B vitamins are essential to human life and are found in every body cell. Among their many roles, B vitamins are involved in turning food into energy, cell replication and cell growth.

Each type performs a specific role in the body and, together, they form complex, interdependent relationships.

The nine commonly recognized B vitamins are:

• B1 (thiamine)
• B2 (riboflavin)
• B3 (niacin, nicotinic acid, nicotinamide or niacinamide)
• B5 (pantothenic acid)
• B6 (pyridoxine, pyridoxal or pyridoxamine)
• B9 (folate or folic acid)
• B12 (cobalamin)
• Biotin (sometimes called vitamin B7)
• Choline

While the B vitamins are necessary for chemical processes within the body, overdoses or deficiencies may harm a person’s health. Excessive supplement use is the only known cause of vitamin B overdoses. Depending on the vitamin, the results range from only mild symptoms to severe nerve damage. Deficiency may be the outcome of an improper diet or inability to absorb the vitamin. Initial symptoms include fatigue and diarrhea, but serious diseases result when left untreated, possibly leading to death.

B vitamins are a group of related vitamins that are essential to body function. Each acts both independently and together with other B vitamins to assist chemical reactions in the body. Due to their interdependence, B vitamins are often discussed as a group. In fact, when first discovered, they were thought to be one vitamin.

Vitamins are organic compounds obtained from dietary sources and necessary for good health. Their existence was first recognized in the early 20th century and their letter names correspond to the order in which they were discovered. When individual B vitamins were discovered, they were assigned numbers. Later names were given for each that relate to their chemical formulas.

B vitamins come from many sources and a balanced diet will typically fulfill the body’s needs. They are also available as supplements, both as individual vitamins and as the entire B-complex group.

Vitamins are water-soluble or fat-soluble molecules, which determines how they travel through the body and how they are stored. Being water-soluble, most B vitamins move freely through the body and cells. They are not stored in tissues and must be consumed or manufactured by the body regularly.

Inside cells, B vitamins act as coenzymes, compounds that make many chemical reactions within the body possible. Some of the reactions utilizing B vitamins are necessary for growth and the metabolism of carbohydrates, fats and proteins. In addition to their involvement in chemical reactions, some B vitamins are structural components of cells, such as B1 in the myelin sheath of nerve cells.

B vitamins are essential, meaning that the body either does not produce them itself or does not produce enough to meet its needs. The body is able to produce small amounts of B3, B5, folate (B9), biotin and choline. Most B vitamins are used and quickly eliminated from the body. The exception is vitamin B12, which the body is able to recycle and reuse.

The body’s ability to absorb several of the B vitamins through the gastrointestinal tract diminishes with age. Therefore, physicians often recommend supplements or fortified foods for patients over age 50. Vitamins in these products are in forms that are often easier to absorb than those that occur naturally. Supplements may also be recommended for vegetarians or vegans to replace those B vitamins that are naturally available only in animal products.

Because B vitamins work in complex interrelationships, a deficiency of one may impact the function of others. While this may initially cause only mild symptoms, it can frequently progress to serious or even life-threatening conditions. In industrialized nations, vitamin B deficiencies are rare because adequate intakes are easily achieved with a balanced diet.

The B vitamins are involved in chemical processes that take place throughout the body. All are involved directly or indirectly in energy metabolism and growth. The nine B vitamins and their functions are:

• B1 (thiamine). Found on the myelin sheath of nerve cells and aids communication between nerves and muscles, including the heart. Each cell depends on B1 to help convert carbohydrates to energy. B1 also plays a role in the production of hydrochloric acid, making chemical digestion of food possible.
  
  
• B2 (riboflavin). Like vitamin B1, B2 helps release energy from carbohydrates. It is also involved in breaking down fats and proteins. B2 is necessary for cell development and function, and may also play a role in producing red blood cells.
  
  
• B3 (niacin, niacinamide, nicotinic acid or nicotinamide). Helps metabolize glucose, fat and alcohol. B3 is also needed by the body to make new cells and create fatty acids and steroids. The forms found naturally in food are nicotinic acid and nicotinamide. Niacin and niacinamide are used in dietary supplements, which may be prescribed in large doses to reduce low density lipoproteins (the “bad cholesterol”) and increase high density lipoproteins (the “good cholesterol”). B3 is one of the few B vitamins that the body can produce (from the amino acid tryptophan), although in smaller amounts than it needs.
  
  
• B5 (pantothenic acid). Involved in more than 100 metabolic pathways for the conversion of carbohydrates, proteins and fats. B5 is also necessary to make lipids, neurotransmitters and hemoglobin. The body produces some B5 itself, but not enough to meet its needs.
  
