Health and Wellness

B-ing Informed: A Guide to B Vitamins

Learn about the eight B vitamins, including their functions, dietary sources, deficiency symptoms, recommended intake, and potential toxicity risks.

Dylan Hembrough, PharmD Candidate

12 Nov 2026 • 7 min read

Photo by Afterave Essentials / Unsplash

“Vitamin B” is sort of a misnomer. The B vitamins are a family of water-soluble molecules with coenzyme activity.¹ Essentially, they assist enzymes in the conversion of food to energy.¹ They are a diverse group of molecules with a variety of functions as well as a variety of adverse effects if you don’t have enough.

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Vitamin B1: Thiamine

Thiamine has a vast range of functions. It is essential for carbohydrate, lipid, and protein metabolism, as well as cellular respiration and fatty acid oxidation.² It plays a role in neurotransmitter synthesis and energy production in mitochondria as well.² Thiamine is found in whole grains, meat, fish, and cereal.³ The recommended daily intake is 1.1-1.2 mg for adults aged 19-50.³

Thiamine deficiency can cause beriberi, a relatively rare disease characterized by peripheral neuropathy and wasting.³ Thiamine deficiency secondary to alcohol use disorder can lead to Wernicke-Korsakoff syndrome, a biphasic disease that, if untreated, can lead to irreversible neural damage and death.³ Wernicke’s encephalopathy is acute and potentially fatal, followed by Korsakoff’s psychosis in survivors.³ Early and rapid intervention during the encephalopathy stage can stave off Korsakoff’s psychosis, but once the psychotic stage is reached, it is largely irreversible.³

Vitamin B2: Riboflavin

Riboflavin is a critical portion of the coenzymes FMN and FAD, which, like thiamine, have a vast array of functions in metabolism and cell growth and development.⁴ Eggs, organ meats, lean meats, milk, and some vegetables contain dietary riboflavin.⁴ The recommended daily intake for adults 19-50 is 1.1-1.3 milligrams.⁴ The body will absorb no more than 27 milligrams of riboflavin in a single dose, and there appears to be no toxicity associated with high doses.⁴

Riboflavin deficiency is also rare but can occur secondary to some endocrine disorders.⁴ Ariboflavinosis is characterized by skin disorders, excess blood, edema of the mouth and throat, reproductive dysfunction, and a general decline of the nervous system and liver.⁴ Long-term deficiency can cause cataracts, which are irreversible with supplements, and anemia.⁴

a grill with eggs and sausages on it — Photo by phoebe lynch / Unsplash

Vitamin B3: Niacin

Niacin is found in large quantities in yeast, milk, meat, and cereal, and plays a role in converting food to energy.^5,6 Its coenzyme form, NAD, is a prerequisite for more than 400 other enzymes in the body.⁶ Adults are recommended to consume 14-16 milligrams of niacin daily.⁵

Niacin also has antilipidemic properties, though it is not first-line.⁵ However, it can be used in patients who cannot tolerate statins or are not reaching their goal cholesterol levels with a statin and dietary modifications.⁵

Niacin deficiency, called pellagra, is also rare in the United States.⁵ Pellagra is serious, however, and can cause irreversible nervous system damage and death if left untreated.⁶ Symptoms of pellagra manifest first in areas with rapid cell turnover or high caloric requirements, leading to diarrhea, photosensitive dermatitis, and dementia.⁶ While most U.S. patients acquire more than enough niacin through their diets, patients with disorders that affect vitamin absorption, alcohol use disorder, or iron-deficiency anemia are at higher risk.⁶ Niacin supplements generally induce recovery within a few days of administration, but secondary pellagra may require additional treatment of the underlying predisposing condition.⁶

Unlike riboflavin, excess niacin can be toxic and lead to skin flushing and dizziness, itching, nausea and vomiting, diarrhea, gout, and liver damage.⁵ Niacin also interacts with some other drugs, raising the risk of liver damage with alcohol, bleeding with anticoagulants, and hypotension with antihypertensives.⁵ It may also affect blood sugar regulation if taken concomitantly with diabetes medication.⁵ Patients taking allopurinol for gout may also need to take a higher dose if they also take a niacin supplement.⁵

Vitamin B5: Pantothenic Acid

Pantothenic acid is important for the production of coenzyme A, a protein involved in the creation and destruction of fatty acids.¹ It is more or less ubiquitous in food, but fortified cereal, sunflower seeds, chicken breast, tuna, and milk contain high levels of pantothenic acid.¹

The recommended daily dose for adults is 5 milligrams.¹ There is no toxic amount of pantothenic acid.¹

Sunflower seeds in a bowl and on a spoon — Photo by Zulfahmi Al Ridhawi / Unsplash

