VITAMIN E
Vitamin E is the collective name for a group of fat-soluble compounds with distinctive antioxidant activities. Naturally occurring, vitamin E exists in eight forms -(alpha-, beta-, gamma- and delta-tocopherol and alpha-, beta-, gamma-,and delta-tocotrienol.
The varying forms have varying levels of biological activity.
Gamma-tocopherol is the most common form in the American diet, found in corn oil, sunflower oil and safflower oil. Alpha- tocopherol is the second most common, found in wheat germ oil, sunflower & salflower oils, and is the most biologically active form and the form recognized to meet human requirements.
Serum concentrations of vitamin E (alpha-tocepherol) depend on the liver, which takes up the nutrient after the various forms are absorbed from the small intestine. The liver metabolizes and excretes the other vitamin E forms. The liver returns only alpha-tocopherol. (Thus there is less of the other forms of vitamin E in the blood and cells and therefore there has been less research of the other forms.)
Vitamin E has been proposed for the prevention or treatment of numerous health conditions, often based on its antioxidant properties.
Antioxidants protect cells from the damaging effects of free radicals, which are molecules that contain an unshared electron. Free radicals damage cells. Unshared electrons are highly energetic and react rapidly with oxygen to form reactive oxygen species (ROS). The body forms ROS when it converts food to energy and antioxidants might protect cells from damaging effects of ROSs. (Vitamin E is a fat-soluble antioxidant that stops the production of ROS formed when fat undergoes oxidation. ) The body is also exposed to free radicals from air pollution and ultraviolet radiation from the sun.
The antioxidant function is considered to be the most important function of vitamin E and the one it is best known for. However the importance of the antioxidant properties of this molecule at the concentrations present in the body are not clear and it is possible that the reason it is required in the diet is unrelated to its ability to act as an antioxidant.
Other functions of vitamin E are: a regulatory effect on enzymatic activities, effect on gene expression, effect on the connective tissue growth factor, repair of the wounds and regeneration of the extra cellular tissue lost or damaged during atherosclerosis, a role in neurological functions, and inhibition of platelet aggregation. It is a signaling molecule, may protect neurons from damage and may help in cholesterol reduction.
Vitamin E is also involved in immune function, cell signaling (the transfer of information from one cell to another or across different structures inside a cell), and regulation of metabolic processes. Vitamin E inhibits an enzyme involved in cell proliferation and differentiation in smooth muscle cells and platelets. It increases the expression of two enzymes that dilates blood vessels and inhibits platelet aggregation.
Vitamin E is found naturally in:
Wheat germ, sunflower oil, safflower oil
Nuts and nut oils, like almonds and hazelnuts
Green leafy vegetables like lettuce, spinach, turnip, beet, collard and dandelion greens
Tomato products
Pumpkin
Sweet potato
Mangoes
Asparagus
Broccoli
Eggs
Fortified cereals
Fruit, meat, nuts, vegetable oils – corn, cottonseed, soybean, olive oil,
Wheat germ
Whole grains.
(Cooking and storage may destroy some of the Vitamin E.)
Most individuals in the U.S. are believed to obtain sufficient vitamin E from dietary sources.
Vitamin E deficiency is rare. It may occur in people with diminished fat absorption in the intestine, The digestive track requires fat to absorb Vitamin E and people with fat-metabolism disorders are more likely to become deficient. Thus it can be found in Chrohn’s disease, cystic fibrosis, malnutrition, very-low-fat diets, after surgery and in infants taking unfortified formulas. Supplementation for deficiency should be under the care of a physician and nutritionist.
The recommended dietary allowance (RDA) obtained through food consumption is considered to be safe and beneficial. Recommended dietary allowances (RDSs) for Vitamin E are provided in alpha-tocopherol equivalents (ATEs) to account for the different biological activities of the various forms of Vitamin E., as well as in international units (IU) which food and supplement labels often use.
Conversion: one milligram of an ATE = 1.5 IU.
The RDA for adults older that 14 years is 15 milligrams (or 22.5 IU).
Pregnant women, any age, it is 15 milligrams ( or 22.5 IU) and for breastfeeding women of any age it is 19 milligrams ( or 28.5 IU.)
To convert from mg to IU: 1 mg = 1.5 IU of natural form or 2.22 of the synthetic form
To convert from IU to mg: 1 IU = .67 mg or the natural form and .45 mg of the synthetic form.
