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B vitamins are a group of eight essential nutrients that play roles in many organs and bodily systems. Although they can work together in the body, they also carry out their own unique functions.

In this article, we explore the function of B vitamins in the body and some key dietary sources of each.

We also look at the symptoms of each B vitamin deficiency.

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Some people may benefit from taking B vitamin supplements.

B vitamins are important for making sure the body's cells are functioning properly. They help the body convert food into energy (metabolism), create new blood cells, and maintain healthy skin cells, brain cells, and other body tissues.

There are eight types of B vitamin, each with their own function:

Together, they are called the vitamin B complex.

B vitamins often occur together in the same foods. Many people can get enough B vitamins by eating a variety of nutrient-dense foods.

However, those who struggle to meet their daily needs can use supplements.

People may develop B vitamin deficiencies if they do not get enough of the vitamins from their diet or supplements. They may also have a deficiency if their body cannot absorb nutrients properly, or if their body eliminates too much of them due to certain health conditions or medications.

Healthcare professionals recommend that people get a certain amount of each vitamin per day to maintain good health.

The following table provides the daily values (DVs) of each B vitamin according to the Food and Drug Administration (FDA) in milligrams (mg) or micrograms (mcg):

VitaminsDVs for adults and children ages 4+DVs if pregnant or breastfeeding
thiamin (B-1)1.2 mg1.4 mg
riboflavin (B-2)1.3 mg1.6 mg
niacin (B-3)16 mg or equivalent18 mg or equivalent
pantothenic acid (B-5)5 mg7 mg
vitamin B-61.7 mg2 mg
biotin (B-7)30 mcg35 mcg
folate (B-9)400 mcg or equivalent600 mcg or equivalent
vitamin B-122.4 mcg2.8 mcg

Below, we look at each B vitamin in more detail.

The heart, liver, kidney, and brain all contain high amounts of thiamin. The body needs thiamin for:

  • breaking down sugar (carbohydrate) molecules from food
  • creating certain neurotransmitters (brain chemicals)
  • producing fatty acids
  • synthesizing certain hormones

Foods with thiamin

Thiamin is present in:

  • whole grains and fortified bread, cereal, pasta, and rice
  • pork
  • trout
  • mussels
  • acorn squash
  • legumes, such as black beans and soybeans
  • seeds
  • nuts

Thiamin deficiency is not common in the United States. However, certain groups of people may not get enough thiamin, including:

  • those with alcohol dependence
  • older adults
  • those with HIV or AIDS
  • those with diabetes
  • those who have heart failure
  • those who have had bariatric surgery

Symptoms of thiamin deficiency

A person with a thiamin deficiency may experience:

  • weight loss
  • little or no appetite
  • memory problems or confusion
  • heart problems
  • tingling and numbness in the hands and feet
  • loss of muscle mass
  • poor reflexes

Alcohol dependence can cause a person to develop a thiamin deficiency. This can cause Wernicke-Korsakoff syndrome (WKS), which may result in tingling and numbness in the hands and feet, memory loss, and confusion.

WKS can lead Wernicke's encephalopathy (WE), which can be life threatening. A review from 2017 found that people with WE may benefit from high doses of thiamin.

Riboflavin is essential for:

  • energy production
  • helping the body break down fats, drugs, and steroid hormones
  • converting tryptophan into niacin (vitamin B-3)
  • converting vitamin B-6 into a coenzyme that the body needs

Foods with riboflavin

Foods rich in riboflavin include:

  • organ meats
  • fortified breakfast cereals
  • oatmeal
  • yogurt and milk
  • mushrooms
  • almonds

Symptoms of riboflavin deficiency

Riboflavin deficiency is rare but may occur when a person has an endocrine disorder, such as thyroid problems, or certain other conditions.

A person who is deficient in riboflavin may experience:

  • skin disorders
  • sores at the corners of the mouth
  • swelling of the mouth and throat
  • swollen, cracked lips
  • hair loss
  • red, itchy eyes

Having a severe riboflavin deficiency can lead to anemia and cataracts. Being riboflavin deficient during pregnancy can create a higher risk certain birth defects.

