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Other common
name(s): B vitamins; vitamins B1, B2, B3, B5, B6, B7, B9,
and B12
Scientific/medical
name(s): thiamine (B1), riboflavin (B2), niacin (B3),
pantothenic acid (B5), pyridoxine (B6), biotin (B7), folic acid or
folate (B9), cobalamin (B12)
Description
B vitamins are essential nutrients for growth, development,
and a variety of other bodily functions. They play a major role in the
activities of enzymes, proteins that regulate chemical reactions in the
body, which are important in turning food into energy and other needed
substances. B vitamins are found in a variety of plant and animal food
sources.
Overview
B vitamins are an important part of the diet and are needed to
help avoid many health conditions. However, with the exception of
vitamin B9 (folic acid), there is not enough scientific evidence to
know whether B vitamins can reduce the risk of cancer. People with low
intake of folic acid are at increased risk for certain types of cancer.
A diet rich in vegetables containing this vitamin, and perhaps a daily
multivitamin supplement containing the recommended daily value of
vitamin B9 is recommended by some experts in cancer prevention (see Folic Acid).
Available scientific evidence does not support claims that any B
vitamin is an effective treatment for people who already have cancer.
How is it promoted for use?
Scientists know that B vitamins influence several important
bodily functions:
- Vitamin B1 (thiamin) and vitamin B2 (riboflavin) help the
body produce energy and affect enzymes that influence the muscles,
nerves, and heart.
- Vitamin B3 (niacin) has a role in energy production in
cells and in maintaining the health of the skin, nervous system, and
digestive system.
- Vitamin B5 (pantothenic acid) influences normal growth and
development.
- Vitamin B6 (pyridoxine) helps the body break down protein
and helps maintain the health of red blood cells, the nervous system,
and parts of the immune system.
- Vitamin B7 (biotin) helps break down protein and
carbohydrates and helps the body make hormones.
- Vitamin B9 (folic acid) helps the cells in the body make
and maintain DNA and is important in the production of red blood cells.
- Vitamin B12 (cobalamin) plays a role in the body's growth
and development. It also has a part in producing blood cells, the
functions of the nervous system, and how the body uses folic acid and
carbohydrates.
Deficiency of certain B vitamins can cause anemia, tiredness,
loss of appetite, abdominal pain, depression, numbness and tingling in
the arms and legs, muscle cramps, respiratory infections, hair loss,
eczema, poor growth in children, and birth defects in the fetuses of
pregnant women.
Women who are pregnant or breast-feeding require more folic
acid than others. The Public Health Service recommends that women of
childbearing age who can become pregnant should consume at least 400
micrograms of folic acid daily through dietary supplements and
fortified foods, in addition to a diet containing folate-rich foods, to
help prevent certain birth defects in their children.
Some alternative medical practitioners claim that deficiencies
in B vitamins weaken the immune system and make the body vulnerable to
cancer. They recommend high doses of B vitamins as treatments for
people with cancer. Many researchers are studying the relationships
between vitamin intake and risk of developing certain cancers.
What does it involve?
Nutritionists maintain that a balanced diet that includes 5
daily servings of fruits and vegetables, as well as grains, is
sufficient to provide most people with all the B vitamins they need.
Only small amounts of these vitamins are needed to reach the
recommended dietary intakes. Unfortunately, many people may not eat
enough fruits, vegetables, or other healthy foods to get the
recommended amounts. The National Academies of Science (NAS) recommends
that adults over the age of 50 take B vitamin supplements, or eat foods
enriched with these vitamins, in order to prevent deficiency, which is
common in this age group.
Vitamins B1 and B2 are found in cereals and whole grains. B1
is also found in potatoes, pork, seafood, liver, and kidney beans. B2
is found in enriched bread, dairy products, liver, and green leafy
vegetables. Vitamin B3 is found in liver, fish, chicken, lean red meat,
nuts, whole grains, and dried beans. Vitamin B5 is found in almost all
foods. Fish, liver, pork, chicken, potatoes, wheat germ, bananas, and
dried beans are good sources of vitamin B6. Vitamin B7 is manufactured
by intestinal bacteria and is also present in peanuts, liver, egg
yolks, bananas, mushrooms, watermelon, and grapefruit. Green leafy
vegetables, liver, citrus fruits, mushrooms, nuts, peas, dried beans,
and wheat bread contain vitamin B9. Vitamin B12 is found in eggs, meat,
poultry, shellfish, milk, and milk products.
Supplements that contain several B vitamins, usually in
combination with other nutrients, are sold in grocery stores, health
food stores, and over the Internet in pill form. Dosages vary by
manufacturer.
What is the history behind it?
While diseases due to vitamin deficiencies have been known for
centuries, just about all of the B vitamins were discovered in the
early 1900s. Since then, B vitamins have been studied to determine how
they affect the human body. As their importance and functions were
clarified, the U.S. government began recommending daily intake levels
to promote and maintain good health. The current recommended levels are
known as dietary reference intakes (DRIs). Research on the possible
role of some B vitamins in preventing cancer began in the last few
decades.
