germ part of the grains is what contains the E, and this is lost easily in the milling of flour or in the refinement of grains. For the vitamin E to be preserved, extraction of the oils from nuts and seeds must be done naturally, as by cold pressing, rather than by heat or chemical extraction, used commonly in food processing. Because of these forms of processing, the average American diet has lost many of its natural sources of tocopherols, and intake is commonly very low. The cold-pressed vegetable oils are really the best source of vitamin E, and these are most healthfully used in their raw form in salad dressings and sauces rather than in cooking, since most are polyunsaturated oils, which are adversely affected by heating. With refined or cooked polyunsaturates, more vitamin E is needed to prevent oxidation, which could lead to free radical formation, the invisible, underlying cause of many diseases. Free-radical-induced changes occur at the cellular level, the primary processes leading to many chronic degenerative diseases. The vitamin E content of most foods is related to the content of linoleic and linolenic acids, our most essential fatty acids (see Chapter 4, as well as Vitamin F). Also, the content of active alpha-tocopherol varies among the different foods and oils. Safflower oil is one of the best sources, with about 90 percent of the E being the alpha variety. Corn oil has only about 10 percent alpha-tocopherol. Some other foods that contain significant amounts of vitamin E are soybeans, some margarines and shortenings made from vegetable oils, and a few vegetables, such as uncooked green peas, spinach, asparagus, kale, and cucumber; tomato and celery also have a little.