An Overview of Vitamin B12 Deficiency

This vitamin impacts many parts of your body

In This Article
Table of Contents

Vitamin B12 deficiency is a relatively common condition that can affect children and adults of all ages. Besides a low dietary intake, other factors that may cause this vitamin deficiency include gastric bypass surgery and diseases associated with gastrointestinal (GI) malabsorption.

Diagnosing vitamin B12 deficiency can be tricky because there are so many symptoms that mimic those of other health conditions. Blood tests, like a vitamin B12 test and complete blood count (CBC), are most helpful.

Treatment generally entails taking a vitamin B12 supplement or having an injection. If you have an illness that predisposes you to vitamin B12 deficiency, than managing the medical cause is also important.


The two main causes of vitamin B12 deficiency are inadequate intake and impaired absorption in the intestines.

Inadequate Intake

Vitamin B12 is found in animal proteins such as fish, meat, and milk, as well as some fortified cereals. Longstanding vegetarians or vegans who don't use supplements may develop a B12 deficiency due to inadequate nutritional intake of the vitamin. People who abuse alcohol and the elderly are also at risk for vitamin B12 deficiency.

Impaired Absorption

Since Vitamin B12 is absorbed in the gut through a complex process that relies on a protein called intrinsic factor, impaired intestinal absorption may also result in this vitamin deficiency.

Causes of impaired vitamin B12 gut absorption include:

  • Pernicious anemia, an autoimmune disorder in which antibodies attack the cells that release intrinsic factor
  • Inflammatory gastrointestinal (GI) disorders like Crohn's disease and celiac disease
  • Prolonged use of certain medications like metformin and proton pump inhibitors
  • Gastric bypass surgery, which involves resection of parts of the stomach and/or small intestine
  • GI resection surgery, which is a treatment for serious medical problems such as bowel obstruction or cancer


Due to the complex and vast role vitamin B12 plays in the body, there are many potential symptoms.


Vitamin B12 plays a role in the production of red blood cells (RBCs), which normally carry oxygen throughout the body. Since oxygen is a vital part of your body's energy production, when RBCs are defective (which occurs with vitamin B12 deficiency), anemia develops.

Symptoms of anemia include fatigue, dizziness, paleness, and a rapid heart rate.


Vitamin B12 is also a vital part of a healthy nervous system, and its absence causes slow degeneration of the nerves in the brain, spinal cord, and peripheral nerves. 

Neuropathy, which is impairment in nerve function, can cause tingling, numbness, weakness, and balance problems. Anemia can exacerbate weakness and imbalance.


Myelopathy, an impairment of spinal cord function, is produced when there is a deterioration of neurons in the posterior column of the spinal cord.

This results in muscle weakness and deficits in detecting light touch, vibration, and proprioception (position sense). Numbness and tingling are common effects of myelopathy as well.


Vitamin B12 deficiency may cause dementia, resulting in memory loss and cognitive decline , behavioral changes, and problems with self-care. With severe and chronic vitamin B12 deficiency, psychosis may develop.

Other Symptoms

Other symptoms and signs of vitamin B12 deficiency may include:

  • Low white blood cell count, which increases your risk for infection
  • Low platelet count, which increases your risk for bleeding
  • Headaches
  • Weight loss
  • Mood changes, especially depression
  • Behavioral changes
  • Walking problems
  • Loss or diminished sense of smell
  • Swollen tongue (called glossitis)

Symptoms of vitamin B12 deficiency typically develop gradually over the course of weeks or months and do not usually improve without treatment.


While the diagnosis of vitamin B12 may seem straightforward, it isn't always very obvious. This is because many of the common symptoms of vitamin B12 deficiency overlap with other health conditions.

Your medical team may consider a number of diagnoses to explain your symptoms—not just vitamin B12 deficiency.

History and Physical Examination

Besides a medical history, which may reveal symptoms like unexplained fatigue or numbness and tingling, your physical examination may identify signs of vitamin B12 deficiency.

For example, a weak, rapid pulse or pale fingers may be a sign of anemia. Diminished sensation in your feet and decreased reflexes can be a sign of neuropathy. Lastly, confusion or difficulty communicating are common signs of dementia and depression.

