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Editor's note: A recent study found that use of
vitamin E supplements was not associated with reduced risk of lung cancer among
the general population. Among current smokers, taking vitamin E supplements may
even dramatically increase the risk of the cancer up to 28%. The
following is compiled by a foodconsumer.org editor for those who want to know
more about this vitamin. The key point is that vitamin E by definition is essential
to your health and you should not avoid it. The best source is of course food.
But when you take a supplement, make sure you are taking the natural form of
vitamin E. Read on for detail.
Vitamin E: What you need to know
What is vitamin E?
Vitamin E is a group of eight nutrients including four tocopherols, (alpha-, beta-, gamma- and delta-) and four tocotrienols (alpha-, beta-, gamma- and delta-). Alpha-tocopherol is the only form of vitamin E that is active in the body.
What does vitamin E do in the body?
The form of vitamin E most known today is alpha-tocopherol, which is believed to be used in the body mainly as an antioxidant. Antioxidants are expected to neutralize free radials endogenously and oxidative environmental pollutants.
Alpha-tocopherol is fat-soluble and helps protect against oxidation of fatty components in the cell membrane and also protect fats in low density liporpoteins (LDLs), which transport cholesterol from the liver to the tissue of the body. Oxidation of LDLs could lead to development of cardiovascular diseases.
Alpha-tocopherol also affects some enzymes and the production of immune and inflammatory cells among other things.
The functions of other forms of vitamin E are not as well understood.
What are the consequences of vitamin E deficiency?
Vitamin E deficiency could be caused either by low intake of the vitamin or by some conditions that disable the alpha-tocopherol transfer protein or by some problem with fat absorption. Those who can't absorb fat such as patients with cystic fibrosis or cholesterol liver disease would have a problem with absorbing this vitamin from the diet, potentially leading to vitamin E deficiency.
The main consequences of severe vitamin E deficiency are neurological symptoms such as ataxia (impaired balance and coordination), peripheral neuropathy (injury to sensory nerves, myopathy (muscle weakness) and pigmented retinopathy (damage to the eye retina). People who experience these symptoms should be checked for their vitamin E status. Children are more sensitive and thus more vulnerable to vitamin E deficiency and they can quickly show neurological symptoms while adults may not develop symptoms due to the deficiency for 10 to 20 years.
Vitamin E deficiency due to low intake of this nutrient rarely results in any reported symptoms. In effect, vitamin E deficiency due to low dietary intake is rare although suboptimal intake of this nutrient is found common in the U.S. population. A study known as the U.S. National Health and Nutrition Examination Survey III (NHANES III) showed 27 % of whites, 41% of blacks, 28% Mexican Americans and 32% of others have less than 20 micromoles/liter, a level of vitamin E that is believed to pose a risk for cardiovascular disease.
What is the recommended dietary allowance for vitamin E?
The RDA set by the Food and Nutrition Board of the Institute of Medicine in 2000 varies with age. The RDA for both adult males and females is 15 mg or 22.5 IU per day. Pregnancy does not require extra vitamin E, but breastfeeding mother need 19 mg or 28.5 IU per day.
What are the conditions or diseases on which vitamin E may have an effect?
Observational studies have showed an association between increased vitamin E intake and decreased risk of myocardial infarction or heart attack or death from heart disease in both men and women. Studies also found plasma levels of alpha-tocopherol were inversely linked to the severity of carotid atherosclerosis. But trials often failed to see any protective effect of this vitamin on heart attacks and death.
Observational studies also showed vitamin E may protect against cataracts, but interventional trials did not find any protective effect when 400 IU of vitamin E was used for 7 years.
Alpha-tocopherol was also found to boost the immune response. One study showed 200 mg of synthetic-tocopherol daily for a few months increased production of antibodies in response to hepatitis B vaccine and tetanus vaccine in elderly people.
Because free radials are believed to cause damage to DNA, neutralization of these compounds by antioxidant vitamins such as vitamin E is believed to have a preventative effect against cancer. But many studies showed that vitamin E supplements were not linked to reduced risk of cancer. In a recent study, vitamin E supplementation for ten years was found even to increase the risk of lung cancer in current smokers.
What are the foods that contain high levels of vitamin E?
The major dietary sources of alpha-tocopherol include vegetable oils such as olive, sunflower and safflower oils; nuts such as almonds, hazelnuts and peanuts; whole grains products; and green leafy vegetables such as spinach. All eight forms of vitamin E occur naturally in foods.
Those who would use vitamin E supplements should check and see if the form they buy is natural or synthetic. They may better off buying and using only the natural form. The synthetic form of vitamin is biochemically not usable by the body and potentially cause a physiologic problem in the body. The natural form in food (not the fortified) is the form of the isomer,
RRR-alpha-tocopherol. In supplemental vitamin E,
all-rac-alpha-tocopherol means the vitamin is synthetic.
There are some other forms of vitamin E or derivatives used in supplements. Foodconsumer.org recommends use of the natural form
What are the possible side effects of vitamin E?
Vitamin E is fat-soluble and too much of its intake through supplements may cause some side effects. But the Food and Nutrition Board of the Institute of Medicine believes 1000 mg or 1500 IU of alpha-tocopherol per day can be tolerated by adults aged 19 or older. The dietary intake of this vitamin rarely poses any risk.
© 2004-2008 by foodconsumer.org unless otherwise specified
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