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Vitamin B Complex

Other common name(s): B vitamins; vitamins B1, B2, B3, B5, B6, B7, B9, and B12

Scientific/medical name(s): thiamin (B1), riboflavin (B2), niacin (B3, also called nicotinamide or nicotinic acid amide), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folic acid or folate (B9), cobalamin (B12)


B vitamins are essential 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 plant and animal food sources.


B vitamins are an important part of the diet and are needed to help avoid many health problems. But, there is not enough scientific evidence to know whether B vitamins can reduce the risk of cancer.

People with low folate intake are at increased risk for certain types of cancer. A diet rich in vegetables and enriched grain products containing this vitamin are recommended by some experts in cancer prevention. (See our separate document, Folic Acid, for more information.) Grain products have been enriched with folic acid for more than a decade, and there is now some concern that folic acid supplements may increase the risk of certain cancers. Supplements are not generally advised except in women of childbearing age and people with restricted food intake.

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 are part of many 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 helps keep the skin, nervous system, and digestive system healthy.
  • 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 or folate) helps the cells in the body make and maintain DNA and is important in producing 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, nervous system function, 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.

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, gives most people with all the B vitamins they need. Only small amounts of these vitamins are needed to reach the recommended dietary intakes. But many people do not eat enough fruits, vegetables, or other healthy foods to get the recommended amounts. And people don’t absorb vitamin B12 as well when they get older. That is why the US Dietary Guidelines recommend that adults over the age of 50 take B12 vitamin supplements, or eat foods enriched with these vitamins, in order to prevent deficiency.

Women who are pregnant or breast-feeding need more folic acid than others. The US Dietary Guidelines recommend that women 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.

Food sources of B vitamins:

  • B1 and B2 are found in cereals, whole grains, and enriched refined 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.
  • B3 is found in liver, fish, chicken, lean red meat, nuts, whole grains, dried beans, and enriched refined grains.
  • B5 is found in almost all foods.
  • B6 is found in fish, liver, pork, chicken, potatoes, wheat germ, bananas, and dried beans.
  • B7 is made by intestinal bacteria and is also in peanuts, liver, egg yolks, bananas, mushrooms, watermelon, and grapefruit.
  • B9 is in green leafy vegetables, liver, citrus fruits, mushrooms, nuts, peas, dried beans, and wheat bread.
  • B12 is found in eggs, meat, poultry, shellfish, milk, and milk products.

Thiamin, riboflavin, and niacin (B1, B2, and B3) have been added to white flour and other refined grains since the 1940s to replace some of the nutrients that are removed with refining. Grain products have had folate added since 1998.

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 and liquid forms. Dosages vary by manufacturer.

What is the history behind it?

While the diseases caused by 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 became clearer, the US 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 on B vitamins and cancer come mainly from animal studies and observational epidemiologic studies. These types of studies are not as strong as randomized controlled clinical trials and must be interpreted with caution.

Some observational studies from the 1990s suggested that folate deficiency was linked with higher risk of colorectal and breast cancer, especially in people who drank alcoholic beverages. But now that folic acid is added to grain products, there are few people with deficiencies. Randomized controlled trials have since suggested that people taking folic acid supplements had higher risk of these cancers than those who didn’t get the folic acid supplements.

Most observational epidemiologic studies have also shown a link between intake of vitamin B6 (as well as blood levels of this vitamin) and lower risks of colorectal cancer. Possible links between other B vitamins and cancer risk have not been studied as extensively or have been studied with mixed results.

Only a few randomized clinical trials of B vitamin supplements have been done. Most of these studies reported that supplements did not reduce cancer risk. In a 2009 study, people given folate and vitamin B6 supplements were more likely to develop and die of cancer than people taking a placebo pill. Results of a large, randomized clinical trial of folate, Vitamin B6, and Vitamin B12 supplements were published in 2012, and there was no effect of these supplements on risk of developing or dying from cancer.

It is still unclear whether taking in more B vitamins will help protect against cancer or increase cancer risk. Some scientists have proposed that inherited differences in the way a person’s body uses B vitamins influence whether these supplements will harm or help a person, and that some day it will be possible to provide a personalized recommendation that might lower cancer risk.

Even if some B vitamins prove to be helpful in preventing certain cancers, it does not mean that B vitamins would be useful in treating cancers. In fact, some experts have cautioned that certain B vitamins, such as thiamin 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 during cancer treatment.

