Vitamin E

Vitamin E is a class of eight related fat-soluble organic compounds that the body needs to remain healthy. Humans cannot make vitamin E, so they must get it from foods in their diet. Alpha-tocopherol is the most biologically active form of vitamin E in humans, and vitamin E in dietary supplements is usually synthetic alpha-tocopherol.

The primary role of vitamin E in the human body appears to be as an antioxidant. Antioxidants help protect the body against damage caused by free radicals. Free radicals are formed during normal metabolic processes. Free radicals in the body increase with exposure to environmental toxins such as cigarette smoke, ultraviolet light, and radiation. Free radicals react with and damage compounds in the body, especially DNA (the genetic material) and fats (lipids) in cell membranes. Cellular damage from free radicals plays an important role in aging and in the development of some diseases, such as cancer and cardiovascular disease. Antioxidants react with free radicals to neutralize them and prevent cellular damage. As a fat-soluble compound, vitamin E is an important lipophilic antioxidant that helps prevent damage to the lipids in cell membranes.

The eight different but closely related compounds that comprise vitamin E are alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma-, and delta-tocotrienol. Each of these compounds has a different degree of activity in the human body, with alpha-tocopherol as the most active form. Vitamin E in dietary supplements is usually a synthetic alpha-tocopherol called dl-alpha-tocopheryl acetate.

The functions of vitamin E in the human body are not well understood. Vitamin E first came to public attention in the 1980s, as scientists began to understand the importance of free-radical damage in the early development of atherosclerosis (artery clogging), as well as vision loss, cancer, and other chronic conditions.

Vitamin E

The Institute of Medicine (IOM) of the U.S. National Academy of Sciences has developed dietary reference intake (DRI) values for vitamins and minerals. DRIs consist of three sets of numbers. The recommended dietary allowance (RDA) defines the average daily amount of a nutrient needed to meet the health needs of 97%–98% of the population. The adequate intake (AI) is an estimate set when there is not enough information to determine an RDA. The tolerable upper intake level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The values are defined in both milligrams (mg) per day and the international units (IU) per day used on dietary supplement labels; 1 mg of alpha-tocopherol equals about 1.5 IU. There are different forms of alpha-tocopherol. The AIs and RDAs are defined for only the form of alpha-tocopherol that occurs naturally in foods and that is used in fortified foods and supplements, although other forms of alpha-tocopherol are also used in fortified foods and supplements. The ULs apply to any form of alpha-tocopherol:

Although the ULs have been challenged as being set too high, it is also believed that the vast majority of adults who do not take supplemental vitamin E are not getting the RDA for vitamin E. However, it is possible to obtain adequate vitamin E by consuming vitamin E–rich or –enriched foods.

A balanced diet that is low in fats and high in green, leafy vegetables and fiber from grains and cereals will usually provide an adequate amount of vitamin E. However, vitamin E is found in only a limited number of foods. In addition to green, leafy vegetables, some oils—especially safflower, sunflower, and cottonseed oils—and nuts have vitamin E. Meats, egg yolks, wheat germ, and whole-wheat products also have vitamin E. Some breakfast cereals are fortified with vitamin E, as indicated on the label. In addition, the U.S. Food and Drug Administration requires that all foods containing olestra, a compound that reduces fat absorption, be fortified with the fat-soluble vitamins A, D, E, and K. However, the bioavailability of vitamin E (amount that is absorbed by the body) varies in different foods.

The approximate vitamin E (alpha-tocopherol) content for some common foods includes:

Multivitamins generally contain 30–60 IU or 20–40 mg of vitamin E. Vitamin E supplements typically contain 400–800 IU or 270–530 mg.

Most of the health benefits that are claimed for vitamin E are based on its antioxidant properties. However, controversy surrounds the use of vitamin E dietary supplements to help prevent or treat disease. Beginning as early as the 1940s, researchers suggested that vitamin E might protect against heart disease. Because vitamin E oxidizes LDL or “bad” cholesterol, researchers suggested that large doses might prevent or slow the build up of material on artery walls and thus help prevent cardiovascular disease. Initially it appeared that large doses of vitamin E might help prevent both heart disease and some cancers. Cardiologists began prescribing vitamin E supplements for their patients and taking the supplements themselves. When they began developing flu-like symptoms and realized they were experiencing toxic effects from the supplements, they cut back on the dose but continued taking vitamin E. Eventually, vitamin E studies began reporting mixed or contradictory effects. For example, a 2004 meta-analysis of 19 major clinical trials involving more than 136,000 individuals found that taking 400 IU or more of vitamin E daily increased the risk of death by about 4%. Other studies have indicated that high doses of vitamin E increase the risk of heart failure. The American Heart Association does not recommend the use of antioxidant supplements for preventing heart disease.

