February 8, 2023
Vitamins and Minerals

B-Complex Vitamins: A Comprehensive Guide

Major Team

What Are B-Complex Vitamins?

B-complex vitamins are a group of essential nutrients that play various roles in the body. It consists of the vitamins B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folic acid), and B12 (cobalamin).

They are found in various natural foods, including meat, dairy products, leafy greens, beans, peas, and whole or fortified grains. These water-soluble vitamins are crucial for turning food into energy and forming red blood cells.

A Deeper Look Into the B-Vitamins

B1 (Thiamine) 

B1 (thiamine) aids in converting nutrients into energy and is found in higher amounts in pork, fish, sunflower seeds, and wheat germ. A shortage can cause many disorders in the brain and heart that demand a steady energy supply.[1]

B2 (Riboflavin) 

B2 (riboflavin) is an antioxidant and is involved in energy conversion. Long-term riboflavin deficiency has been demonstrated in animal trials to cause brain and heart problems, and some cancers. It is abundant in organ meats, beef, and mushrooms.[2]

B3 (Niacin) 

B3 (niacin) plays crucial roles in cellular processes and is present in foods such as chicken, tuna, and lentils. Deficiencies are rare in industrialized countries due to niacin's presence in most foods and multivitamins. A severe shortage can lead to pellagra, causing symptoms like a sun-exposed skin rash, red tongue, and digestive issues.[3]

B5 (Pantothenic Acid) 

B5 (pantothenic acid) helps with energy absorption from food and hormone/cholesterol production. Foods high in pantothenic acid include liver, fish, yogurt, and avocado. Deficiencies are rare and only occur in individuals with severe malnutrition or genetic mutations that prevent the metabolism of pantothenic acid.[4]

B6 (Pyridoxine) 

B6 (pyridoxine) is essential for amino acid metabolism, red blood cell production, and neurotransmitter synthesis. Pyridoxal 5' phosphate (PLP), its active form, is used to assess B6 levels in the blood. It may lessen cancer risk and benefit pregnancy-related nausea, but it should only be used under medical supervision. Chickpeas, salmon, and potatoes are all high in vitamin B6.[5]

B7 (Biotin) 

B7 (biotin) regulates gene expression and contributes to carbohydrate and fat metabolism. Biotin pills get promoted as an antidote for hair loss and support for healthy hair, skin, and nails. Although a biotin deficiency can cause hair loss and skin or nail problems, evidence of a benefit from supplementing is ambiguous. Yeast, eggs, salmon, cheese, and liver are among its best food sources.[6]

B9 (Folic Acid)

B9 (folate) is paramount for cell growth, amino acid metabolism, red and white blood cell formation, and proper cell division; it also enables DNA and RNA formation and is involved in protein metabolism. A folate deficiency is uncommon as it is abundant in many foods, such as leafy greens, liver, and beans. However, an increased risk can occur in individuals with alcoholism, pregnancy, malabsorption issues, and genetic variants of the MTHFR gene.[7]

B12 (Cobalamin)

B12 (cobalamin) is necessary for neurological function, DNA production, and red blood cell development. B12 supplements and fortified foods contain the free form of B12 for easier absorption. Its food sources are meats, eggs, seafood, and dairy. A severe cobalamin deficiency due to pernicious anemia may require B12 injections.[8]

What B-Vitamins Offer You Collectively

Food into Energy

The majority of B vitamins participate in the process of turning food into energy. Some aid in breaking down fat and protein, while others aid in breaking down carbohydrates. [4] [6]

Although B vitamins are necessary for your body, the effect is different when they are taken as dietary supplements rather than through food. A B-complex supplement may address a specific vitamin gap or shortage, but it cannot offer energy in the form of calories, as does food.