  
• B6 (pyridoxine, pyridoxal or pyridoxamine). Involved in many body processes, including making amino acids, converting tryptophan to B3 and maintaining blood glucose levels. In the nervous system, it is necessary for the synthesis of the neurotransmitters serotonin, dopamine, and norepinephrine, which influence mood and appetite. Within the circulatory system, B6 is required to make hemoglobin.
  
  
• B9 (folate or folic acid). Necessary to create and maintain cells because of its involvement in the synthesis of proteins and DNA (which controls cell function and transfers genetic information to the next generation of cells). B9 is essential in the earliest stages of pregnancy for fetal health due to its role in preventing neural tube defects in infants. Folic acid is the synthetic form of the vitamin and is more easily absorbed than the natural form. Folate can be produced by the body, but not in amounts large enough to meet the body’s needs.
  
  
• B12 (cobalamin). The only B vitamin that requires a specific chemical (intrinsic factor [IF]) to be absorbed into bloodstream. B12 is essential for the nervous system, creation of red blood cells and making DNA. It is also part of a coenzyme involved in the metabolism of amino acids and fatty acids.
  
  
• Biotin (sometimes called vitamin B7). Involved in metabolism of some fatty acids and amino acids. It is also involved in the synthesis of glucose. Biotin is made by bacteria in the gastrointestinal tract, but not enough is produced to meet the body’s needs.
  
  
• Choline. Involved in fat metabolism and transport. It is also necessary for the synthesis of several neurotransmitters. The human body is able to make this compound, but it is not known whether the body makes enough to meet its needs. While it may actually be a nonessential vitamin, it is most typically classed with other B-complex vitamins as essential.

The National Academy of Sciences (NAS) established dietary reference intakes (DRIs) to maintain a healthy body. The recommendations are categorized by gender and age. The suggestions for women also incorporate pregnancy and breastfeeding. For some age groups and vitamins there is scientific uncertainty as to what intake is necessary for daily function. For these groups, the NAS provides adequate intakes (AIs). AIs provide the mean intake of breastfed infants (children younger than 12 months) and the minimum to prevent deficiency of the vitamins B5, biotin and choline.

For the B vitamins, the recommendations are measured in either milligrams per day (mg/d) or micrograms per day (¼g/day).

Vitamin B DRI Recommendations: Males

Vitamin B DRI Recommendations: Females

Vitamin B DRI Recommendations: Children

The B vitamins are available from a variety of dietary sources. Therefore, a balanced diet usually provides sufficient vitamin B to satisfy the needs of the human body.

Natural Sources of B Vitamins

In addition to naturally occurring nutrients, some foods have them added during processing. Such products are called enriched foods or fortified foods, and the process frequently includes many of the B vitamins. These foods include many bread, rice, cereal and yeast products. Such foods are often critical in a vegetarian or vegan diet to provide non-animal sources of B vitamins that are naturally found only in animal products.

While many foods are good sources of B vitamins, the way those foods are prepared can affect their nutrient content. B vitamins can be destroyed during food preparation and processing, including:

• Boiling. B vitamins are water-soluble. Therefore many leach out of foods and into cooking water when boiled.
  
  
• Overcooking. Vitamins B1, B5, B6 and folate are vulnerable to heat and may be destroyed if cooked at too high a temperature or for too long.
  
  
• Exposure to oxygen. Folate is vulnerable to air exposure and it may be lost when cut vegetables are allowed to sit long periods.
  
  
• Exposure to light. Light destroys vitamin B2, part of the reason milk is often sold in semi-translucent plastic bottles or cardboard boxes.
  
  
• Freezing, canning and refining. These processes can destroy vitamin B5.
  
  
• Microwave cooking. Aside from issues of heat and water leaching, B12 is unique among the B vitamins because it can be destroyed by microwave cooking.

In most industrialized nations, the average diet contains sufficient B vitamins to meet the body’s needs. Under certain conditions, a physician may recommend vitamin supplements if the patient’s system is unable to use or absorb the nutrients from food sources. The B vitamins are often grouped together in one dose in B complex supplements, which may also contain other compounds that may be of benefit. Most widely available multivitamins also include sufficient quantities of the B complex.

Oral supplements are also available for some individual B vitamins, including B3, B6, folic acid and B12. Other forms of B12 are also available for patients unable to absorb the nutrient through the stomach (e.g., injection, nasal gel).

Differences in the body’s ability to absorb or synthesize some B vitamins from foods and supplements make measuring their vitamin content complex. Nutritional scientists have developed ways to compare the quantities available. These include:

• Niacin equivalents (NE). Nutritional information for foods expresses the amount of B3 available as niacin equivalents. This is the total B3 available directly plus the amount the body can make from the amino acid tryptophan. Each NE equals one milligram (mg) of niacin or 60 mg of tryptophan.
  