Laboratory Tests

Laboratory tests, specifically a complete blood count (CBC) and a vitamin B12 level, can confirm a diagnosis of vitamin B12 deficiency.

Moreover, often with vitamin B12 deficiency, a specific type of anemia called macrocytic anemia (not to be confused with pernicious anemia) can be identified with a blood smear. The RBCs appear large and may have a varied shape and size.

Imaging Tests and Specialized Tests

While certain imaging tests and nerve conduction studies (NCV) can be helpful in assessing the effects of vitamin B12 deficiency, they do not produce a specific pattern of results that corresponds with this deficiency.


Vitamin B12 deficiency can be managed with oral (by mouth) or intramuscular (IM) injections of the vitamin. If decreased absorption is among the causes of your vitamin B12 deficiency, then you may need to have an injection so that it will be absorbed directly into your body, rather than relying on your gastrointestinal (GI) system.

Recovery from B12 deficiency takes time and you may not experience any improvement during the first few months of treatment. Improvement may be gradual and may continue for up to 6 to 12 months.

If possible, the cause of the B12 deficiency should be addressed, especially if you have not had a surgical resection or do not know why you are low in this vitamin.

Depending on the reason for your vitamin deficiency, you may need to continue to use lifelong supplementation with vitamin B12 even after your symptoms improve.


It is possible that you may continue to suffer from lasting deficits of vitamin B12 deficiency, such as numbness, tingling, and weakness. These effects can impair your balance. Working with a physical or occupational therapist may help you optimize your abilities despite these lingering problems.

In addition, memory problems can improve as your vitamin B12 levels are corrected, but you may continue to experience some deficits in cognitive (thinking) skills for a long time. Cognitive rehabilitation and therapy is a challenging process, but it can help you maximize and improve your thinking and problem-solving skills.

A Word From Verywell

Vitamin B12 deficiency can be a fairly complicated diagnosis because the effects and symptoms are so varied. You might not experience sudden effects of the vitamin deficiency, instead, going through periods of gradual or intermittent declines in your vitamin B12 level—which results in subtle, or off and on symptoms.

If you have an inflammatory GI condition or if you have had a gastric resection, you may need to use a preventative treatment such as regularly scheduled vitamin B12 injections to avoid becoming deficient in this vitamin.

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  1. Ankar A, Kumar A. Vitamin B12 Deficiency (Cobalamin) [Updated 2019 Jan 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from:

  2. Lupoli R, Lembo E, Saldalamacchia G, Avola CK, Angrisani L, Capaldo B. Bariatric surgery and long-term nutritional issuesWorld J Diabetes. 2017;8(11):464–474. doi:10.4239/wjd.v8.i11.464

  3. Herrmann W, Obeid R. Causes and early diagnosis of vitamin B12 deficiencyDtsch Arztebl Int. 2008;105(40):680–685. doi:10.3238/arztebl.2008.0680

  4. Carmel R. How I treat cobalamin (vitamin B12) deficiencyBlood. 2008;112(6):2214–2221. doi:10.1182/blood-2008-03-040253

  5. Allen LH. Causes of vitamin B12 and folate deficiency. Food Nutr Bull. 2008;29(2 Suppl):S20-34.

  6. Langan RC, Goodbred AJ. Vitamin B12 Deficiency: Recognition and Management. Am Fam Physician. 2017;96(6):384-389.

  7. Ankar A, Kumar A. Vitamin B12 Deficiency (Cobalamin) [Updated 2019 Jan 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from:

  8. Stover PJ. Vitamin B12 and older adultsCurr Opin Clin Nutr Metab Care. 2010;13(1):24–27. doi:10.1097/MCO.0b013e328333d157

  9. Wolffenbuttel BHR, Wouters HJCM, Heiner-fokkema MR, Van der klauw MM. The Many Faces of Cobalamin (Vitamin B) Deficiency. Mayo Clin Proc Innov Qual Outcomes. 2019;3(2):200-214.

