How to Tell If You Need More B12

by JJ Virgin on November 28, 2023

Many years ago, I worked with a 45-year-old client, whom we’ll call Sarah. Despite getting adequate sleep, she constantly felt drained of energy. She initially dismissed the tingling sensation in her fingers and toes as a symptom of stress. 

Sarah’s mood had become increasingly unpredictable, often feeling irritable. Alongside a noticeably paler complexion, she frequently grappled with brain fog and found concentrating for even short amounts of time challenging. The tipping point was when she missed an important meeting with her teenage daughter’s track coach. 

While Sarah suspected perimenopause, her estrogen and other hormone levels were in the normal range. Instead, her blood tests showed a vitamin B12 deficiency. A follow-up lab test showed her deficiency stemmed from pernicious anemia

With this condition, your body mistakenly attacks its own stomach cells. This makes absorbing B12 harder. When you eat, your stomach produces a protective substance (called intrinsic factor) that helps vitamin B12 safely pass through its acid. 

Without the protection of intrinsic factor, vitamin B12 might not make it through the harsh environment of the gut, leading to potential deficiencies. While Sarah’s case was extreme, it highlights how being deficient in one vitamin can have widespread ramifications. 

What Is Vitamin B12 Important For?  

Vitamin B12, also known as cobalamin, is a vital nutrient your body requires to function properly. Found mainly in foods from animals like meat, fish, and dairy, B12 is essential for: 

  1. Helping convert the food you eat into energy1 
  1. Maintaining the protective covering around nerve fibers, which reduces the risk of neurological disorders like dementia2 
  1. Supporting red blood cell formation, which carries oxygen around the body3 
  1. Aiding in DNA synthesis (providing your body the right instructions to grow, repair, reproduce, and stay healthy)4 
  1. Protecting your heart5 
  1. Brain health and reducing cognitive decline6 
  1. Positively influencing mood-regulating chemicals in the brain7 
  1. Helping prevent osteoporosis with calcium and vitamin D8 
  1. Promoting healthy skin9 

What Causes B12 Deficiencies? 

Because most foods that provide vitamin B12 are animal sources, vegetarians and vegans have an increased risk of developing B12 deficiencies due to the absence of these sources in their diets. 

Other conditions that can lead to B12 deficiencies include: 

  • Medical conditions, such as pernicious anemia, celiac disease, Crohn’s disease, and atrophic gastritis 
  • Age (you don’t absorb B12 as well as you get older) 
  • Overconsuming alcohol 
  • Parasitic infections 
  • Genetic factors 
  • HIV/AIDS and chronic kidney disease 
  • Medications including proton pump inhibitors (PPIs), Metformin, and antacids10-11 

What Are the Symptoms of Low B12 Levels? 

Being low or deficient in vitamin B12 can significantly affect your health and well-being. Some potential repercussions of deficiencies include: 

  • Fatigue, weakness, pallor (signifying a type of anemia)12 
  • Tingling, numbness, difficulty walking, balance problems, memory impairment13 
  • Cognitive decline, and increased risk of neurodegenerative disorders1415 
  • Mood disorders, including depression and anxiety16 
  • Cardiovascular issues like elevated homocysteine levels and heart problems, including an increased risk of heart attack and atherosclerosis (a condition where fatty deposits or plaques build up in your arteries.17 
  • Gastrointestinal issues, including gastritis or inflammation of the stomach lining18 
  • Difficulty absorbing nutrients19-20 
  • Pregnancy risks, including neural tube defects21 

How Do I Know if I’m Low in Vitamin B12? 

My motto has always been test, don’t guess. Symptoms of vitamin B12 deficiencies can overlap with other deficiencies, and blood tests can detect whether you’re deficient in this vitamin. Talk with your healthcare practitioner about the following tests:  

  • Serum Vitamin B12 Test: Most doctors use this blood test to check your B12 levels initially. This measures the amount of vitamin B12 in your bloodstream. 
  • Complete Blood Count (CBC): This test can help identify if you have anemia, often associated with B12 deficiency. A CBC measures various components of your blood, including red blood cells and hemoglobin. 
  • Methylmalonic Acid (MMA) Test: Elevated levels of MMA in your blood can be a more sensitive indicator of B12 deficiency than a serum B12 test. MMA levels rise when B12 is insufficient to convert it into a usable form. 
  • Homocysteine Test: High levels of homocysteine can indicate a B12 deficiency. B12 is essential for converting homocysteine into the amino acid methionine. B12 deficiencies may impair this conversion process, leading to high levels of homocysteine and increasing your risk of heart problems. 
  • Intrinsic Factor Antibody Test: If your doctor suspects pernicious anemia, they may order an intrinsic factor antibody test. Positive results suggest the presence of these antibodies, which can help confirm the diagnosis. 

Nutrient Panel Testing from YourLabwork+ looks at vitamin B12 and other critical nutrient levels, including vitamin D, omega-3 fatty acids, and magnesium. Learn more about the test here. 

How to Fix a Vitamin B12 Deficiency 

Your healthcare practitioner may recommend supplements to replenish B12 levels based on your condition and the severity of your deficiency. You’ll find vitamin B12 in two forms: cyanocobalamin and methylcobalamin. Cyanocobalamin is the synthetic form of vitamin B12.  

Most B12 supplements use this form because of its stability and cost-effectiveness. However, your liver has to convert that B12 into its active form, methylcobalamin. Research shows that your body better absorbs and retains methylcobalamin than with cyanocobalamin. 22 

My client, Sarah, worked with a functional medicine doctor, who used vitamin B12 injections until her levels were back to normal. These injections bypass the need for intrinsic factor by delivering a direct and high dose of this vitamin into the bloodstream. Her doctor also addressed her underlying gut issues, which included small intestinal bacterial overgrowth (SIBO). A custom-designed autoimmune diet helped manage her pernicious anemia as well.  