  
• Dietary folate equivalents (DFEs). Dietary supplement labels include the amount of folate as dietary folate equivalents. This is because the body is able to use synthetic folic acid more efficiently than folate from food. The DFE is determined by multiplying the micrograms (µg) of synthetic folic acid present, then adding the (µg) of food folate.

B vitamins are essential for the body to function. Without them, cells would be unable to divide, grow, communicate or metabolize food into energy (see Types and differences). Supplementing certain or all B vitamins may also be a part of established treatments for a variety of conditions, including:

• Pregnancy. Pregnant women require additional nutrients for themselves and their developing babies. B vitamins are particularly important to reduce the risk of neural tube defects. The fetal neural tube develops into the brain and spinal cord and is sensitive to vitamin deficiency in the earliest stages of pregnancy. Folate is highly recommended to women who could become pregnant as a preventative method for spina bifida and other neural tube-related birth defects. B vitamins are included in most prenatal supplements.
  
  
• High cholesterol. The plaque build up associated with high cholesterol can be deadly. Among the treatments available, is B3 (niacin) supplementation. In prescribed doses, the vitamin causes a significant increase in the high-density lipoproteins (HDL, the “good cholesterol”) and a lesser decrease in low-density lipoproteins (LDL, the “bad cholesterol”). For some patients, B3 is prescribed in conjunction with other cholesterol medications.
  
  
• Atherosclerosis. In addition to its known benefits in treating cholesterol, vitamin B3 is being studied as part of a treatment aimed at slowing the hardening and narrowing of the arteries.
  
  
• Vitamin deficiency. The body may not get enough B vitamins to meet its needs due to a poor diet or a condition that keeps the body from properly absorbing or using nutrients. Supplementation of B vitamins may be temporary or life-long depending on the cause of the deficiency (see Overdose and deficiency).
  
  
• Metabolic disorders (e.g., Leigh disease, maple syrup urine disease, lactic acidosis). With such conditions, the body is unable to make the thiamin pyrophosphate needed for energy metabolism. The body needs vitamin B1 to make thiamin pyrophosphate and, therefore, B1 supplements may increase its production.
  
  
• Neonatal jaundice (yellowing of the infant’s skin, eyes and body fluids). It results from a variety of causes and the treatment often depends on diagnosis of the cause. When phototherapy is used for treatment, it is often in conjunction with vitamin B2 supplements.
  
  
• Hereditary sideroblastic anemia. Patients with this disease are unable to make normal red blood cells. Treatment often involves B6 supplements which assist in the production of red blood cells.

Research continues to investigate the link between B vitamins and a number of other conditions. The effectiveness of B vitamin supplementation is being studied in the treatment and prevention of these conditions, including:

• Dementia and cardiovascular disease. Homocysteine is an amino acid found in high levels in patients suffering from heart disease, blood clots, strokes and Alzheimer disease. Reducing homocysteine levels is possible with B6, folate and B12, but it has not been shown to improve cognitive ability or reduce the risk of heart disease.
  
  
• Cancer. Several studies are focused on a possible link between taking folate supplements and a lower risk of developing some types of cancer. This may relate to folate’s role in the synthesis and maintenance of DNA, the genetic material that directs cell functions. A direct link between the vitamin and disease has yet to be understood, and use of folate supplements without the guidance of a physician may be dangerous.

The complex relationships between some B vitamins and the human body can be disrupted by medications or medical procedures. Such factors may:

• Prevent the body from absorbing the vitamins
• Destroy the vitamins before they can be used
• Prevent the vitamins from performing their body functions

Drinking alcohol results in all three of the above factors to some extent. Therefore overuse or abuse of alcohol can lead to severe B vitamin deficiency. In industrialized countries where balanced diets are easily attained, alcoholism is the leading cause of B vitamin deficiency.

In many cases, taking in additional B vitamins in supplemental form may be needed in conjunction with certain medical conditions. Treatments or medications requiring greater intake of all the B vitamins include:

• Diuretics. Medications that increase urine output. They are used to treat conditions such as high blood pressure, cancer and edema (swelling).
  
  
• Dialysis A process to remove waste products from the blood in patients whose kidneys are damaged and therefore unable to perform this function.

Medications frequently interact with specific vitamins. Examples of these interactions include:

• Folate. Of the B vitamins, folate may be the most susceptible to interactions with drugs. Antimetabolites (e.g., methotrexate), used in the treatment of some cancers, rheumatoid arthritis, psoriasis and several other diseases, may block cells from using the vitamin. Other factors that may impact the body’s ability to use folate include regular use of aspirin, antacids, oral contraceptives and cigarettes. In addition, high doses of folic acid (synthetic folate) have been found to interact with anticonvulsant drugs (e.g., dilantin, phenytoin, primidone).
  