What is the evidence?
The limited data concerning B vitamins and cancer come mainly
from animal studies and from observational epidemiologic studies. These
types of studies are not as strong as randomized controlled clinical
trials and therefore must be interpreted with caution.
There is some evidence from observational epidemiologic
studies that increased intake of vitamin B9 (folic acid) is linked to a
lower risk of colon cancer, especially in people who are vitamin
deficient, such as those who drink excessive amounts of alcohol.
Evidence of effects on other types of cancer has been mixed.
Some (but not all) population studies have also shown a
possible link between intake of vitamin B6 and lower risks of
colorectal and breast cancers in women. Possible links between other B
vitamins and cancer risk have not been studied as extensively or have
been studied with mixed results.
While the results of studies on vitamin B6 and folate are
early and are not conclusive, they deserve further research. It is
still unclear whether taking in more B vitamins will help protect
against cancer or how much might be needed to reduce cancer risk.
Even if some B vitamins prove to be helpful in preventing
certain cancers, it does not necessarily follow that B vitamins would
be useful in treating cancers. In fact, some experts have cautioned
that certain B vitamins, such as thiamine and folic acid, might
actually make it easier for established tumors to grow. This is not
well proven, but caution is advised when considering taking large doses
of these vitamins.
At this time, it is hard to say how each nutrient or nutrient
combination affects a person’s risk of cancer. On the other
hand, studies of large groups of people have shown that those whose
diets are high in vegetables and low in animal fat, meat, and/or
calories have lower risks for some of the most common types of cancer.
Until more is known about this, the American Cancer Society recommends
eating a variety of healthful foods--with most of them coming from
plant sources--rather than relying on supplements.
While it is best to get vitamins and minerals from foods,
supplements may be helpful for some people. If a supplement is taken,
the best choice for most people is a balanced multivitamin/mineral
supplement that contains no more than 100% of the "Daily Value" of most
nutrients. Pregnant women, women of childbearing age, and people with
restricted food intakes should speak with their doctors about
supplements containing higher levels of certain vitamins.
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.
B vitamins are water-soluble, meaning that any excess intake
is largely excreted in the urine. Supplements containing B vitamins are
generally thought to be safe but still should not be taken in very
large doses. Possible side effects include gout, high blood sugar
levels, and skin problems. Overdoses can lead to heart and liver
problems. Rarely, large doses of vitamin B3 (niacin) supplements can
cause blurred vision, nausea, vomiting, and can make stomach ulcers
worse. High doses of folic acid supplements may interfere with at least
one chemotherapy drug, methotrexate, and similar medicines. Always tell
your doctor and pharmacist about any supplements and herbs you are
taking.
Relying on the use of B vitamins 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
Boros LG, Brandes JL, Lee WN, Cascante M, Puigjaner J, Revesz
E, Bray TM, Schirmer WJ, Melvin WS. Thiamine supplementation to cancer
patients: A double edged sword. Anticancer
Res. 1998;18:595-602.
Centers for Disease Control and Prevention. Folate status in
women of childbearing age, by race/ethnicity--United States, 1999-2000,
2001-2002, and 2003-2004. MMWR
Morb Mortal Wkly Rep. 2007;55:1377-1380.
Food and Nutrition Board, Institute of Medicine. Dietary
Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate,
Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC:
National Academy Press; 1998.
Guyton JR, Bays HE. Safety considerations with niacin therapy. Am J Cardiol.
2007;99:22C-31C. Epub 2006 Nov 28.
Kushi LH, Byers T, Doyle C, Bandera EV, McCullough M,
McTiernan A, Gansler T, Andrews KS, Thun MJ; American Cancer Society
2006 Nutrition and Physical Activity Guidelines Advisory Committee.
American Cancer Society guidelines on Nutrition and Physical Activity
for cancer prevention: reducing the risk of cancer with healthy food
choices and physical activity. CA
Cancer J Clin. 2006;56:254-281.
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.
Larsson SC, Giovannucci E, Wolk A. Vitamin B6 intake, alcohol
consumption, and colorectal cancer: a longitudinal population-based
cohort of women. Gastroenterology.
2005;128:1830-1837.
Wu K, Helzlsouer KJ, Comstock GW, Hoffman SC, Nadeau MR,
Selhub J. A prospective study on folate, B12, and pyridoxal
5’-phosphate (B6) and breast cancer. Cancer Epidemiol Biomarkers Prev.
1999;8:209-217.
Zhang SM, Willett WC, Selhub J, Hunter DJ, Giovannucci EL,
Holmes MD, Colditz GA, Hankinson SE. Plasma folate, vitamin B6, vitamin
B12, homocysteine, and risk of breast cancer. J Natl Cancer Inst.
2003;95:373-380.
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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