The water-soluble vitamin B12 is found naturally in some foods and also available as a dietary supplement and prescribed natural ingredient. Vitamin B12 plays a part in numerous essential body functions, and deficiency of this vitamin can have widespread health implications. Fortunately, there are plenty of ways to get enough B12 from food and supplements.

Keep reading to learn more about vitamin B12 benefits, deficiency symptoms and implications, and best sources.

Vitamin B12 benefits

Understanding the value of vitamin B12 requires a quick reminder of the importance of DNA synthesis. DNA provides the template that cells use to function properly. When DNA synthesis is impaired, cells can’t replicate and can become damaged or dangerous. Vitamin B12 is critical to DNA synthesis and is required for optimal cellular energy production throughout the entire body. (8)

Besides its influence on DNA, vitamin B12 is also required for optimal neurological and cardiovascular function, as well as blood cell formation. (6) Specific to cardiovascular disease, the connection between vitamin B12 and the heart is via homocysteine, an amino acid that must be broken down by B vitamins in order to be utilized in the body. High homocysteine levels are linked to an increased risk of heart disease with one meta-analysis finding that every 5 μmol/L of increased homocysteine resulted in a 20% increased risk of heart disease independent of other risk factors. (2) Research also shows that vitamin B12 deficiency is linked to a corresponding increase in homocysteine levels. (4)


Woman typing on a calculator
B12 is required for normal neurological function.


As for neurological function, research demonstrates that vitamin B12 deficiency can contribute to several neurological diseases such as seizures, psychiatric disorders, dementia, and others across the lifespan. These results may be attributed to the neuroprotective effects of vitamin B12. (5)

Much of the research on vitamin B12 benefits focuses on correcting deficiency because vitamin B12 deficiency can have significant negative health ramifications.

Dangers of vitamin B12 deficiency

In the United States, a degree of vitamin B12 deficiency is considered fairly common with approximately 15% of adults aged 20 to 59 being marginally deficient and more than 20% of people over age 60 being deficient. (11) The most important clinical aspect of deficiency is that even mild vitamin B12 deficiency can lead to neurocognitive issues and other negative health consequences. As a result, timely diagnosis and early intervention via diet and/or dietary supplements is essential. (1)

There are many diverse causes of vitamin B12 deficiency including:

  • Bacterial overgrowth
  • Certain pharmaceutical medications, such as metformin and proton-pump inhibitors
  • Gastric bypass surgery
  • H. pylori infection
  • Malnutrition/malabsorption
  • Pernicious anemia
  • Vegetarian or vegan diet (7)

Vitamin B12 deficiency symptoms

The symptoms of vitamin B12 deficiency are diverse and can vary from neurological (e.g., dizziness, fatigue, cognitive issues) to psychiatric (e.g., depression, mood changes). (12)

Vitamin B12 deficiency impacts multiple systems with sequelae that can manifest in a variety of ways including:

  • Anemia, leukopenia, pancytopenia, or thrombocytopenia
  • Fatigue upon exertion, including heart palpitations and skin pallor
  • Hyperpigmentation, jaundice, or vitiligo
  • Mental health issues, such as irritability, forgetfulness, or even acute psychosis (3)

Vitamin B12 deficiency is also linked to symptoms of depression. In one study involving community-dwelling, older disabled women, there was a twofold increase of severe depression in the women who were deficient in vitamin B12. (10)

It’s clear that preventing and reversing vitamin B12 deficiency is an important clinical objective, and that’s accomplished via diet and/or dietary supplements.

Vitamin B12 foods

Given that the body does not manufacture vitamin B12, it must come from the diet or dietary supplements. The following Recommended Dietary Allowances (RDA) have been established for vitamin B12. (6)


B12 requirements by age
Each age group requires different amounts of vitamin B12 each day.


Foods containing the highest amounts of vitamin B12 include eggs, fish, meat, milk and milk products, and poultry. The following table outlines dietary sources of vitamin B12 and respective amounts per serving. (6)




Foods that contain vitamin b12 chart
B12 can be found in various animal-based foods.


