B Vitamins: What Are The Consequences Of Deficiency?

B vitamins are a family of critical nutrients that we typically obtain from the foods that we eat. They support numerous processes in the body at a cellular level. Also, they play an important role in our metabolism (how our bodies turn food into energy) (1).

There are certain similarities between the B vitamins that help explain why they’re grouped together. Firstly, they are all water-soluble (i.e. they dissolve in water), unlike vitamin A, for instance, which is fat-soluble.

Furthermore, B vitamins share some characteristics in the way that they work inside the body. But, although each is different, they can sometimes play a collaborative role too.

For example, folate (vitamin B9) is important in the metabolism of amino acids and vitamins. Meanwhile, cobalamin (vitamin B12) is vital for protein and fat metabolism (2).

However, together they work to metabolize homocysteine (an amino acid) and to support healthy cell division. Whatsmore, folate, relies on vitamin B12 to be utilized inside the body.

B vitamins are not always found in the same foods. However, some foods are excellent sources of many different B vitamins. Particularly rich sources of these compounds include meat, fish, dairy products, and leafy greens (3).

In this article, we’ll look at the unique functions of the B vitamins. We’ll also explore food sources, deficiencies, and answer questions on topics such as B vitamin complex supplements.

The Role of B Vitamins & Food Sources

White and brown eggs

A deficiency in one or more B vitamins can be caused by inadequate dietary intake or an underlying health condition. Some B vitamin deficiencies occur more frequently than others.

For instance, vitamin B12 deficiency affects between 1 in 60 and 1 in 6 US adults depending on the definition used. It is especially common in people who avoid the consumption of animal foods (4).

Symptoms of a nutritional deficiency vary depending on the circumstances. It is advisable to seek testing and treatment from your physician if you suspect you may be deficient in one or more B vitamins.

Nutritional deficiencies can adversely affect the brain and body in a multitude of ways.

Thiamin (vitamin B1)

Thiamin plays an important part in the metabolic system by helping the body utilize carbohydrate intake for energy. It is also involved in the metabolism of fatty acids, steroid hormones, and certain amino acids.

Deficiency in thiamin is uncommon in the United States, in part because foods including wheat flour are fortified with the vitamin. However, the risk may be higher in certain populations, including those with HIV/AIDS and people with alcohol dependence (5).

Foods high in thiamin include whole grains, legumes, nuts, pork, beef, and fortified foods (e.g. bread, rice, pasta)

DV (Daily Value): 1.2mg (adults and children over 4 years) / 1.4mg (if pregnant or breastfeeding) (6)

Riboflavin (vitamin B2)

Riboflavin is involved in the metabolism of drugs, steroids, and fats. Also, it supports energy production and the proper functioning of cells.

Interestingly, riboflavin also works to convert the amino acid tryptophan into niacin (vitamin B3) and helps to convert vitamin B6 into a coenzyme required by the body.

Deficiency in vitamin B2 is extremely rare in the United States. However, it is sometimes caused by certain endocrine disorders (including thyroid hormone insufficiency) (7).

Other populations that may carry an increased risk of deficiency are athletes who follow a vegetarian diet, pregnant or lactating women, and people who follow a vegan diet and/or avoid milk consumption.

Foods high in riboflavin include eggs, milk, yogurt, organ meats (e.g. kidney, liver), fortified grains and cereals, oats, clams, and mushrooms

DV (Daily Value): 1.3mg (adults and children over 4 years) / 1.6mg (if pregnant or breastfeeding)

Niacin (vitamin B3)

Niacin is converted by body tissues into a coenzyme. This coenzyme (NAD) plays a key role in hundreds of other enzyme reactions across the body.

NAD is especially important in reactions that transfer energy from carbohydrates, proteins, and fats into a form that the body can utilize. It is also required for functions including cellular communication and gene expression.

Another coenzyme (NADP) from niacin is involved in the synthesis of fatty acids and cholesterol.

Severe niacin deficiency causes the disease pellagra, which can lead to symptoms including skin discoloration, skin roughness, vomiting, constipation, fatigue, depression, and headache (8).

This degree of niacin deficiency appears very rarely in the United States. However, some groups are more likely to present with low niacin status. These include people with malnutrition, people with Hartnup disease, and people with inadequate intakes of certain vitamins (B2 and B6) and/or iron.

Foods high in niacin include poultry, beef, fish, nuts, legumes, grains, and fortified bread and cereals

DV (Daily Value): 16mg (adults and children over 4 years) / 18mg (if pregnant or breastfeeding)

Panthothenic acid (vitamin B5)

Avodado and egg salad dish

Pantothenic acid is an essential nutrient used by the body to create coenzyme A (CoA). This coenzyme is involved in fatty acid synthesis, among other roles.

