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Tocopherols  (Vitamin E)

Introduction
The term “Vitamin E” refers to a class of lipid-soluble antioxidants consisting of four tocopherol isomers and four tocotrienol isomers. Vitamin E is present in all cell membranes, plasma lipoproteins and red blood cells. As the major lipid-soluble chain-breaking antioxidant in humans, it functions to protect proteins, DNA, low density lipoproteins (LDL) and polyunsaturated fatty acids (PUFAs) from free radical-induced oxidation. Vitamin E also quenches singlet oxygen.47 In this regard, d-alpha-tocopherol is the most biologically active isomer.47

Absorption, Metabolism and Distribution in Humans
Along with dietary fat, vitamin E is absorbed in the intestine and incorporated into chylomicrons and transported via the lymph system where it is associated with erythrocytes, very low, low and high density lipoproteins (VLDL, LDL, HDL). Half of serum alpha-tocopherol resides in the HDL sub-fraction.55 Therefore, vitamin E levels are highly correlated with total serum lipids. Approximately 40% of ingested vitamin E gets absorbed, although the percentage is affected by the presence of PUFAs, which decrease absorption efficiency. Long chain dietary triglycerides enhance absorption. The different isomers are also absorbed with different efficiency.55

Iron supplements destroy vitamin E.  High intakes of vitamin A reduce the uptake of vitamin E, whereas high doses of vitamin E can impair the absorption of vitamin K.56 Higher levels of delta- and gamma-tocopherols have been detected in serum having lower levels of alpha-tocopherol, suggesting that absorption and/or release from body pools is influenced by the presence of other isomers.

Effect of Food Processing, Cooking and Storage
Due to oxidation, the vitamin E content of food decreases upon exposure to oxygen. This process is accelerated by heat and light. Therefore, various amounts of vitamin E are lost from food during cooking, processing and storage at room temperature. Although minimal, loss of vitamin E also occurs during freezing.55

Dietary Sources
Dietary sources include vegetable oils such as safflower, peanut and sunflower oils. Other sources include mayonnaise, margarine, broccoli, asparagus, apples, brown rice, bananas, strawberries, spinach, peas, broccoli, baked potatoes, whole milk, liver, shrimp, chicken, steak, egg yolk, fish, nuts, oatmeal, cornflakes and wheat germ.55

Antioxidant Defense:  Cancer and Disease Prevention
Inverse correlations between serum levels of vitamin E and the incidence of diseases such as arthritis, cancer, cataracts and age-related macular degeneration have been established. The risks of developing coronary diseases such as ischemic heart disease,19 atherosclerosis52 and angina pectoris53 were shown to be dramatically reduced in individuals with a high vitamin E status. Moreover, the ability of vitamin E and its derivatives to inhibit mutagenesis and chromosomal damage caused by radiation and chemical damage in in vitro studies has been demonstrated.43 Additionally, Vitamin E can moderate increases in lipid peroxidation resulting from heavy exercise.54

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