As her gut began to heal and they found ways to keep her autoimmune condition at bay, Sarah’s doctor found that high-dose oral vitamin B12 supplements worked just as well as injections.  

She also increased her intake of foods rich in vitamin B12, including:  

  • Beef, pork, lamb, and poultry 
  • Wild-caught fatty fish like salmon, trout, and mackerel 
  • Pastured eggs (if you aren’t intolerant) 

While B12 alone serves many functions I’ve discussed, this vitamin also relies on other B vitamins to carry out these functions efficiently. Processes such as nervous system support and energy production depend on a symphony of B vitamins.  

Some people may benefit from targeted doses of vitamin B12, but a B-complex supplement provides optimal amounts of vitamin B12 along with other B vitamins for broader support for your well-being. 


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  1. Calderón-Ospina CA, Nava-Mesa MO. B Vitamins in the nervous system: Current knowledge of the biochemical modes of action and synergies of thiamine, pyridoxine, and cobalamin. CNS Neurosci Ther. 2020 Jan;26(1):5-13. doi: 10.1111/cns.13207. Epub 2019 Sep 6. PMID: 31490017; PMCID: PMC6930825. 
  1. Hariz A, Bhattacharya PT. Megaloblastic Anemia. [Updated 2023 Apr 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: 
  1. Al Amin ASM, Gupta V. Vitamin B12 (Cobalamin) [Updated 2023 Jul 16]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: 
  1. Kataria N, Yadav P, Kumar R, Kumar N, Singh M, Kant R, Kalyani V. Effect of Vitamin B6, B9, and B12 Supplementation on Homocysteine Level and Cardiovascular Outcomes in Stroke Patients: A Meta-Analysis of Randomized Controlled Trials. Cureus. 2021 May 11;13(5):e14958. doi: 10.7759/cureus.14958. PMID: 34123655; PMCID: PMC8191525. 
  1. Jatoi S, Hafeez A, Riaz SU, Ali A, Ghauri MI, Zehra M. Low Vitamin B12 Levels: An Underestimated Cause Of Minimal Cognitive Impairment And Dementia. Cureus. 2020 Feb 13;12(2):e6976. doi: 10.7759/cureus.6976. PMID: 32206454; PMCID: PMC7077099. 
  1. Sangle P, Sandhu O, Aftab Z, Anthony AT, Khan S. Vitamin B12 Supplementation: Preventing Onset and Improving Prognosis of Depression. Cureus. 2020 Oct 26;12(10):e11169. doi: 10.7759/cureus.11169. PMID: 33251075; PMCID: PMC7688056. 
  1. Dai Z, Koh WP. B-vitamins and bone health–a review of the current evidence. Nutrients. 2015 May 7;7(5):3322-46. doi: 10.3390/nu7053322. PMID: 25961321; PMCID: PMC4446754. 
  1. Brescoll J, Daveluy S. A review of vitamin B12 in dermatology. Am J Clin Dermatol. 2015 Feb;16(1):27-33. doi: 10.1007/s40257-014-0107-3. PMID: 25559140. 
  1. National Institutes of Health: Vitamin B12 
  1. Medical News Today: Long-term antacid use linked to vitamin B12 deficiency 
  1. Hariz A, Bhattacharya PT. Megaloblastic Anemia. 2023 Apr 3. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan–. PMID: 30725939. 
  1. Harvard Health: Vitamin B12 deficiency can be sneaky and harmful 
  1. Cambridge University Press & Assessment: Cognitive impairment and vitamin B12: a review 
  1. Jatoi S, Hafeez A, Riaz SU, Ali A, Ghauri MI, Zehra M. Low Vitamin B12 Levels: An Underestimated Cause Of Minimal Cognitive Impairment And Dementia. Cureus. 2020 Feb 13;12(2):e6976. doi: 10.7759/cureus.6976. PMID: 32206454; PMCID: PMC7077099. 
  1. Psych Central: B12 and Depression: What’s the Connection? 
  1. Harvard T.H. Chan School of Public Health: Vitamin B12 | The Nutrition Source 
  1. Karanth VK, Karanth L, Karanth TK, Karanth SK, Bekur R. A novel screening tool (Karanth’s test) for vitamin B12 deficiency: a pilot study. BMC Res Notes. 2015 Dec 12;8:778. doi: 10.1186/s13104-015-1744-1. PMID: 26652288; PMCID: PMC4677048. 
  1. Cleveland Clinic: Pernicious Anemia 
  1. Vaqar S, Shackelford K. Pernicious Anemia. [Updated 2023 May 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: 
  1. Finkelstein JL, Layden AJ, Stover PJ. Vitamin B-12 and Perinatal Health. Adv Nutr. 2015 Sep 15;6(5):552-63. doi: 10.3945/an.115.008201. PMID: 26374177; PMCID: PMC4561829. 
  1. Paul C, Brady DM. Comparative Bioavailability and Utilization of Particular Forms of B12 Supplements With Potential to Mitigate B12-related Genetic Polymorphisms. Integr Med (Encinitas). 2017 Feb;16(1):42-49. PMID: 28223907; PMCID: PMC5312744. 

The views in this blog by JJ Virgin should never be used as a substitute for professional medical advice. Please work with a healthcare practitioner concerning any medical problem or concern. The information here is not intended to diagnose, treat, or prevent any disease or condition. Statements contained here have not been evaluated by the Food and Drug Administration. 

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. 

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