Brain Health

B vitamins are essential for brain health, with B6, B9, and B12 contributing to reducing the risk of cognitive decline and dementia.[9] B12 supports healthy DNA structures and is consequential for fetal development and chronic disease prevention.[10] Vitamin B6 promotes brain development and function, whereas vitamin B9 can lower the risk of brain and spine birth abnormalities such as spina bifida.[7]

Red Blood Cells Production

Red blood cell production depends on several B vitamins, most notably vitamin B12. When there is a vitamin B12 deficiency, the body struggles to create enough red blood cells, frequently resulting in anemia.[11]

Red blood cell development and synthesis also require vitamins B2 and B9. While vitamin B5 aids in creating red blood cells, it also lessens the amount of cholesterol the body produces. Besides, vitamin B6 helps produce hemoglobin, which is necessary for the body's more than 100 different enzymatic reactions and permits red blood cells to transport oxygen through the blood.[12]

Nervous System Health

The neurological system, the skin, and the eyes are all supported by vitamin B2. Moreover, it produces and repairs DNA[2] and supports the proper operation of the neurological and digestive systems. It enables the body's enzymes to function properly and aids in converting food into energy.

Hormone Production

Hormone production in the adrenal glands, such as sex and stress hormones, depends on vitamins B3 and B5.[3] [4] Contrarily, vitamin B6 boosts the neurotransmitters and hormones that control mood and the body's biological clock.[5]

Stress Reduction

B-complex vitamins are not a cure for mental health conditions but may help alleviate symptoms of depression or anxiety. A 60-day study of 60 adults with depression demonstrated that taking a vitamin B complex significantly improved depression and anxiety symptoms compared to a placebo[13]. When combined with antidepressant medication, B vitamins may also enhance treatment response.

Nutrient deficiencies in B vitamins, particularly B12, B6, and folate, have been linked to an increased risk of depression. Therefore, it is advised to test for deficiencies if experiencing depressive symptoms.[14]

Migraine Relief

Research has suggested that vitamin B supplements, including folic acid and vitamins B6 and B12, may help prevent migraines in some people by reducing homocysteine levels. A 2015 report analyzing the effects of vitamin B supplementation on individuals with migraines found a reduction in symptoms associated with migraines with aura, which is characterized by constant headaches with sensory disturbances.[15] 

However, more rigorous research is needed to establish the safety and effectiveness of B vitamin supplementation as a preventive measure for people with chronic migraines.

How Much Vitamin B Is Necessary?

It is fundamental to consider the recommended daily amount based on biological sex, age, and factors like pregnancy, to ensure adequate intake of complex-B vitamins. While a varied diet is typically enough to obtain sufficient B vitamins, some people are at a higher risk of deficiency, such as those over 50, taking antacid medication, or with digestive disorders like celiac or Crohn's disease. 

Similarly, individuals who have undergone stomach or weight loss surgeries, consume alcohol regularly, or follow a vegetarian or vegan diet may also be prone to deficiency. Pregnant or lactating individuals may require more vitamins B6, B12, and folate.[8]

The National Institutes of Health (NIH) establishes the following recommended daily intakes (RDI) for women:

  • B1 (Thiamin): 1.1 mg
  • B2 (Riboflavin): 1.1 mg
  • B3 (Niacin): 14 mg 
  • B5 (Pantothenic acid): 5 mg
  • B6 (Pyridoxine): 1.3 mg
  • B7 (Biotin): 30 mcg
  • B9 (Folic Acid): 400 mcg 
  • B12 (Cobalamin): 2.4 mcg

For men, the RDI is:

  • B1 (Thiamin): 1.2 mg
  • B2 (Riboflavin): 1.3 mg
  • B3 (Niacin): 16 mg
  • B5 (Pantothenic acid): 5 mg
  • B6 (Pyridoxine): 1.3 mg
  • B7 (Biotin): 30 mcg
  • B9 (Folic Acid): 400 mcg 
  • B12 (Cobalamin): 2.4 mcg

Are There Any Side Effects?

B vitamins are generally safe, as they are water-soluble, making it unlikely that someone will consume excessive doses through food or supplements. However, taking supplements with high, unnecessary amounts of vitamin B can lead to serious side effects. 

For instance, excessive doses of B3 may provoke vomiting, high blood sugar levels, skin flushing, and liver damage[16]; elevated doses of B6 can cause nerve damage, light sensitivity, and painful skin lesions.[17] B-complex supplements can also turn urine bright yellow. 

And while folic acid supplements are safe, taking them in large amounts can mask a vitamin B12 deficiency, resulting in neurological damage if the B12 deficiency is not corrected. That is particularly consequential for older adults, who are at greater risk for vitamin B-12 deficiency.