There are claims that vitamin E helps protect against cancer by strengthening the immune system and preventing damage to DNA and other cellular components. Researchers observed that cancer patients often have low blood levels of vitamin E. There are claims that vitamin E increases the effectiveness of some chemotherapy drugs and may reduce some side effects from chemotherapy and radiation therapy used to treat cancer. Others have argued that high doses of vitamin E interfere with the effectiveness of both radiation and chemotherapy. However, most studies have indicated that vitamin E supplements have no effect on the prevention or treatment of cancer. In fact, a 2011 follow-up of a clinical trial involving 35,000 men concluded that those who took vitamin E supplements were more likely to develop prostate cancer.

Studies of other health claims for vitamin E supplements have yielded equally contradictory results. These claims include easing inflammation from arthritis, speeding healing from burns or surgery, slowing the progression of Parkinson's and Alzheimer's diseases, preventing or treating cataracts and age-related macular degeneration, and protecting against the damaging effects of pollution and sun exposure. Although some of the confusion surrounding the effects of vitamin E supplements may stem from the many different forms of vitamin E and a lack of knowledge about the specific functions of these different forms, it is now generally accepted that vitamin E supplements are not beneficial and may be harmful. Supplements are usually only necessary or recommended for people with vitamin E deficiency or a condition that puts them at risk for a deficiency.

Vitamin E deficiency is almost as controversial as the purported benefits from vitamin E supplementation. Severe vitamin E deficiency damages nerves, especially those in the hands and feet. Deficiency can cause loss of balance and coordination and muscle weakness. It can also damage the retina of the eye, leading to vision loss. Over the long term, vitamin E deficiency may progress to blindness, heart disease, nerve damage, and impaired thinking.

True vitamin E deficiency is believed to be rare and to occur almost exclusively in people with an inherited or acquired condition that impairs their ability to absorb the vitamin. It is generally assumed that almost all healthy people in the developed world obtain enough vitamin E through their diet to prevent symptoms of vitamin E deficiency. However, although signs of vitamin E deficiency may develop quickly in children, symptoms can take years to become apparent in adults. Furthermore, there is some debate about the prevalence of subclinical vitamin E deficiency that does not cause obvious symptoms.

Those at greatest risk for vitamin E deficiency include:

Some experts believe that the UL for vitamin E in healthy adults of 1,500 IU daily is too high, especially since it is based on research done in the 1950s and since some studies have found that much lower daily amounts can increase the death rate. The recommended upper daily limit in the United Kingdom is 800 IU.

Antioxidant supplements can be harmful and are toxic at high doses. They can bind to minerals in the diet, preventing their absorption, and may increase the risk of lung cancer. Large doses of vitamin E increase the risk of bleeding. Vitamin E supplements should not be taken within one month of surgery because of this risk. People who are vitamin K-deficient, who have liver damage, or who have a history of bleeding ulcers should be wary of vitamin E supplements. Although the effects of vitamin E on chemotherapy drugs and radiation therapy are controversial, most oncologists advise their patients to avoid antioxidant vitamin and mineral supplements during treatment.

The vitamin E in multivitamins is generally considered to be safe, as long as it does not exceed the RDA. More than 800 IU or 533 mg taken daily over the long-term may cause nausea, vomiting, diarrhea, and stomach pain. Other uncommon side effects of vitamin E supplementation include damage to the retina, breast soreness, fatigue, emotional disturbances, and thyroid hormone disturbances. High doses of vitamin E may slow the absorption of vitamins A, D, and K, leading to deficiencies. Vitamin E supplements may also cause heart problems or interfere with blood clotting.

Large doses of vitamin E increase the chance of bleeding. People who are taking blood-thinning medications such as warfarin (Coumadin), heparin, or clopidogrel (Plavix), or aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen, are advised against taking large doses of vitamin E.

Many other drugs may interact with vitamin E including:

No complications are expected when vitamin E is used in the recommended amounts.

See also Adolescent nutrition ; Antioxidants ; Artificial preservatives ; Dietary supplements ; Omega-3 and omega-6 fatty acids ; Phytonutrients ; Vitamins ; Whole grains .