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 healthy 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. Keep in mind that no supplement can take the place of healthy foods. 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 be tested before being 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 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. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.
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.

In general, more problems are caused by not getting enough of the B vitamins than by getting too much. Low thiamin levels can cause weight loss, poor appetite, enlarged heart, and mental problems. Folate deficiency can cause anemia, which worsens over time to cause symptoms like tiredness, weakness, shortness of breath, headache, low energy, poor tolerance of exercise, and trouble concentrating. In pregnant women, folate deficiency can cause serious birth defects of the brain or spinal cord in the infant. Low riboflavin levels can cause sore throat, rashes, and anemia. Low niacin levels can cause pellagra, a syndrome in which a pigmented rash appears on sun-exposed skin. A person with pellagra may have vomiting, constipation or diarrhea, depression, apathy, fatigue, and memory loss. Low pyridoxine levels can cause rash, anemia, and seizures. B12 deficiency can result in anemia. It can also cause brain and nerve problems, such as tingling and numbness in the legs, trouble walking, poor concentration, memory loss, and mood changes. Trouble with vision, sleeping, impotence, and poor bladder and bowel control can also result from B12 deficiency.

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 can vary depending on which B vitamin is taken. Rarely, large doses of vitamin B3 (niacin) supplements can cause blurred vision, nausea, vomiting, high blood sugar, serious liver problems, painful skin lesions, and sensitivity to the sun. High doses of pyridoxine can cause numbness and trouble walking. Folic acid supplements can mask signs of vitamin B12 deficiency and result in more serious damage to the brain and nervous system. Large doses of folic acid may interfere with at least one chemotherapy drug, methotrexate, and other medicines like it. Researchers are now looking into whether extra folic acid can increase the risk of cancer in some people.

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.

To learn more

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).

ACS Guidelines on Nutrition and Physical Activity for Cancer Prevention

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer

Folic Acid


Andreeva VA, Touvier M, Kesse-Guyot E, Julia C, Galan P, Hercberg S. B vitamin and/or ω-3 fatty acid supplementation and cancer: ancillary findings from the supplementation with folate, vitamins B6 and B12, and/or omega-3 fatty acids (SU.FOL.OM3) randomized trial. Arch Intern Med. 2012;172(7):540-547.

Boros LG, Brandes JL, Lee WN, et al. Thiamine supplementation to cancer patients: A double edged sword. Anticancer Res. 1998;18:595-602.

Ebbing M, Bonaa KH, Nygard O, et al. Cancer incidence and mortality after treatment with folic acid and vitamin B12. JAMA. 2009;302(19):2119-26.

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.

Kabat GC, Miller AB, Jain M, et al. Dietary intake of selected B vitamins in relation to risk of major cancers in women. Br J Cancer. 2008;99(5):816-21

Kushi LH, Doyle C, McCullough M, et al; American Cancer Society 2010 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. 2012;62:30-67.

Lawenda BD, Kelly KM, Ladas EJ, et al. Should supplemental antioxidant administration be avoided during chemotherapy and radiation therapy? J Natl Cancer Inst. 2008;100:773-783.

Larsson SC, Orsini N, Wolk A. Vitamin B6 and risk of colorectal cancer: a meta-analysis of prospective studies. JAMA. 2010;303:1077-1083.

Lin J, Lee IM, Cook NR, et al. Plasma folate, vitamin B-6, vitamin B-12, and risk of breast cancer in women. Am J Clin Nutr. 2008;87(3):734-43.

National Institutes of Health, Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin B6. Accessed at http://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/ on January 17, 2013.

US Department of Agriculture Center for Nutrition Policy and Promotion. Dietary Guidelines for Americans, 2010. Accessed at www.health.gov/dietaryguidelines/dga2010/DietaryGuidelines2010.pdf on January 17, 2013.

US Department of Agriculture Center for Nutrition Policy and Promotion. Nutrient Content of the US Food Supply 1909-2000, November 2004. Accessed at www.cnpp.usda.gov/publications/foodsupply/FoodSupply1909-2000.pdf on January 17, 2013.

Wu K, Helzlsouer KJ, Comstock GW, et al. 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.

Zhang SM, Cook NR, Albert CM, et al. Effect of Combined Folic Acid, Vitamin B6, and Vitamin B12 on Cancer Risk in Women: A Randomized Trial. JAMA. 2008;300(17):2012-2021.

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: 01/17/2013
Last Revised: 01/17/2013