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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, 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. This is especially important in turning food into energy and
other needed substances. B vitamins are found in a variety of plant and
animal food sources.
Overview
While B vitamins are an important part of the diet and are
needed to help avoid many health conditions, there is not enough
scientific evidence to know whether B vitamins can reduce the risk of
cancer. Vitamin B9 (folic acid) may have some protective effect against
certain cancers, but more studies are needed to confirm this (see Folic
Acid). Available scientific evidence does not support claims
that B
vitamins are 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) also 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 of 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. All women of childbearing age are urged to increase
their intake of folic acid 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. However, available scientific
evidence has not found any effect of B vitamin supplements on the
growth and spread of 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
grain products, fruits, and vegetables is sufficient to provide the
body with all the B vitamins it needs. 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 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 of the 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 evidence?
The limited data concerning B vitamins and cancer comes
mainly from animal studies and from studies that observed large numbers
of people. 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 studies looking at large groups
of people (population studies) showing that increased intake of vitamin
B9 (folic acid) is linked to a lower risk of colon cancer, especially
in people where some are vitamin deficient (such as those who drink
excess amounts of alcohol). The evidence has been mixed thus far for
most other types of cancer (see Folic
Acid).
Some (but not all) of the studies looking at large groups of
people 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
been less well-studied 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 an increase in B vitamin intake will help protect
against cancer, or what intake levels 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. Choose whole grains over
refined grains and sugars, and limit high-fat and processed meats.
Select foods that help maintain a healthy weight. It is also important
to engage in moderate to vigorous physical activity for 30 to 60
minutes 5 or more days per week. For most people, this will help keep
weight under control, reduce risk of some cancers, and reap many other
health benefits. While it is best to get vitamins and minerals from
foods, supplements may be helpful for some people, such as pregnant
women, women of childbearing age, and people with restricted food
intakes. 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.
Are there any possible problems
or complications?
This product is sold as a dietary supplement in the
United States. Unlike drugs (which must be tested before being allowed
to be sold), the companies that make supplements are not required to
prove to the Food and Drug Administration that their supplements are
safe or effective, as long as they don't 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). Actual amounts per dose may vary between
brands or even between different batches of the same brand.
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.
Some possible side effects include gouty arthritis, high blood sugar
levels, and skin problems. Overdoses can lead to heart and liver
problems. Large doses of niacin supplements can rarely cause blurred
vision, nausea, vomiting, and can sometimes make stomach ulcers worse.
High doses of folate supplements may interfere with at least one
chemotherapy drug, methotrexate and similar medicines. (See also Folic
Acid.) 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, 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 ordered
from our toll-free number (1-800-ACS-2345).
References
Boros LG, Brandes JL, Lee WN, et al. Thiamine supplementation
to cancer patients: A double edged sword. Anticancer Res.
1998;18:595-602.
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
Mar 19;99(6A):22C-31C.
Kushi LH, Byers T, Doyle C, et al. 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.
Labriola D, Livingston R. Possible interactions between dietary
antioxidants and chemotherapy. Oncology.
1999;13:1003-1008.
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, et al. 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.
Revised: 06/19/2007
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