Deficiencies are rare because almost all food products contain some pantothenic acid. It can be challenging to identify symptoms of vitamin B5 deficiency because it is usually accompanied by deficiencies in other nutrients (9).

Foods high in pantothenic acid include beef, chicken, whole grains, fortified cereals, mushrooms, seeds, and avocado

DV (Daily Value): 5mg (adults and children over 4 years) / 7mg (if pregnant or breastfeeding)

Vitamin B6

Vitamin B6 plays a part in many processes, including:

  • Protein, carbohydrate, and lipid metabolism
  • Immune function
  • Biosynthesis of neurotransmitters

Deficiency in vitamin B6 alone is uncommon. When it occurs, it is usually linked to low levels of other B vitamins such as vitamin B12 and folate. People with impaired renal function and alcohol dependence are at higher risk (10).

Autoimmune disorders including rheumatoid arthritis, celiac disease, and inflammatory bowel disease are also linked with a low concentration of vitamin B6 and its coenzymes.

Foods high in vitamin B6 include fish, organ meats, poultry, salmon, chickpeas, starchy vegetables, fortified cereals, and bananas

DV (Daily Value): 1.7mg (adults and children over 4 years) / 2mg (if pregnant or breastfeeding)

Biotin (vitamin B7)

Biotin plays a role in the metabolism of glucose, fatty acids, and amino acids. It also has activity in cell signaling and the regulation of genes.

Many people are familiar with biotin supplements because they are regularly touted as beneficial for hair, skin, and nail health. Indeed, biotin deficiency is associated with skin problems, brittle nails, and hair loss.

However, this deficiency is rare in healthy people consuming a typical, mixed diet. Unfortunately, the evidence in support of biotin supplements for hair, skin, and nail health remains weak.

More research is needed before we can draw conclusions on the potential benefits of biotin supplements. However, biotin is safe when taken at recommended doses.

People with alcohol use disorders and pregnant or breastfeeding women may be more likely to have inadequate levels of biotin (11).

Foods high in biotin include eggs, fish, meat, nuts, seeds, and sweet potato

DV (Daily Value): 30mcg (adults and children over 4 years) / 35mcg (if pregnant or breastfeeding)

Folate (vitamin B9)

Certain foods naturally contain folate. Folic acid is a form of folate found in some supplements and fortified foods. The recommended daily intake of folate is higher for pregnant women and women who may become pregnant.

The American College of Obstetricians and Gynecologists (ACOG) advise an intake of 600mcg per day. Pregnant women and women of reproductive age are advised to consider the use of a daily supplement because it can be difficult to achieve the recommended intake from food sources alone (12).

According to ACOG, adequate intake of folate before and during pregnancy helps prevent serious birth defects affecting the brain and spinal cord of the fetus.

The FDA requires manufacturers to enrich breads, pastas, rice, and a multitude of other grain products with folic acid to reduce the risk of birth defects related to inadequate folate intake.

Folate is also critical to cell division and the metabolism of amino acids and vitamins (13).

Groups that may be at a higher risk of folate inadequacy include:

  • People with alcohol use disorder
  • Pregnant women and women of reproductive age
  • People with inflammatory bowel disease

Foods high in folate include green leafy vegetables (such as spinach), fruits (such as avocado), nuts, eggs, meat, and fortified grains

DV (Daily Value): 400mcg (adults and children over 4 years) / 600mcg (if pregnant or breastfeeding)

Vitamin B12

Vitamin B12 is essential for:

  • Forming red blood cells
  • Brain/neurological function
  • DNA synthesis
  • Protein and fat metabolism

Deficiency in vitamin B12 affects between 1 in 60 and 1 in 6 US adults. In some cases, the cause of the deficiency is unclear (4).

However, certain groups are known to have an elevated risk of vitamin B12 deficiency. These include:

  • Vegetarians/vegans
  • Elderly adults
  • People with conditions affecting the absorption of nutrients
  • People who have undergone gastrointestinal surgery
  • People with celiac disease
  • People with inflammatory bowel disease (IBD)

Foods high in vitamin B12 include meat, fish, poultry, eggs, milk, dairy products, and fortified cereals

Vegetarians generally need to consume fortified foods or supplements to reach an adequate intake of vitamin B12. This is because the vitamin is found naturally in animal products.

