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Other common
name(s): none
Scientific/medical
name(s): alpha-tocopherol, tocopherols, tocotrienols
Description
Vitamin E is an essential nutrient the human body needs to
function normally. The term vitamin E actually represents a group of
substances, the most important (to the human body) being
alpha-tocopherol. The main sources of vitamin E in the diet are
vegetable oils (especially safflower oil, sunflower oil, and cottonseed
oil), green leafy vegetables, nuts, cereals, meats, egg yolks, wheat
germ, and whole wheat products. Vitamin E deficiency is rare and occurs
almost exclusively in people with an inherited or acquired condition
that impairs their ability to absorb this vitamin. Symptoms of vitamin
E deficiency include muscle weakness, visual problems (especially at
night), and a poor sense of balance. Over a long period, vitamin E
deficiency may progress to blindness, heart disease, and impaired
thinking. Supplements are usually only necessary or recommended for
people with vitamin E deficiency or a condition that puts them at risk
for this deficiency.
Overview
There is some evidence of the protective effects of vitamin E
against prostate, bladder, and colorectal cancer; however, more
research is needed. The consensus of most clinical studies is that
vitamin E supplements do not have any overall health benefit or any
beneficial effect on heart disease and cancer in general, and may even
lead to increased risk of heart failure. Available scientific evidence
does not support claims that vitamin E significantly affects the growth
of cancers that have already formed.
How is it promoted for use?
Some proponents claim vitamin E plays a role in protecting the
body against cancer by bolstering the immune system. Some also believe
the vitamin can increase the effectiveness of some chemotherapy drugs
and may reduce some side effects of chemotherapy and radiation therapy.
However, others believe high doses of vitamin E might interfere with
the effectiveness of radiation therapy and chemotherapy.
Proponents also claim that vitamin E supplements protect
against heart attacks by preventing a buildup of harmful cholesterol in
the blood. There are also claims that vitamin E eases the inflammation
associated with arthritis, speeds the healing of wounds in people who
have suffered burns or have had surgery, and slows the progress of
Parkinson's disease and Alzheimer's disease. Vitamin E is also used to
protect against the effects of pollution and overexposure to the sun
and to lessen the risk for cataracts.
What does it involve?
A balanced diet normally provides adequate amounts of vitamin
E for the body's needs, especially a diet low in fat and high in green
leafy vegetables and fiber from grains and cereals. The recommended
daily allowance (RDA) of vitamin E for adults is 15 milligrams per day
from food, with nineteen milligrams per day recommended for women who
are breast-feeding. Vitamin E is often measured as IU (International
Units); one milligram equals 1.5 IU. This recommendation was revised by
the National Academy of Science (NAS) in April 2000. It also set the
upper limit of intake from supplements at one thousand milligrams per
day (1,500 IU).
Vitamin E supplements are taken as capsules, with a typical
dose being four hundred IU per day.
What is the history behind it?
Since the 1940s, researchers and others have thought that
vitamin E might prevent heart disease. Researchers have observed that
people who have cancer often also have low levels of vitamin E in their
blood. More recently, several clinical trials have been completed (and
other are still in progress) comparing the risk of cancer among
volunteers randomly assigned to receive either vitamin E supplements or
a placebo.
What is the evidence?
Vitamin E is an antioxidant, a compound that blocks the action
of free radicals (activated oxygen molecules that can damage cells).
Most of the evidence for the preventive effects of antioxidants such as
vitamin E comes from animal studies and from observational
epidemiologic studies using surveys estimating how much vitamin E a
person consumes from food and supplements. However, the most reliable
studies on this issue are controlled clinical trials, such as a large
1994 study of antioxidant vitamins and cancer conducted by the National
Cancer Institute (NCI) and the National Public Health Institute of
Finland. The study was designed to find out whether antioxidant
vitamins in higher doses than the RDA (50 milligrams) could reduce the
incidence of lung cancer, other types of cancer, and other illnesses
among 29,000 male smokers. The study found no beneficial effect of
vitamin E supplements on lung cancer incidence. It found lower rates of
prostate and colorectal cancer among those who received vitamin E, but
higher rates of bladder, stomach, and other types of cancer.
The 2000 National Academy of Sciences report stated that there
is not enough evidence to support claims that taking high doses of
antioxidants (such as vitamins C and E, selenium, and beta carotene)
can prevent chronic diseases.