  
• B12. Medications used to treat gastroesophageal reflux disease (GERD) and peptic ulcers (e.g., proton pump inhibitors, H2 receptor antagonists) reduce the amount of hydrochloric acid produced in the stomach and have the potential to interfere with B12 absorption.  However, there have not yet been any confirmed cases of these medications causing vitamin B12 deficiency, even after long-term use.   Medications to treat diabetes may also reduce B12 absorption by interfering with calcium metabolism.

At the proper levels, the B vitamins are necessary for the human body to function. Too little or too much of them stresses cells and tissues and may lead to serious, life-threatening disease.

Signs and symptoms of consuming too much or too little of the B vitamins include:

Overdoses of B vitamins from food have not been documented. Instead, the limited reports of toxicity are the result of taking excessive supplements. In general, overdoses stress the kidneys, but rarely cause permanent damage. B6 is unique among the B vitamins because overdoses are known to cause nerve damage. However, this damage is reversible when supplementation is stopped. Overdoses of folate may mask symptoms of B12 deficiency, possibly leading to permanent nerve damage.

In contrast to the relatively limited reports on vitamin B toxicity, a long list of conditions is related to their deficiency. They include:

• Beriberi (severe B1 deficiency). Can affect the cardiovascular system (wet beriberi) or the nervous and muscular systems (dry beriberi). Without treatment, beriberi can lead to paralysis, heart failure and death. Wernicke-Korsakoff Syndrome is also a thiamine deficiency (a brain disorder caused by the lack of vitamin B1).  Thiamine deficiencies are common in chronic abusers of alcohol.
  
  
• Ariboflavinosis (severe deficiency of B2). Rarely occurs alone and is treated in conjunction with other vitamin deficiencies.
  
  
• Pellagra (B3 deficiency). More common in places where diets are heavily dependent on corn. Without treatment, it will eventually lead to death.
  
  
• B5 deficiency. Rare because B5 occurs in so many foods. However, it can impact every system of the body.
  
  
• B6 deficiency. Mild deficiency is common, but severe cases are rare. Alcoholics and older adults are more likely to have inadequate vitamin B6 intakes because they have often have limited variety in their diet. Alcohol also promotes the destruction and loss of vitamin B6 from the body.
  
  
• Folate deficiency. Can cause a variety of conditions. General deficiency of folate may cause megaloblastic anemia and is indistinguishable from the body’s reaction to too little B12. During early pregnancy, folate deficiency in the mother can cause low birth weight, neural tube defects such as spina bifida, and separation of the placenta from the uterine wall. In children, folate deficiency can lead to slower than average growth. Folate deficiency has also been observed in alcoholics. Alcohol interferes with the absorption of folate and increases the excretion of folate by the kidney. In addition, many people who abuse alcohol have poor quality diets that do not provide the recommended intake of folate.
  
  
• B12 deficiency. May take 20 years to develop because B12 is repeatedly recycled in the body. Long-term deficiency (pernicious anemia) may lead to paralysis as a result of the degeneration of nerve cells in the spine, brain and extremities. Strict vegetarians and vegans are at a greater risk of developing B12 deficiency than lacto-ovo vegetarians and non-vegetarians because natural food sources of vitamin B12 are limited to foods that come from animals. Also, breast-fed infants of women who follow strict vegetarian diets have limited reserves of vitamin B12 and can develop a vitamin B12 deficiency.
  
  
• Biotin deficiency. Rare due to the wide variety of foods containing biotin. Reported cases have been linked to intravenous (I.V.) feeding without supplementation and excessive ingestion of raw egg whites (possibly consumption of 12 or more raw eggs a day).
  
  
• Choline deficiency. Rare due to the body’s ability to make this vitamin and its presence in many foods.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following B vitamin-related questions:

1. Am I at risk for B vitamin deficiency or toxicity?
   
   
2. Are there any B vitamins I should take more of or avoid for health reasons?
   
   
3. How can I learn more about sources of vitamins and how much I need each day?
   
   
4. Should I consult a registered dietitian to reduce my risk of vitamin B deficiency or overdose? Can you recommend one?
   
   
5. What early signs and symptoms of B vitamin deficiency should I be on the lookout for?
   
   
6. Can you tell if my deficiency is from diet or in my ability to absorb the vitamin? What difference does this make in my treatment?
   
   
7. If I need treatment for my vitamin deficiency, how long will it last?
   
   
8. Is it possible for me to take too many B vitamins?
   
   
9. How will I know if I am consuming too many B vitamins?
   
   
10. Based on my current level of alcohol intake, should I be concerned about alcohol’s affects on B vitamins in my body?