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Vitamin
E
[Vitamin
E: What is it? | What foods provide Vitamin E?]
[Recommended Dietary Allowance]
[When can vitamin E deficiency occur?]
[Who may need extra vitamin E to prevent a deficiency]
[Issues and controversies | Too
much vitamin E]
[Selected food sources of vitamin E |
References]
Vitamin
E: What is it?
Antioxidants such as vitamin E act to protect your cells against the
effects of free radicals, which are potentially damaging by-products of
the body's metabolism. Free radicals can cause cell damage that may
contribute to the development of cardiovascular disease and cancer.
Studies are underway to determine whether vitamin E might help prevent or
delay the development of those chronic diseases2,3.
Vitamin E is a
fat-soluble vitamin that exists in eight different forms. Each form has
its own biological activity, the measure of potency or functional use in
the body1. Alpha-tocopherol is
the most active form of vitamin E in humans, and is a powerful biological
antioxidant2,3.
What
foods provide vitamin E?
Vegetable oils, nuts, and green leafy vegetables are the main dietary
sources of vitamin E. Fortified cereals are also an important source of
vitamin E in the United States. The table of selected food sources of
vitamin E suggests foods that contain vitamin E4.
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What is
the Recommended Dietary Allowance for vitamin E for adults?
The Recommended Dietary Allowance (RDA) is the average daily dietary
intake level that is sufficient to meet the nutrient requirements of
nearly all (97-98%) healthy individuals in each life-stage and gender
group5. The 2000 RDAs for vitamin E5
for adults, in milligrams (mg) and International Units (IUs) are:
|
Life-Stage
|
Men and
Women
|
Pregnancy
|
Lactation
|
|
Ages 19+
|
15 mg* or 22
IU
|
|
|
|
All ages
|
|
15 mg*
or 22 IU
|
19 mg*
or 28 IU
|
|
*1
mg alpha-tocopherol equivalents = 1.5 IU
|
The RDA for vitamin
E is based on the alpha-tocopherol form because it is the most active,
or usable, form5, 6. Unlike
other vitamins, the form of alpha-tocopherol made in the laboratory and
found in supplements is not identical to the natural form, and is not
quite as active as the natural form.
Results of two
national surveys, the National Health and Nutrition Examination Survey (NHANES
III 1988-91) and the Continuing Survey of Food Intakes of Individuals
(1994 CSFII) indicated that the dietary intake of most Americans does not
provide the recommended intake for vitamin E. However, a 2000 Institute of
Medicine (IOM) report on vitamin E states that intake estimates of vitamin
E may be low because energy and fat intake is often underreported in
national surveys and because the kind and amount of fat added during
cooking is often not known5. The IOM states that most North
American adults get enough vitamin E from their normal diets to meet
current recommendations5. However, they do caution individuals
who consume low fat diets because vegetable oils are such a good dietary
source of vitamin E. "Low-fat diets can substantially decrease
vitamin E intakes if food choices are not carefully made to enhance alpha-tocopherol
intakes"5.
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When
can vitamin E deficiency occur?
Vitamin E deficiency is rare in humans. There
are three specific situations when a vitamin E deficiency is likely to
occur. Vitamin E deficiency is seen in persons who cannot absorb dietary
fat, has been found in premature, very low birth weight infants (birth
weights less than 1500 grams, or 3 1/2 pounds)3,6,
and is seen in individuals with rare disorders of fat metabolism9.
A vitamin E deficiency is usually characterized by neurological problems
due to poor nerve conduction.
Who
may need extra vitamin E to prevent a deficiency?
Individuals who cannot absorb fat may require a vitamin E supplement because
some dietary fat is needed for the absorption of vitamin E from the gastrointestinal
tract. Anyone diagnosed with cystic fibrosis, individuals who have had
part or all of their stomach removed, and individuals with malabsorptive
problems such as Crohn's disease may not absorb fat and should discuss
the need for supplemental vitamin E with their physician3.
People who cannot absorb fat often pass greasy stools or have chronic
diarrhea.
Very low birth
weight infants may be deficient in vitamin E3,
6. These infants are usually under
the care of a neonatologist, a pediatrician specializing in the care of
newborns, who evaluates and treats the exact nutritional needs of
premature infants.
Abetalipoproteinemia
is a rare inherited disorder of fat metabolism that results in poor
absorption of dietary fat and vitamin E9.
The vitamin E deficiency associated with this disease causes problems such
as poor transmission of nerve impulses, muscle weakness, and degeneration
of the retina that can cause blindness10.
Individuals with abetalipoproteinemia may be prescribed special vitamin E
supplements by a physician to treat this disorder.