DV (Daily Value): 2.4mcg (adults and children over 4 years) / 2.8mcg (if pregnant or breastfeeding)

Bottom Line: There are 8 B vitamins in total and each of them supports essential bodily functions. Some B vitamin deficiencies are more common than others. These deficiencies can be caused by underlying health conditions or inadequate dietary intake of the respective nutrients.
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Symptoms of Deficiency

Consult your doctor if you suspect you may have a B vitamin deficiency. They can request a blood or 24-hour urine test to measure the concentration of one or more B vitamins in your body.

B vitamin deficiencies are rare in the United States. However, certain groups of individuals do carry an increased risk of developing a deficiency in one or more B vitamins. It is particularly important to seek out testing if you are displaying symptoms.

Pregnant women and women of reproductive age may benefit from speaking to a doctor about folate (vitamin B9). Adequate intake before and during pregnancy reduces the risk of certain birth defects.

Symptoms of thiamin (vitamin B1) deficiency include:

  • Weight loss and anorexia
  • Muscle weakness
  • Cardiovascular problems
  • Memory loss and confusion
  • Impaired sensory and reflex functions

Thiamin deficiency can lead to beriberi, which is a rare condition characterized by muscle wasting and impaired function.

It may also cause Wernicke-Korsakoff syndrome (WKS). Individuals with alcohol use disorder have an elevated risk of developing WKS. Symptoms include tingling and numbness in the extremities. It may also cause disorientation and memory loss (14).

Symptoms of riboflavin (vitamin B2) deficiency include:

  • Hair loss
  • Sore throat
  • Itchy, red eyes
  • Soreness in the corners of the mouth
  • Skin disorders
  • Cracked lips
  • Reproductive problems

Riboflavin deficiency is very rare in the United States. However, there are some groups that may carry an increased risk. For instance, those with thyroid hormone insufficiency and certain other diseases (7).

Individuals with riboflavin deficiency are often deficient in other nutrients too. Severe cases can lead to impaired metabolism, cataracts, and anemia.

Symptoms of niacin (vitamin B3) deficiency

Severe, prolonged niacin deficiency can cause pellagra (8).

This disease may cause:

  • Pigmented rash
  • A brownish discoloration of skin exposed to the sun
  • Bright, red tongue
  • Constipation
  • Vomiting
  • Diarrhea
  • Neurological changes leading to depression, fatigue, and memory loss

Symptoms of pantothenic acid (vitamin B5) deficiency include:

  • Numbness of the hands and feet
  • Poor sleep
  • Anorexia
  • Headache
  • Fatigue
  • Irritability and restlessness

Pantothenic acid deficiency is rare because the majority of foods contain at least some of this nutrient. However, severe malnutrition can lead to deficiencies in pantothenic acid and other nutrients (9).

Symptoms of vitamin B6 deficiency include:

  • Anemia
  • Swollen tongue
  • Dermatitis (scaling of the lips and cracking at the corners of the mouth)
  • Impaired immune system
  • Depression
  • Confusion

Vitamin B6 deficiency does not usually occur alone. Instead, it is often linked with deficiencies in other B vitamins such as folic acid and vitamin B12 (10).

Mild vitamin B6 deficiencies may not result in noticeable symptoms.

Symptoms of biotin (vitamin B7) deficiency include:

  • Thinning hair
  • Eye inflammation
  • A scaly rash on the face
  • Seizures
  • Brittle nails
  • Depression
  • Fatigue

Biotin deficiency is rare and symptoms of deficiency generally emerge gradually (11).

Symptoms of folate (vitamin B9) deficiency

Folate deficiency is linked to a form of anemia. Symptoms include:

  • Weakness
  • Fatigue
  • Concentration difficulties
  • Headache
  • Palpitations
  • Mouth ulcers
  • Changes in skin, nail, and hair pigmentation

Folate deficiency usually occurs alongside deficiencies in other nutrients. Higher risk groups include people with alcohol use disorder, poor diet, or a condition that affects nutrient absorption in the digestive system (13).

Some researchers have cautioned that excess intake of folate supplements may make it more difficult to diagnosis vitamin B12 deficiency (15).

The tolerable upper intake level of folate for adults is 1000mcg per day. This includes folate from fortified foods and supplements (16).

Folate supplements also have the potential to interact with prescription medicines. Therefore, it is important to speak with your doctor about supplement use before starting or changing a regimen.

Symptoms of vitamin B12 deficiency

Vitamin B12 deficiency is also linked to a form of anemia. Symptoms of which include:

  • Fatigue
  • Appetite loss
  • Weight loss
  • Constipation
  • Poor balance
  • Depression
  • Confusion
  • Mouth soreness

Vegetarians often struggle to obtain sufficient vitamin B12 from their diet alone. This is because the vitamin is generally only found in animal foods (4).