Vitamin B6: Pyridoxine

Pyridoxine is not produced by the body but is essential for more than 100 enzymes involved in the production of DNA, hemoglobin, and neurotransmitters.⁷ Fish, beef, tofu, dairy products, eggs, and fruits and vegetables contain adequate amounts of pyridoxine.⁷ Most adults require 1.2-1.3 milligrams of pyridoxine daily.⁷

It is also critical for breaking down homocysteine.7 Low levels (5-15 μmol/L) of homocysteine are normal, but excess amounts of this amino acid can be indicative of a pyridoxine deficiency and can lead to thrombotic complications.^7,8

Pyridoxine can also be used to alleviate morning sickness, or nausea during pregnancy.⁷

The threshold for pyridoxine toxicity is high (100 milligrams daily), but above this amount, patients may experience neuropathy, photosensitivity, nausea, and ataxia.⁷ Dietary pyridoxine is not present in high enough levels to approach this threshold, but prolonged supplement use can tip the scale.¹

Vitamin B7: Biotin

Like its B vitamin cousins, biotin is important for metabolism of carbohydrates, proteins, and fats.¹ It is found in eggs, salmon, pork, beef, and some vegetables and nuts.¹ It is often included in hair and nail care products, and while biotin can strengthen hair and nails, biotin deficiency has yet to be determined as the direct cause of weak hair or nails.¹ But, biotin can never hurt – there is no upper limit for human consumption.¹ The recommended daily dose for most adults is 30 micrograms daily.¹

A bottle of pills and a rose on a table — Photo by Afterave Essentials / Unsplash

Vitamin B9: Folate

Folate shines brightest in prenatal care – it is absolutely essential for the formation of the neural tube in the fetus.¹ The neural tube is a precursor to the brain and spinal cord, and its formation occurs so early in pregnancy that the patient may be unaware they are pregnant.¹ Folate is thus recommended for patients trying to become pregnant and is often present in prenatal vitamins.¹ Most adults require 400 micrograms of folate daily, but pregnant women should have 600 micrograms daily.¹

In developing fetuses, folate deficiency adversely affects the development of the neural tube and often leads to spina bifida.⁹ This condition arises when the neural tube fails to close, leading to incontinence, numbness, and leg paralysis.¹⁰ Another more serious neural tube defect that can result from folate deficiency is anencephaly, where a baby is born missing parts or all of their brain or skull.¹¹ Anencephaly is fatal and often results in miscarriage or stillbirth.¹¹

In adults, folate is crucial for red blood cell health and the formation of DNA and RNA. Folate deficiency manifests most often as folate deficiency anemia.⁹ The body produces dysfunctional red blood cells in this condition, and complications include infertility, cardiovascular disease, and decreased cognitive function.⁹ Adequate folate is usually acquired from a healthy diet, as it can be found in many fruits and vegetables, eggs, dairy, seafood, and meat, and foods like bread, pasta, rice, and cereal are often fortified with it.⁹

Vitamin B12: Cobalamin

Cobalamin is a cobalt-containing molecule and is also crucial in red blood cell and DNA formation.¹ The body does not make cobalamin, but it is relatively common in meat and dairy products.^1,12 Most adults require 2.4 micrograms daily.¹

Like folate, cobalamin deficiency can lead to vitamin B12 deficiency anemia and red blood cell dysfunction.¹² Symptoms of cobalamin deficiency include fatigue, weakness, nausea and vomiting, diarrhea, weight loss, sore mouth or tongue ulcers, and pale skin.¹² Cobalamin is important for neural function as well, so a deficiency can also cause numbness in the extremities, vision problems, confusion and memory loss, difficulty walking or speaking, depression, and irritability.¹²

Untreated cobalamin deficiency can lead to irreversible peripheral neuropathy, paralysis, memory loss, and incontinence, among other symptoms.¹²

Cobalamin also has a very close relationship with intrinsic factor, a protein produced by the stomach lining that is essential for absorption of the vitamin.¹³ The parietal cells of the stomach, which also produce hydrochloric acid, are responsible for making intrinsic factor, putting patients taking proton pump inhibitors at higher risk of complications.¹³ Pernicious anemia, a form of cobalamin deficiency, can develop from autoimmune gastritis, where the immune system targets parietal cells for destruction.¹³

Those at highest risk include vegans and vegetarians, patients taking metformin or a proton pump inhibitor, patients who have undergone bariatric surgery, patients with alcohol use disorder, and patients over the age of 65.^1,12 A synthetic form of vitamin B12, called cyanocobalamin, can be prescribed to treat pernicious anemia and cobalamin deficiency.¹⁴

Talk to your doctor before taking any vitamin supplements, especially those with a toxic ceiling. If you are pregnant or planning to be, speak with your doctor about vitamin requirements – particularly folate.

References

*Information presented on RxTeach does not represent the opinion of any specific company, organization, or team other than the authors themselves. No patient-provider relationship is created.