Research has not found any adverse effects from consuming Vitamin E in food.
For adults 18+ years, there are tolerable upper limits of dosing for supplementary alpha-tocopherol recommended by the U.S. Institute of Medicine which is 1000 milligrams daily (equivalent to 1,500 IU).
The Upper Limits apply to all forms of supplemental alpha-tocopherol. Doses of up to 1000 mg/day (1500 IU) of the natural form or 1,100 IU /day of the synthetic form in adults appear to be safe.
Vitamin E can be obtained as a supplement in natural or synthetic form. Natural forms are usually labeled “d” and synthetic forms labeled “dl”
Supplements of vitamin E usually provide only alpha-tocopherol, although “mixed” products contain other tocopherols. Naturally occuring alpha-tocopherol exists in one sterosometric form. In contrast, synthetically produced alpha-tocopherol contains equal amounts of its 8 steroisomers.
The synthetic vitamin E is only half as active as the same amount of the natural form.
Many claims have been made about Vitamin E’s potential to promote health and prevent and treat disease. The mechanisms by which Vitamin E might do this include its function as an antioxidant and its roles in anti-inflammatory processes, inhibition of platelet aggregation and immune enhancement. Current evidence, however does not indicate any positive effects for treatment in such medical conditions. Results often show no effect or a negative effect or are controversial. There are many promotions suggesting help in several conditions such as heart, cancer and aging. These are of interest with the following considerations.
-Coronary heart disease – Evidence that Vitamin E could help prevent or delay coronary heart disease (CHD) comes from several sources – studies have found that vitamin E inhibits oxidation of low-density lipoprotein (LDL) cholesterol and it may help prevent the formation of blood clots that could lead to a heart attack. To date, there has been no evidence that vitamin E prevents or helps in the treatment of cardiovascular disease.
Cancer – Vitamin E might protect the cells from the damaging effects of free radicals. It may also block the formation of carcinogenic nitrosamines, formed in the stomach from nitrites in foods and protect against cancer by enhancing immune function . Unfortunately human trials and research that have attempted to associate Vitamin E intake have found that Vitamin E is not beneficial. Evidence is insufficient to support taking Vitamin E to prevent cancer.
Cognitive decline – Most research results do not support the use of Vitamin E supplements to maintain cognitive performance or slow its normal decline with normal aging.
Also often mentioned as potential conditions in which Vitamin E may help are: acne, air pollution protection, allergies, anti-aging, athletic performance, childhood growth, heart failure, diabetic foot ulcers, eye disorders, hair loss, hypertension, skin aging, etc. These conditions are very serious and should be evaluated by a physician.
More research must be done to support the use of Vitamin E supplements to aid in treatment or to slow or prevent disease. There is a lack of clearly proven medical uses of Vitamin E supplementation beyond the recommended daily allowance. There is ongoing research in many diseases, especially cancer and heart disease.
Concerns, however, have been raised about the safety of vitamin E supplementation, especially in high doses. High doses of supplements have been found to cause hemorrhage and interrupt blood coagulation in animals and clinical trials have found an increased risk of hemorrhagic stroke in participants and possible increased bleeding in patients taking blood-thinning agents. Some evidence suggests that use of regular high supplementation may increase the risk of death from all causes by a small amount.
Interaction with medications – Vitamin E can inhibit platelet aggregation and antagonize vitamin K-dependent clotting factors. Taking Vitamin E with other antioxidants, such as vitamin C, selenium, and beta-carotene has slowed the rise of high-density lipoprotein (HDL) cholesterol levels.
Oncologists usually advise against the use of antioxidant supplements during cancer chemotherapy or radiotherapy because they might reduce the effectiveness of these therapies by inhibiting cellular damage in cancerous cells.
Some evidence suggests that long-term use of daily supplementation with 400 IU or greater daily may have adverse health effects. Although controversial, long-term supplementation should be approached cautiously until there is further evidence. Skin reaction or allergy has been reported with topical vitamin E preparations, such as ointments or vitamin E-containing deodorants.
For short periods of time, vitamin E supplementation is generally considered safe at doses up to the recommended tolerable upper intake level. Chronic use of vitamin E should be used cautiously and high-dose vitamin E should be avoided.*
*Reference sources: Mayo Clinic, National Institute of Health, and Wikipedia.