However, fortified foods and supplements can offer an alternative to the consumption of meat, fish, and dairy products.

Bottom Line: B vitamin deficiencies are rare in the United States. You should consult a doctor for a blood test or 24-hour urine test if you are in a high-risk group and experience symptoms of a B vitamin deficiency. A treatment approach can be set up to target the underlying cause of the symptoms if a deficiency is confirmed.
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Addressing Deficiency

Meat, fish, and leafy greens

Testing is the first step in addressing any nutritional deficiency. A doctor or health professional can devise an appropriate course of treatment if a B vitamin deficiency is confirmed.


A 24-hour urine test is designed to gather data from a sample of urine excreted over an entire day. Some B vitamins are eliminated from the body rapidly after ingestion. Therefore, 24-hour tests are used because they may offer greater accuracy than a random urine test (17, 18).

You will be given instructions by your doctor for gathering the urine sample. Generally, you will be asked to empty your bladder first thing in the morning and discard the urine as usual.

After recording the time, you’ll store all urine passed over the next 24 hours in the container(s) provided. Usually, these samples will be stored in cool conditions (for instance, in the refrigerator). You will return the sample to your healthcare provider once you have finished gathering the samples.

Alternatively, your doctor may request a blood test. A health professional will draw a small blood sample using a needle. The blood is collected in a test tube and sent to a lab for analysis (19).

Confirming a deficiency

There are numerous reasons a test can confirm a deficiency in one or more B vitamins. Common causes include:

  • Malnutrition
  • Having a condition that interferes with the absorption of nutrients in the small intestine (e.g. Crohn’s disease, celiac disease)

Talk to your doctor or healthcare provider if you have any queries regarding your results. The treatment approach taken by your doctor will depend on the underlying cause of the deficiency.

The American College of Obstetricians and Gynecologists suggest consuming a daily vitamin supplement containing folic acid if you are pregnant or may become pregnant.

Vitamin B6, folate (vitamin B9), and vitamin B12 all contribute importantly to a healthy pregnancy (20).

Dietary modification

Sometimes a B vitamin deficiency is caused by an underlying health condition. However, deficiencies may also stem from malnutrition or poor diet (21).

In some cases, individuals can benefit from nutrition advice, meal planning, and monitoring from a registered dietitian.

Many whole foods are good sources of a multitude of B vitamins. These include:

The NHS website contains further useful information regarding foods high in B vitamins.

Do B-complex vitamin supplements work?

This question is often asked in expectation of a simple “yes or no” answer. That answer is typically yes but with certain caveats. The usefulness of B-complex supplements will vary from person to person and depend on the nature of their situation.

B-complex vitamin supplements provided a standardized dose of all eight B vitamins. However, supplements containing individual B vitamins are also available. Some research suggests that B-complex vitamin supplements may be a superior choice (22).

People who avoid the consumption of animal foods are advised to consume vitamin B12 supplements or foods fortified with this nutrient.

One of the greatest drawbacks of vitamin supplements is that they cannot replicate the full range of benefits from consuming nutrient-rich whole foods.

Nutritious foods containing B vitamins may also offer a range of other micronutrients, fiber, and antioxidants not available in supplements.

It is important to consult with a doctor or dietitian before beginning the use of a B vitamin supplement. A health professional can offer advice tailored to your circumstances.

Bottom Line: A blood or urine test is the only way to conclusively diagnose a B vitamin deficiency. Once a deficiency is confirmed, your treatment plan will depend on the cause of the deficiency. Supplements may be beneficial in some cases but it is important to consult with a health professional before deciding on a course of action.
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A Final Word

Each of the B vitamins plays essential and unique roles inside the body. A balanced and nutritious diet can generally provide the full intake of B vitamins an individual requires.

People who avoid particular food groups must pay careful attention to their nutritional requirements. For instance, people who avoid animal foods are at risk of developing vitamin B12 deficiency.

B vitamins are critical in order for pregnant women to thrive both before and during conception.

Most B vitamin deficiencies are rare in the United States. Sometimes they can be caused by underlying health conditions.

Remember to consult with a doctor before adding any dietary supplement to your routine.

Alice is staff editor of RightHealth.com and our primary health topics researcher. She is an Applied Medical Sciences graduate of the University of London — a global hub for medical research. Her passion is writing and she strives to make complex subjects accessible to our entire audience. Furthermore, her evidence-based writing model is both scientific and thorough.

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