Non-animal sources of vitamin B12 include fortified cereals and some nutritional yeast products. (7) While diet is a key way to prevent vitamin B12 deficiency, certain individuals, such as older individuals and those following plant-based diets, may find it challenging to consume enough vitamin B12 through diet alone.

Plant-based diets

As indicated previously, a vegetarian or vegan diet can increase the risk of vitamin B12 deficiency. According to a 2015 review, vitamin B12 deficiency may negate the heart disease prevention benefits of the vegetarian diet, and for that reason, individuals on these diets should speak to their healthcare provider about taking a vitamin B12 supplement daily. (9)

Older individuals

Another high-risk population for vitamin B12 deficiency is older individuals due to malabsorption issues commonly experienced by these individuals. Because dietary vitamin B12 is not as efficiently absorbed as one ages, people over the age of 51 should consider taking a vitamin B12 supplement to get the amount they need to reduce the potential ill effects of long-term vitamin B12 deficiency. (1)

The bottom line

Low vitamin B12 levels can have dangerous health ramifications. As vitamin B12 plays an important role in the body, it’s critical that practitioners proactively work to prevent and reverse deficiency in their patients by recommending dietary changes and/or dietary supplementation.

If you’re a patient, be sure to speak to your healthcare practitioner to determine if you’re at risk for vitamin B12 deficiency and if supplementation is right for you.

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  1. Green, R. (2017). Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood, 129(19), 2603-2611.
  2. Humphrey, L. L., Fu, R., Rogers, K, Freeman, M., & Helfand, M. (2008). Homocysteine level and coronary heart disease incidence: a systematic review and meta-analysis. Mayo Clinic Proceedings, 83(11),1203-1212.
  3. Langan, R. C., & Goodbred, A. (2017). Vitamin B12 deficiency: recognition and management. American Family Physician, 96(6), 384-389.
  4. Mahalle, N., Kulkarni, M. V., Garg, M. K., & Naik, S. S. (2013). Vitamin B12 deficiency and hyperhomocysteinemia as correlates of risk factors in Indian subjects with coronary artery disease. Journal of Cardiology, 61(4), 289-294.
  5. Nawaz, A., Khattak, N., Khan, M., Nangyal, H., Sabir, S., & Shakir, M. (2020). Deficiency of vitamin B12 and its relation with neurological disorders: a critical review. The Journal of Basic and Applied Zoology.81:10.
  6. National Institutes of Health Office of Dietary Supplements. (2021, April 6). Vitamin B12 Fact Sheet for Health Professionals.
  7. Obeid, R., Heil, S. G., Verhoeven, M., van den Heuvel, E., de Groot, L., & Eussen, S. (2019). Vitamin B12 Intake From Animal Foods, Biomarkers, and Health Aspects. Frontiers in nutrition, 6,93.
  8. O’Leary, F., & Samman, S. (2010). Vitamin B12 in health and disease. Nutrients, 2(3), 299–316.
  9. Pawlak, R. (2015). Is vitamin B12 deficiency a risk factor for cardiovascular disease in vegetarians? Am J Prev Med, 48(6), e11-26.
  10. Penninx, B. W., Guralnik, J. M., Ferrucci, L, Fried, L. P., Allen, R. H., & Stabler, S. P. (2000). Vitamin B12 deficiency and depression in physically disabled older women: epidemiologic evidence from the Women’s Health and Aging study. Am J Psychiatry. 157(5), 715-21.
  11. Shipton, M. J., & Thachil, J. (2015). Vitamin B12 deficiency – A 21st century perspective. Clinical medicine (London, England), 15(2), 145–150.
  12. Wolffenbuttel, B., Wouters, H., Heiner-Fokkema, M. R., & van der Klauw, M. M. (2019). The Many Faces of Cobalamin (Vitamin B12) Deficiency. Mayo Clinic Proceedings. Innovations, quality & outcomes, 3(2), 200–214.