|Nutrition and Nutrients|
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Vitamin E, Tocopherols & Tocotrienols
Vitamin E is an activity concept, like Vitamin A and Vitamin D, rather than a single substance. Currently there are 8 naturally occurring and 8 synthetic Vitamin E substances available. Vitamin E is composed of four different tocopherols (α, γ, δ, and β) and four corresponding tocotrienols.
Vitamin E supplements usually contain only α-tocopherol, the most abundant and biologically active form of vitamin E. The most recent reference dietary intakes for vitamin E are based on α-tocopherol only, whereas previous dietary intake recommendations were based on all eight naturally occurring forms of vitamin E. The major food sources of vitamin E are vegetable and seed oils. α-Tocopherol is more abundant in sunflower and wheat germ oils; corn and soybean oils contain mostly γ-tocopherol.
Since alpha-tocopherol is the principle Vitamin E, its activity has been used to set dosages for the range of Vitamin E compounds. One international unit (IU) is equivalent to 1.0 mg of alpha-tocopherol. The RDA for Vitamin E was set at 8-10 mg (12-15 IU) per day for adults.
The requirement of Vitamin E increases with increased intake of fat. Vegetable oils contain Vitamin E, and increased consumption of them tends to be self-supplementing. A tenfold increase in intake is required to double the concentration of Vitamin E in the blood. There is no overt clinical syndrome which marks Vitamin E deficiency, although brain and spinal cord dysfunction has been recognized in patients with fat malabsorption. Difficulties walking, and eye movement abnormalities are typical of Vitamin E deficient brain disease. Any digestive disorder that reduces the absorption of fat, especially cystic fibrosis, pancreatic disease, and celiac disease, will reduce the absorption of Vitamin E and may lead to deficiency disease. The status of Vitamin E should be monitored in every patient with chronic diarrhea.
Vitamin E along with vitamin C in animal and human models have shown benefit in prevention of damage from heart ischemia-reperfusion. Results from the nurses’ health study of over 87,000 female nurses showed that women at high intakes of vitamin E (greater than 100 mg per day) had a 36% reduction of myocardial infarction compared with those in the lowest group consuming less than 6 mgs per day. Increased Vitamin E, especially in combination with other antioxidants, can reduce the damage done by normal and increased exposure to oxygen free radicals. This antioxidant protection may, over a lifetime be useful in retarding aging and decreasing tissue damage from a variety cases - from air pollution, blood cell and vessel disease, inflammatory diseases, carcinogens. Increased Vitamin E is recommended for anyone doing physical training with higher doses (800 -1200 mg/day) for vigorous or prolonged exertions. Studies have shown that doses in the range of 1800-3000 IU /day will increase Vitamin E concentration in platelets and decrease their tendency to clump together. Vitamin E supplementation in the range of 400 IU twice to three times a day doubles the blood levels of Vitamin E and is probably adequate for most indications. Doses up to 1200 IU/day seem to be well tolerated. The most common side effects of excess Vitamin E are nausea, flatulence or diarrhea, usually transient. Fatigue, muscle weakness, and headaches are occasionally reported.
Morris et al reported that a high intake of a mixture of vitamin E tocopherols from food sources rather than from supplements is associated with a reduced risk of Alzheimer's Disease. They suggested that the benefit is not due to α-tocopherol alone but to a combination of tocopherol with tocotrienols.
In their review, Ahsan et al stated:" Tocotrienols possess powerful neuroprotective, antioxidant, anti-cancer and cholesterol lowering properties that often differ from the properties of tocopherols. Micromolar amounts of tocotrienol suppress the activity of HMG-CoA reductase, the hepatic enzyme responsible for the synthesis of cholesterol. Tocotrienols are thought to have more potent antioxidant properties than α-tocopherol. The unsaturated side chain of tocotrienol allows for more efficient penetration into tissues that have saturated fatty layers such as the brain and liver. Experimental research examining the antioxidant, free radical scavenging, effects of tocopherol and tocotrienols have found that tocotrienols appear superior due to their better distribution in the lipid layers of the cell membrane… In addition, tocotrienol has been suggested to have an anti-thrombotic and anti-tumor effect indicating that tocotrienol may serve as an effective agent in the prevention and/or treatment of cardiovascular disease and cancer. The physiological activity of tocotrienol suggests it to be superior than a-tocopherol in many pathophysiological conditions. Hence, the role of tocotrienol in the prevention of cardiovascular disease and cancer may have significant clinical implications. Additional studies on its mechanism of action, as well as, long-term intervention studies from the pharmacological point-of-view are required to elucidate its function. "
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