Vitamin E is a fat soluble vitamin. It exists in eight different forms, four tocopherols and four tocotrienols. Both the tocopherols and tocotrienols occur in alpha, beta, gamma and delta forms, determined by the number of methyl groups on the chromanol ring. Each form has its own biological activity. The most active form of vitamin E is alpha-tocopherol. Supplemental vitamin E is in a form of alpha-tocopheryl acetate, a form of alpha-tocopherol that protects its ability to function as an antioxidant.
The primary roles of vitamin E is the maintenance of membrane integrity, where vitamin E prevents the oxidation of unsaturated fatty acids contained in the phospholipds of the membranes. Thus vitamin E is referred to as an antioxidant. Due to this property it can stop reactions involving free radicals thus protect cells against its harmful effects. Free radicals are by-products of energy metabolism and by damaging cells may contribute to the development of cardiovascular disease and cancer. Vitamin E should be taken with other antioxidant for example Coenzyme Q10 or vitamin C, so that one can act as reducing agent for the other. Experiments show that vitamin E taken alone can become a free radical itself.
Other roles of vitamin E include, tocotrienols ability to reduce plasma cholesterol concentrations. In addition vitamin E increases immune function, improves glucose tolerance, and helps in recovery from exercise.
There are several studies done with athletes and/or active people. Hartman et al showed that Vitamin E supplementation can reduce DNA damage in peripheral WBCs after exhaustive exercise. Another study Kanter et al proved that 1000 IU taken one week before exercise diminished LDL oxidation rate. Some studies reported decrease in physical performance when vitamin E deficiency exists. But the research is still inconclusive.
The richest sources of vitamin E are oils from plants. Oils high in alpha-tocopherol include:
Soybean and corn oils contain some alpha-tocopherol, but mostly are rich in gamma-tocopherol. Main sources of tocotrienols include legumes and cereal grains such as wheat, barley, rice and oats.
Other good food sources of vitamin E include:
- nut butters
- whole grain cereals
- some fruits
The RDA for vitamin E for adult male and female is 15 mg or 22.5 IU. Tolerable upper intake has been established at 1,000mg. High intakes have been associated with increased bleeding, nausea, diarrhea, flatulence, impaired blood coagulation, muscle weakness, fatigue, and double vision. In addition high intakes of vitamin E may interfere with beta-carotene absorption and/or its conversion to retionl, as well as impaired absorption of vitamin K.
Vitamin E deficiency is rare however it may occur in individuals with fat malabsorption disorders such as cystic fibrosis, with pancreatic lipase deficiency, and hepatobiliary system disorders such as chronic cholestasis with decreased bile production. In addition there are inherited disorders of fat metabolism, which include abetalipoproteinemia and isolated vitamin E deficiency or ataxia. Administration of vitamin E in high doses is required to treat the disorders. Signs of unabsorbed fat is a passage of greasy stools or chronic diarrhea. Vitamin E deficiency symptoms include skeletal muscle pain and weakness, ceroid pigment accumulation, hemolytic anemia, cerebellar ataxia, loss of vibratory sense, and loss of limb coordination.