  10. Miller JW. Proton Pump Inhibitors, H2-Receptor Antagonists, Metformin, and Vitamin B-12 Deficiency: Clinical Implications. Adv Nutr. 2018;9(4):511S-518S.

  11. Huang S, Ma J, Zhu M, Ran Z. Status of serum vitamin B12 and folate in patients with inflammatory bowel disease in ChinaIntest Res. 2017;15(1):103–108. doi:10.5217/ir.2017.15.1.103

  12. O'Leary F, Samman S. Vitamin B12 in health and diseaseNutrients. 2010;2(3):299–316. doi:10.3390/nu2030299

  13. Pavlov CS, Damulin IV, Shulpekova YO, Andreev EA. Neurological disorders in vitamin B12 deficiency. Ter Arkh. 2019;91(4):122-129.

  14. Ekabe CJ, Kehbila J, Abanda MH, Kadia BM, Sama CB, Monekosso GL. Vitamin B12 deficiency neuropathy; a rare diagnosis in young adults: a case reportBMC Res Notes. 2017;10(1):72. Published 2017 Jan 28. doi:10.1186/s13104-017-2393-3

  15. Senol MG, Sonmez G, Ozdag F, Saracoglu M. Reversible myelopathy with vitamin B12 deficiency. Singapore Med J. 2008;49(11):e330-2.

  16. Baroni L, Bonetto C, Rizzo G, Bertola C, Caberlotto L, Bazzerla G. Association Between Cognitive Impairment and Vitamin B12, Folate, and Homocysteine Status in Elderly Adults: A Retrospective Study. J Alzheimers Dis. 2019 Jun 6. doi: 10.3233/JAD-190249

  17. Goebels N, Soyka M. Dementia associated with vitamin B(12) deficiency: presentation of two cases and review of the literature. J Neuropsychiatry Clin Neurosci. 2000;12(3):389-94.

  18. Langan RC, Goodbred AJ. Vitamin B12 Deficiency: Recognition and Management. Am Fam Physician. 2017 Sep 15;96(6):384-389.

  19. Wolffenbuttel BHR, Wouters HJCM, Heiner-Fokkema MR, van der Klauw MM. The Many Faces of Cobalamin (Vitamin B12) DeficiencyMayo Clin Proc Innov Qual Outcomes. 2019;3(2):200–214. Published 2019 May 27. doi:10.1016/j.mayocpiqo.2019.03.002

  20. Hannibal L, Lysne V, Bjørke-Monsen AL, et al. Biomarkers and Algorithms for the Diagnosis of Vitamin B12 Deficiency [published correction appears in Front Mol Biosci. 2017 Aug 08;4:53]. Front Mol Biosci. 2016;3:27. Published 2016 Jun 27. doi:10.3389/fmolb.2016.00027

  21. Berg RL, Shaw GR. Laboratory evaluation for vitamin B12 deficiency: the case for cascade testingClin Med Res. 2013;11(1):7–15. doi:10.3121/cmr.2012.1112

  22. Nagao T, Hirokawa M. Diagnosis and treatment of macrocytic anemias in adultsJ Gen Fam Med. 2017;18(5):200–204. Published 2017 Apr 13. doi:10.1002/jgf2.31

  23. Fava E, Kofler M, Saltuari L. Reversible cutaneous silent period abnormalities in vitamin B12 deficiency: A case reportClin Neurophysiol Pract. 2019;4:128–132. Published 2019 May 31. doi:10.1016/j.cnp.2019.05.002

  24. Chan CQ, Low LL, Lee KH. Oral Vitamin B12 Replacement for the Treatment of Pernicious AnemiaFront Med (Lausanne). 2016;3:38. Published 2016 Aug 23. doi:10.3389/fmed.2016.00038

  25. Stover PJ. Vitamin B12 and older adultsCurr Opin Clin Nutr Metab Care. 2010;13(1):24–27. doi:10.1097/MCO.0b013e328333d157

  26. Moore E, Mander A, Ames D, Carne R, Sanders K, Watters D. Cognitive impairment and vitamin B12: a review. Int Psychogeriatr. 2012;24(4):541-56.