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What
are some current issues and controversies about vitamin E? [Heart
disease | Cancer | Cataracts]
[Vitamin E Update: Gamma-tocopherol, Not Alpha-tocopherol, Inhibits
Cancer Cell Growth]
[Vitamin
E May Reduce Risk of Parkinson's]
Vitamin
E and heart disease
Preliminary research has led to a widely held belief that vitamin E may
help prevent or delay coronary heart disease
11. Researchers are fairly
certain that oxidative modification of LDL-cholesterol (sometimes called
"bad" cholesterol) promotes blockages in coronary arteries
that may lead to atherosclerosis and heart attacks. Vitamin E may help
prevent or delay coronary heart disease by limiting the oxidation of
LDL-cholesterol12. Vitamin E
also may help prevent the formation of blood clots, which could lead to
a heart attack. Observational studies have associated lower rates of
heart disease with higher vitamin E intake. A study of approximately
90,000 nurses suggested that the incidence of heart disease was 30% to
40% lower among nurses with the highest intake of vitamin E from diet
and supplements. The range of intakes from both diet and supplements in
this group was 21.6 to 1,000 IU (32 to 1,500 mg), with the median intake
being 208 IU (139 mg)13. A
1994 review of 5,133 Finnish men and women aged 30 - 69 years suggested
that increased dietary intake of vitamin E was associated with decreased
mortality (death) from heart disease14.
But even though these observations are promising, randomized clinical
trials raise questions about the role of vitamin E supplements in heart
disease. The Heart Outcomes Prevention Evaluation (HOPE) Study followed
almost 10,000 patients for 4.5 years who were at high risk for heart
attack or stroke15. In this
intervention study the subjects who received 265 mg (400) IU of vitamin
E daily did not experience significantly fewer cardiovascular events or
hospitalizations for heart failure or chest pain when compared to those
who received a sugar pill. The researchers suggested that it is unlikely
that the vitamin E supplement provided any protection against
cardiovascular disease in the HOPE study. This study is continuing, to
determine whether a longer duration of intervention with vitamin E
supplements will provide any protection against cardiovascular disease5.
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Vitamin
E and cancer
Antioxidants such as vitamin E help protect against the damaging effects
of free radicals, which may contribute to the development of chronic
diseases such as cancer 5.
Vitamin E also may block the formation of nitrosamines, which are
carcinogens formed in the stomach from nitrites consumed in the diet.
Vitamin E also may protect against the development of cancers by
enhancing immune function16.
Unfortunately, human trials and surveys that tried to associate vitamin
E with incidence of cancer have been generally inconclusive.
Some evidence
associates higher intake of vitamin E with a decreased incidence of
prostate cancer and breast cancer17.
There is evidence that vitamin E may reduce the size of cysts in women
with fibrocystic breast disease, which is a risk factor for breast
cancer. However, an examination of the effect of dietary factors,
including vitamin E, on incidence of postmenopausal breast cancer in
over 18,000 women from New York State did not associate a greater
vitamin E intake with a reduced risk of developing breast cancer18.
A study of women
in Iowa provided evidence that an increased dietary intake of vitamin E
may decrease the risk of colon cancer, especially in women under 65
years of age19. On the other
hand, vitamin E intake was not statistically associated with risk of
colon cancer in almost 2,000 adults with cancer who were compared to
controls without cancer20. At
this time there is limited evidence to recommend vitamin E supplements
for the prevention of cancer.
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Vitamin
E and cataracts
Cataracts
are growths on the lens of the eye that cloud vision. They increase the
risk of disability and blindness in aging adults. Antioxidants are being
studied to determine whether they can help prevent or delay cataract
growth. Observational studies have found that lens clarity, which is
used to diagnose cataracts, was better in regular users of vitamin E
supplements and in persons with higher blood levels of vitamin E21.
A study of middle aged male smokers, however, did not demonstrate any
effect from vitamin E supplements on the incidence of cataract formation22.
The effects of smoking, a major risk factor for developing cataracts,
may have overridden any potential benefit from the vitamin E, but the
conflicting results also indicate a need for further studies before
researchers can confidently recommend extra vitamin E for the prevention
of cataracts.
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What
is the health risk of too much vitamin E?
The health risk of too much vitamin E is low23.
A recent review of the safety of vitamin E in the elderly indicated that
taking vitamin E supplements for up to four months at doses of 530 mg or
800 IU (35 times the current RDA) had no significant effect on general
health, body weight, levels of body proteins, lipid levels, liver or
kidney function, thyroid hormones, amount or kinds of blood cells, and
bleeding time24. Even though
this study provides evidence that taking a vitamin E supplement containing
530 mg or 800 IU for four months is safe, the long term safety of vitamin
E supplementation has not been tested. The Institute of Medicine has set
an upper tolerable intake level for vitamin E at 1,000 mg (1,500 IU) for
any form of supplementary alpha-tocopherol per day because the nutrient
can act as an anticoagulant and increase the risk of bleeding problems.
Upper tolerable intake levels "represent the maximum intake of a
nutrient that is likely to pose no risk of adverse health effects in
almost all individuals in the general population"5.
This fact sheet was developed
by the Clinical Nutrition Service, Warren Grant Magnuson Clinical Center,
National Institutes of Health (NIH), Bethesda, MD, in conjunction with the
Office of Dietary Supplements (ODS) in the Office of the Director of NIH.
The mission of ODS is to strengthen knowledge and understanding of dietary
supplements by evaluating scientific information, stimulating and supporting
research, disseminating research results, and educating the public to foster
an enhanced quality of life and health for the U.S. population. The Clinical
Nutrition Service and the ODS would like to thank the expert scientific
reviewers for their role in ensuring the scientific accuracy of the information
discussed in this fact sheet.Updated 12/2000
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