Individual clinical trials can sometimes provide misleading
results because of variation in research methods or random statistical
variation. Because of this possibility, , researchers often analyze the
combined data from many studies. This approach is called meta-analysis.
A meta-analysis published in 2005 combined data from nineteen clinical
trials that looked at vitamin E supplements. The results showed that
vitamin E supplements do not lower the risk of heart disease or of
cancer overall, and that people who received the placebo actually lived
slightly longer than those receiving the supplements.
Another large clinical trial published in 2005 also found no
risk reduction for heart disease or cancer overall. It even suggested
that heart failure was slightly more common among people taking vitamin
E. A 2007 review of 68 studies of antioxidant vitamin supplements found
that people taking vitamin E supplements had a shorter life expectancy
than those who did not take these supplements.
At least 2 more clinical trials of vitamin E for disease
prevention are still in progress. The Women’s Health Study
began in 1991 and is expected to be completed in 2009. The SELECT
(Selenium and Vitamin E Cancer Prevention Trial) is studying the effect
of vitamin E alone or in combination with selenium (an antioxidant
mineral; see also Selenium)
on prostate cancer risk. The SELECT was expected to conclude in 2013.
However, a preliminary analysis in 2008 showed no difference in
prostate cancer risk between the groups taking the vitamin E supplement
and the placebo, and the results suggested that vitamin E might even
have slightly increased the risk of developing prostate cancer. The
selenium supplement did not appear to be beneficial, either, and early
results suggested that it might slightly increase the risk of
developing diabetes. Because of these possible risks, the researchers
advised participants to stop taking the supplements, but follow-up
tests will continue for several years to learn more about long term
effects of the supplements.
Vitamin E has also been studied in clinical trials of people
who have had one cancer in order to see if it could prevent cancer
recurrence or formation of a second cancer. Clinical trials of people
with head and neck cancer found it did not reduce the risk of
recurrence or the risk of a second cancer.
Some scientists believe that taking high doses of antioxidant
vitamins may actually interfere with the effectiveness of radiation
therapy and some chemotherapy drugs. No studies have yet been done in
humans to test this theory. However, one animal study found that
vitamin E actually increased the effectiveness of the chemotherapy drug
5-FU against colon cancer in mice. Further studies are necessary to
find out whether the results apply to humans.
Are there any possible problems or complications?
This product is sold as a
dietary supplement in the United States. Unlike companies that produce
drugs (which must provide the FDA with results of detailed testing
showing their product is safe and effective before the drug is approved
for sale), the companies that make supplements do not have to show
evidence of safety or health benefits to the FDA before selling their
products. Supplement products without any reliable scientific evidence
of health benefits may still be sold as long as the companies selling
them do not claim the supplements can prevent, treat, or cure any
specific disease. Some such products may not contain the amount of the
herb or substance that is written on the label, and some may include
other substances (contaminants). Though the FDA has written new rules
to improve the quality of manufacturing processes for dietary
supplements and the accurate listing of supplement ingredients, these
rules do not take full effect until 2010. And, the new rules do not
address the safety of supplement ingredients or their effects on health
when proper manufacturing techniques are used.
Most such
supplements have not been tested to find out if they interact with
medicines, foods, or other herbs and supplements. Even though some
reports of interactions and harmful effects may be published, full
studies of interactions and effects are not often available. Because of
these limitations, any information on ill effects and interactions
below should be considered incomplete.
Vitamin E supplements found in multivitamins are generally
considered safe as long as the levels do not exceed the recommended
dietary allowance. However, doses of vitamin E supplements of more than
800 IU (533 milligrams) taken over a long time can cause nausea,
vomiting, stomach pain, and diarrhea. High doses of supplements may
also slow the way the body absorbs vitamins A, D, and K, and can result
in deficiencies of these vitamins. Megadoses of vitamin E supplements
are not advised for people who are taking blood-thinning medications,
such as warfarin, because the supplements might counteract the effects
of the drugs. People with cancer should talk to their doctor before
taking vitamin E or other vitamin supplements, especially while they
are undergoing chemotherapy or radiation therapy. Relying on this type
of treatment alone and avoiding or delaying conventional medical care
for cancer may have serious health consequences.
Additional Resources
More information from your American Cancer
Society
The following information on complementary and alternative
therapies may also be helpful to you. These materials may be found on
our Web site (www.cancer.org)
or ordered from our toll-free number (1-800-ACS-2345).
