Vitamin B12 deficiency is common and underdiagnosed, even though excess B12 is stored in the liver. Vitamin B12 is found mainly in animal products, fortified breakfast cereals, and nutritional yeast. People who take certain medicines, eat a vegan or vegetarian diet, or have had stomach problems in the past may need to supplement their vitamin B12 (Ankar, 2022).

Human physiology is complex. While scientists have identified several roles for vitamin B12 in the body, there are likely hundreds of others that have not been identified or are attributed to another vitamin or mineral alone. Imagine the most complex spider web you can think of. If you had to write a chemical reaction on each thread, you wouldn’t begin to approximate all the chemical reactions occurring in your body. 

Helps Maintain Energy Levels

Red blood cells carry oxygen to your body cells and remove carbon dioxide. When red blood cells aren’t functioning properly, your body tissues may not achieve optimal oxygen levels, which can cause fatigue. 

Healthy red blood cells have a biconcave disc shape. This shape holds the most hemoglobin possible and provides the most surface area for oxygen and carbon dioxide to move through. Healthy red blood cells are flexible and fold as they move through the smallest blood vessels. 

If a person does not have enough vitamin B12, their red blood cells become larger and more oval because vitamin B12 affects how DNA and RNA work in their cells. When DNA and RNA production lags, it causes changes in red blood cell composition. These larger cells cannot move as easily from the bone marrow, where they are produced, to the blood vessels, where they circulate. This is called megaloblastic anemia (Hariz, 2022). 

Many of the symptoms associated with vitamin B12 deficiency are due to anemia. Symptoms associated with anemia include:

• Fatigue
• Pale skin
• Cold fingers and toes
• Weakness
• Dizziness
• Shortness of breath
• Palpitation
• Sore, glossy tongue

Involved In Heart Health

Vitamin B12 is involved in several key chemical reactions, including:

• Conversion of homocysteine to methionine

Methionine is needed to make S-adenosylmethionine, which is a methyl donor that can be used in almost 100 different chemical reactions. Some of these reactions are involved in DNA, RNA, and protein metabolism. 

Low vitamin B12 levels are associated with high homocysteine levels, which can have effects throughout the body (Clarke 2003). High levels of homocysteine are linked to early-onset heart disease. Low vitamin B12 and folate levels and kidney disease cause high homocysteine (Vizzardi 2009). Randomized clinical trials have shown that vitamin B12 and folate supplements can lower homocysteine levels but not cardiovascular disease risk (NIH 2022). 

• Conversion of methylmalonyl CoA to succinyl coenzyme A

The conversion of methylmalonyl CoA to succinyl coenzyme A is essential in metabolizing fatty acids and proteins for energy. Fats and proteins are broken down to produce methylmalonyl CoA, which is then converted to succinyl-CoA, which enters the citric acid cycle. This important cycle is found in the mitochondria and is used to produce energy for the cell. 

Helps Stabilize Mood 

SAM-e (S-adenosyl methionine) is made with the help of both vitamin B12 and folic acid. SAM donates methyl groups, which are essential for healthy brain function. Homocysteine is converted to methionine, which is used to form SAM. Vitamin B12 deficiency slows this conversion, resulting in increased homocysteine. Increased homocysteine is a marker for vitamin B12 and folate deficiency. 

Homocysteine levels are increased in people with depression. Based on the results of clinical trials, researchers suggested that taking supplements of folic acid and vitamin B12 could help improve depressive symptoms (Coppen, 2005). 

Vitamin B12 is also involved in producing serotonin, a chemical messenger in the brain that modulates mood. More research is needed to understand the relationship between vitamin B12, serotonin, and mood (Almeida, 2015).

May Improve Cognitive Function

Elevated homocysteine levels are associated with an increased incidence of Alzheimer’s disease and dementia. High homocysteine levels may reduce blood flow and oxygen to brain cells, increase protein tangles in the brain, and inhibit methylation reactions. But it is not clear if restoring healthy levels of vitamin B12 with a supplement can improve cognitive function because the research studies that are available are not well-designed (Smith, 2016). 

A systematic review of 43 clinical trials found that low vitamin B12 levels are associated with cognitive impairment and dementia, and a small subset of these are reversible with vitamin B12 replacement. Researchers found that vitamin B12 supplementation did not improve cognition in people with healthy B12 levels (Moore, 2012). 

Scientists use several different kinds of studies. The ideal study is a randomized, controlled clinical trial. Unfortunately, these kinds of studies cannot be used to investigate the effects of vitamin B12 deficiency because researchers would need to make some people vitamin B12 deficient and then see the effects on their health. So instead, researchers observe the effect of vitamin B12 deficiency on people who are already diagnosed with low B12. Observational studies are viewed critically because they are open to bias and statistical interpretation. 

May Reduce Cancer Risk

Researchers do not fully understand the relationship between vitamin B12 levels and cancer risk. Some studies show an increased risk of cancer with vitamin B12 deficiency, especially for stomach cancer (Miranti 2017), but this is not consistent across all studies, and some even showed opposite results (NIH 2022). 