People at highest risk of riboflavin deficiency include:

  • those following a vegan diet or who do not consume dairy products
  • athletes who do not eat meat, especially those who also do not eat dairy or other animal products
  • women who are pregnant or lactating, especially those who do not consume meat or dairy products

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Some cereals contain added niacin.

The body converts niacin into a coenzyme called nicotinamide adenine dinucleotide (NAD). NAD is a necessary part of more than 400 different enzyme reactions in the body, the highest of all vitamin-derived coenzymes. These enzymes help with:

  • changing the energy in carbohydrates, fats, and proteins into a form the body can use
  • metabolic processes in the body's cells
  • communication among cells
  • expression of DNA in cells

Foods with niacin

Animal-based foods such as meat, poultry, and fish are high in NAD, which the body can easily use.

Plant-based foods including nuts, legumes, and grains contain a natural form of niacin that the body cannot use as easily. However, manufacturers add niacin to foods such as cereals, and the body can easily use this form.

Symptoms of niacin deficiency

Getting too little niacin can cause a niacin deficiency. Severe niacin deficiency leads to pellagra, which may cause:

If pellagra goes untreated, it can lead to severe memory problems, behavioral changes, and suicidal behavior. It may also lead to an extreme loss of appetite or death.

People at risk of niacin deficiency include those who have:

  • malnutrition
  • anorexia nervosa
  • alcohol use disorder
  • AIDS
  • inflammatory bowel disease (IBD)
  • Hartnup disease
  • carcinoid syndrome, which causes tumors to develop in the gastrointestinal tract

Pantothenic acid is necessary for the body to create new coenzymes, proteins, and fats.

Red blood cells carry pantothenic acid throughout the body so it can use the nutrient in a variety of processes for energy and metabolism.

Foods with pantothenic acid

Many foods contain at least some pantothenic acid, but some of the highest amounts are present in:

  • beef liver
  • shiitake mushrooms
  • sunflower seeds
  • chicken
  • tuna
  • avocados
  • fortified breakfast cereals

Symptoms of pantothenic acid deficiency

Pantothenic acid deficiency is rare in the U.S. because it is plentiful in many foods. However, it may affect people with severe malnutrition. In such cases, they are usually deficient in other nutrients as well.

Symptoms of deficiency include:

  • numbness and burning of the hands and feet
  • headache
  • irritability
  • restlessness and poor sleep
  • a lack of appetite

People with a specific gene mutation called pantothenate kinase-associated neurodegeneration 2 mutation are at a high risk of deficiency.

Vitamin B-6, or pyridoxine, plays a role in more than 100 enzyme reactions. The body needs vitamin B-6 for:

  • amino acid metabolism
  • breaking down carbohydrates and fats
  • brain development
  • immune function

Foods with vitamin B-6

The richest sources of vitamin B-6 include:

  • organ meats
  • chickpeas
  • tuna
  • salmon
  • poultry
  • potatoes
  • fortified cereals

Symptoms of vitamin B-6 deficiency

Many deficiencies in vitamin B-6 are linked to low levels of vitamin B-12, according to the National Institutes of Health (NIH) Office of Dietary Supplements.

Vitamin B-6 deficiency may cause:

  • anemia
  • scaling on the lips
  • cracks at corners of the mouth
  • swollen tongue
  • weakened immune system
  • confusion
  • depression

People at risk of a vitamin B-6 deficiency include those who have:

Manufacturers add biotin to many hair, skin, and nail supplements. However, the NIH state that there is not sufficient evidence to conclude whether taking extra biotin helps with hair, skin, or nails.

Some people believe that biotin may help with psoriasis.

The human body needs biotin for:

  • breaking down fats, carbohydrates, and protein
  • communication among cells in the body
  • regulation of DNA

Foods with biotin

Many foods contain biotin, including:

  • organ meats
  • eggs
  • salmon
  • pork
  • beef
  • sunflower seeds

Symptoms of biotin deficiency

Signs of a biotin deficiency include:

  • thinning of the hair
  • a scaly rash around eyes, nose, and mouth
  • brittle nails
  • depression
  • fatigue

Deficiency is rare in the U.S., but the following groups may be more at risk:

  • people with a metabolic disorder called biotinidase deficiency
  • people with alcohol use disorder
  • women who are pregnant or lactating

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Avocados and some fortified breads are healthful sources of folate.