To avoid such risks, one should choose reputable brands that undergo independent testing by organizations like the US Pharmacopeia (USP) when taking B-complex supplements.


1. Martel JL, Kerndt CC, Doshi H, et al. Vitamin B1 (Thiamine) [Updated 2022 Aug 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482360/

2. Office of Dietary Supplements. (2022, May 11). Riboflavin - Health Professional Fact Sheet. National Institutes of Health. Retrieved February 16, 2023, from https://ods.od.nih.gov/factsheets/Riboflavin-HealthProfessional/

3. Meyer-Ficca, M., & Kirkland, J. B. (2016). Niacin. Advances in nutrition (Bethesda, Md.), 7(3), 556–558. https://doi.org/10.3945/an.115.011239

4. Office of Dietary Supplements. (2021, March 26). Pantothenic Acid - Health Professional Fact Sheet. National Institutes of Health. Retrieved February 16, 2023, from https://ods.od.nih.gov/factsheets/PantothenicAcid-HealthProfessional/

5. Office of Dietary Supplements. (2022, June 2). Vitamin B6 - Health Professional Fact Sheet. National Institutes of Health. Retrieved February 16, 2023, from https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/

6. Office of Dietary Supplements. (2022, January 10). Biotin - Health Professional Fact Sheet. National Institutes of Health. Retrieved February 16, 2023, from https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/

7. Office of Dietary Supplements. (2022, November 30). Folate - Health Professional Fact Sheet. National Institutes of Health. Retrieved February 16, 2023, from https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/

8. Office of Dietary Supplements. (2022, December 22). Vitamin B12 - Health Professional Fact Sheet. National Institutes of Health. Retrieved February 16, 2023, from https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/

9. Kennedy, D. (2016). B Vitamins and the Brain: Mechanisms, Dose and Efficacy – A Review. Nutrients, 8(2), 68. MDPI AG. Retrieved from http://dx.doi.org/10.3390/nu8020068

10. Karapiperi K, Gousis C and Papaioannidou P (2010). The role of vitamin B12 in DNA modulation mechanisms. Front. Pharmacol. Conference Abstract: 8th Southeast European Congress on Xenobiotic Metabolism and Toxicity - XEMET 2010. doi: 10.3389/conf.fphar.2010.60.00140

11. Langan, R. C., & Goodbred, A. J. (2017). Vitamin B12 Deficiency: Recognition and Management. American family physician, 96(6), 384–389.

12. Parra, M., Stahl, S., & Hellmann, H. (2018). Vitamin B6 and Its Role in Cell Metabolism and Physiology. Cells, 7(7), 84. MDPI AG. Retrieved from http://dx.doi.org/10.3390/cells7070084

13. Lewis, J. E., Tiozzo, E., Melillo, A. B., Leonard, S., Chen, L., Mendez, A., Woolger, J. M., & Konefal, J. (2013). The effect of methylated vitamin B complex on depressive and anxiety symptoms and quality of life in adults with depression. ISRN psychiatry, 2013, 621453. https://doi.org/10.1155/2013/621453

14. Kate, N., Grover, S., & Agarwal, M. (2010). Does B12 deficiency lead to lack of treatment response to conventional antidepressants?. Psychiatry (Edgmont (Pa. : Township)), 7(11), 42–44.

15. Munvar Miya Shaik, Siew Hua Gan, "Vitamin Supplementation as Possible Prophylactic Treatment against Migraine with Aura and Menstrual Migraine", BioMed Research International, vol. 2015, Article ID 469529, 10 pages, 2015. https://doi.org/10.1155/2015/469529

16. Ellsworth, M. A., Anderson, K. R., Hall, D. J., Freese, D. K., & Lloyd, R. M. (2014). Acute liver failure secondary to niacin toxicity. Case reports in pediatrics, 2014, 692530. https://doi.org/10.1155/2014/692530

17. Vrolijk, M. F., Opperhuizen, A., Jansen, E. H. J. M., Hageman, G. J., Bast, A., & Haenen, G. R. M. M. (2017). The vitamin B6 paradox: Supplementation with high concentrations of pyridoxine leads to decreased vitamin B6 function. Toxicology in vitro : an international journal published in association with BIBRA, 44, 206–212. https://doi.org/10.1016/j.tiv.2017.07.009