May Reduce Pain

Vitamin B12 is essential for proper nerve function. A lack of vitamin B12 can cause paresthesias and nerve pain. Paresthesias are tingling or pins-and-needles sensations in the fingers and toes. Restoring vitamin B12 levels may help reduce pain and these uncomfortable sensations. 

May Boost Metabolism

Vitamin B12 is involved in converting the energy stored in food into a form your body cells can use. In an extensive study, researchers in the US found an inverse relationship between vitamin B12 deficiency and obesity. Further research will be needed to determine whether this is a causative relationship or if other factors contribute to it (Sun 2019, Boachie 2020).

Which Foods Are Highest In Vitamin B12?

Only bacteria can produce vitamin B12. It is found in animal products such as meat, poultry, fish, dairy, and eggs. According to a US national survey, the average dietary intake of vitamin B12 is 5.4 μg/day for adult men and 3.4 μg/day for adult women (Dror 2012).

Foods high in vitamin B12 include:

• Organ meats
• Clams
• Sardines
• Crab
• Mackerel
• Beef
• Fortified cereals
• Nutritional yeast

Are There Any Health Risks From Excessive Vitamin B12?

According to the National Institutes of Health, the Food and Nutrition Board (FNB) did not establish an upper limit for vitamin B12 because it has low toxicity and is considered safe, even at large doses (NIH 2022).

Restoring your vitamin B12 levels to a healthy range has many health advantages. If you have a health condition, dietary needs, or are taking a medication that is associated with low vitamin B12, talk to your healthcare provider about your symptoms to learn whether vitamin B12 deficiency may be the cause.

Looking to get vitamin B12? See how Invigor Medical can help today!

DISCLAIMER

While we strive to always provide accurate, current, and safe advice in all of our articles and guides, it’s important to stress that they are no substitute for medical advice from a doctor or healthcare provider. You should always consult a practicing professional who can diagnose your specific case. The content we’ve included in this guide is merely meant to be informational and does not constitute medical advice.

References:

Almeida OP, Ford AH, Flicker L. Systematic review and meta-analysis of randomized placebo-controlled trials of folate and vitamin B12 for depression. Int Psychogeriatr. May 2015;27(5):727-37. doi:10.1017/s1041610215000046

Ankar A, Kumar A. Vitamin B12 Deficiency. [Updated 2022 Aug 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Available from: https://www.ncbi.nlm.nih.gov/books/NBK441923/

Boachie J, Adaikalakoteswari A, Samavat J, Saravanan P. Low Vitamin B12 and Lipid Metabolism: Evidence from Pre-Clinical and Clinical Studies. Nutrients. Jun 29 2020;12(7)doi:10.3390/nu12071925

Clarke R, Refsum H, Birks J, et al. Screening for vitamin B-12 and folate deficiency in older persons. The American Journal of Clinical Nutrition. 2003;77(5):1241-1247. doi:10.1093/ajcn/77.5.1241

Coppen A, Bolander-Gouaille C. Treatment of depression: time to consider folic acid and vitamin B12. J Psychopharmacol. 2005 Jan;19(1):59-65. doi: 10.1177/0269881105048899. PMID: 15671130.

Dror DK, Allen LH. Interventions with vitamins B6, B12 and C in pregnancy. Paediatr Perinat Epidemiol. 2012;26 Suppl 1:55-74.

Hariz A, Bhattacharya PT. Megaloblastic Anemia. [Updated 2022 Sep 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Available from: https://www.ncbi.nlm.nih.gov/books/NBK537254/

Miranti EH, Stolzenberg-Solomon R, Weinstein SJ, Selhub J, Männistö S, Taylor PR, Freedman ND, Albanes D, Abnet CC, Murphy G. Low vitamin B12 increases risk of gastric cancer: A prospective study of one-carbon metabolism nutrients and risk of upper gastrointestinal tract cancer. Int J Cancer. 2017 Sep 15;141(6):1120-1129. doi: 10.1002/ijc.30809. Epub 2017 Jun 21. PMID: 28568053; PMCID: PMC5550828.

Moore E, Mander A, Ames D, Carne R, Sanders K, Watters D. Cognitive impairment and vitamin B12: a review. Int Psychogeriatr. 2012 Apr;24(4):541-56. doi: 10.1017/S1041610211002511. Epub 2012 Jan 6. PMID: 22221769.

Smith AD, Refsum H. Homocysteine, B Vitamins, and Cognitive Impairment. Annu Rev Nutr. 2016 Jul 17;36:211-39. doi: 10.1146/annurev-nutr-071715-050947. PMID: 27431367.

Sun Y, Sun M, Liu B, et al. Inverse Association Between Serum Vitamin B12 Concentration and Obesity Among Adults in the United States. Front Endocrinol (Lausanne). 2019;10:414. doi:10.3389/fendo.2019.00414

Vizzardi E, Bonadei I, Zanini G, Frattini S, Fiorina C, Raddino R, Dei Cas L. Homocysteine and heart failure: an overview. Recent Pat Cardiovasc Drug Discov. 2009 Jan;4(1):15-21. doi: 10.2174/157489009787259991. PMID: 19149701.

Vitamin B12. (2022). NIH.gov. Retrieved November 29, 2022, from https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/

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