The natural form of vitamin B-9 is called folate. Folic acid, which is present in fortified foods and some supplements, is a synthetic form of the vitamin.

Because most people cannot take in enough leafy green vegetables for the levels needed in pregnancy, the Centers for Disease Control and Prevention (CDC) suggest that all women of reproductive age who wish to conceive take 400 mcg of folic acid each day, alongside eating a varied diet that contains folate.

When a woman has high enough levels of folate both before and during pregnancy, the fetus has a lower risk of certain birth defects affecting the brain and spinal cord.

Folate is also essential for:

  • DNA replication
  • metabolism of vitamins
  • metabolism of amino acids
  • proper cell division

Foods with folate

The FDA require manufacturers to add folic acid to standardized enriched grain products to help reduce the risk of neural tube defects. People can get folic acid from fortified breads and cereals.

Natural folate occurs in:

  • dark green leafy vegetables
  • beef liver
  • avocado
  • papaya
  • orange juice
  • eggs
  • beans
  • nuts

Symptoms of folate deficiency

The addition of folic acid to grain products has made folate deficiency uncommon. However, the possible symptoms of a folate deficiency may include:

  • weakness
  • headache
  • heart palpitations
  • irritability
  • sores on the tongue or in the mouth
  • skin, hair, or nail changes

The FDA recommend that women increase the intake of folates and take folic acid supplements every day before becoming pregnant and during pregnancy. Other groups who may need extra folate include people who have:

  • alcohol use disorder
  • celiac disease
  • conditions that interfere with nutrient absorption
  • IBD

People should not take more than 1,000 mcg of folic acid each day. Taking more than this can mask symptoms of a vitamin B-12 deficiency. This can cause permanent nerve damage.

Vitamin B-12 contains the mineral cobalt and is sometimes called a "cobalamin." The body uses vitamin B-12 for:

  • creating new red blood cells
  • DNA synthesis
  • brain and neurological function
  • fat and protein metabolism

Foods with vitamin B-12

Vitamin B-12 occurs naturally in animal products such as:

  • clams
  • beef liver
  • salmon
  • beef
  • milk and yogurt

People who do not eat animal products may need to get vitamin B-12 from supplements or fortified foods such as breakfast cereals and nutritional yeast.

Learn more about vegetarian and vegan sources of vitamin B-12 here.

Symptoms of vitamin B-12 deficiency

Vitamin B-12 deficiency usually causes a condition called megaloblastic anemia. Symptoms of a vitamin B-12 deficiency can include:

  • fatigue
  • weight loss
  • constipation
  • loss of appetite
  • numbness and tingling in the hands and feet
  • memory problems
  • depression

People who are at risk of a B-12 deficiency include those who have:

  • conditions that interfere with absorption of nutrients
  • older adults
  • celiac disease
  • Crohn's disease
  • had gastric bypass surgery or surgery on the stomach

Vegetarians, vegans, and people who are pregnant or lactating may also need extra vitamin B-12.

Most multivitamin supplements contain some of each B vitamin, and many provide 100% or more of a person's daily needs for each vitamin.

People can buy B vitamins as individual supplements if they are deficient in only one type. However, some evidence suggests that a full B-complex vitamin supplement may be a better choice, even if a person has just one deficiency.

The researchers state that most people have deficiencies and would benefit from a high-dose B-complex supplement.

Multivitamins and individual vitamin supplements are available to buy in drug stores and online. Choose from a range of B vitamin supplements using the following links:

B vitamins each have their own unique functions, but they depend upon one another for proper absorption and the best health benefits. Eating a healthful, varied diet will generally provide all the B vitamins a person needs.

People can treat and prevent B vitamin deficiencies by increasing their dietary intake of high-vitamin foods or taking vitamin supplements.

Ask a doctor before taking any supplements to be sure they will not interact with medications.