References
Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group.
The effect of vitamin E and beta carotene on the incidence of lung
cancer and other cancers in male smokers. N Engl J Med.
1994;330:1029-1035.
Bairati I, Meyer F, Gélinas M, Fortin A, Nabid A,
Brochet F, Mercier JP, Têtu B, Harel F, Mâsse B,
Vigneault E, Vass S, del Vecchio P, Roy J. A randomized trial of
antioxidant vitamins to prevent second primary cancers in head and neck
cancer patients. J Natl
Cancer Inst. 2005;97:481-488.
Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C.
Mortality in randomized trials of antioxidant supplements for primary
and secondary prevention: systematic review and meta-analysis. JAMA.
2007;297:842-857.
Byers T, Guerrero N. Epidemiologic evidence for vitamin C and
vitamin E in cancer prevention. Am
J Clin Nutr.1995;62:1385S-1392S.
HOPE-TOO: NCI comment on published results. National Cancer
Institute Web site.
http://www.cancer.gov/newscenter/pressreleases/Hope-Too. Posted March
15, 2005. Accessed June 6, 2008.
Institute of Medicine (US). Panel on Dietary Antioxidants and
Related Compounds. Dietary reference intakes for vitamin C, vitamin E,
selenium, and carotenoids : a report of the Panel on Dietary
Antioxidants and Related Compounds, Subcommittees on Upper Reference
Levels of Nutrients and of Interpretation and Use of Dietary Reference
Intakes, and the Standing Committee on the Scientific Evaluation of
Dietary Reference Intakes, Food and Nutrition Board, Institute of
Medicine. Washington, DC: National Academy Press; 2000.
Jacobs EJ, Henion AK, Briggs PJ, Connell CJ, McCullough ML,
Jonas CR, Rodriguez C, Calle EE, Thun MJ. Vitamin C and vitamin E
supplement use and bladder cancer mortality in a large cohort of US men
and women. Am J
Epidemiol. 2002;156:1002-1010.
Kaplan GE, Collins T. Vitamin E deficiency. E-medicine Web
site. http://www.emedicine.com/med/topic2383.htm. Updated July 19,
2006. Accessed June 6, 2008.
Lawenda BD, Kelly KM, Ladas EJ, Sagar SM, Vickers A, Blumberg
JB. Should supplemental antioxidant administration be avoided during
chemotherapy and radiation therapy? J Natl Cancer Inst.
2008;100:773-783.
Lonn E, Bosch J, Yusef S, Sheridan P, Pogue J, Arnold JM, Ross
C, Arnold A, Sleight P, Probstfield J, Dagenais GR; HOPE and HOPE-TOO
Trial Investigators. Effects of long-term vitamin E supplementation on
cardiovascular events and cancer: a randomized controlled trial. JAMA.
2005;293:1338-1347.
Miller ER 3rd, Pastor-Barriuso R, Dalal D, Reimersma RA, Appel
LJ. Meta-analysis: high-dosage vitamin E supplementation may increase
all-cause mortality. Ann
Intern Med. 2005;142:37-46. Epub 2004 Nov 10.
Dietary supplement fact sheet: vitamin E. Office of Dietary
Supplements Web site. http://ods.od.nih.gov/factsheets/vitamine.asp.
Updated January 23, 2007. Accessed June 6, 2008.
National Institutes for Health Press Release. Review of
Prostate Cancer Prevention Study Shows No Benefit for Use of Selenium
and Vitamin E Supplements. October 27, 2008. Available online at:
http://www.nih.gov/news/health/oct2008/nci-27.htm. Accessed October 29,
2008.
Vitamin E. Memorial Sloan-Kettering Cancer Center Web site.
http://www.mskcc.org/mskcc/html/69415.cfm. Updated March 4, 2008.
Accessed June 6, 2008.
Willett WC, Stampfer MJ. Clinical practice. What vitamins
should I be taking, doctor? N Engl J Med. 2001;345:1819-1824.
Note: This information may not cover
all possible claims, uses, actions, precautions, side effects or
interactions. It is not intended as medical advice, and should not be
relied upon as a substitute for consultation with your doctor, who is
familiar with your medical situation.
Last Medical Review: 11/01/2008
Last Revised: 11/01/2008
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