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Do you have a B12 deficiency?

Last Modified: February 01, 2023

Family Medicine

B12 deficiency

Vitamin and mineral deficiencies can lead to a host of health problems, but how do you know if you’re lacking one of these essential micronutrients? Drew Hosier, DO, PPG – Family Medicine & Internal Medicine, explains what vitamin B12 is, the common signs of a deficiency and when you should seek assistance from a healthcare provider.

Vitamin B12, also known as cobalamin, occurs naturally in animal-based food products such as meat, eggs or dairy. It’s also a common supplement in fortified foods like breakfast cereals, plant-based milk and bread. It is an essential micronutrient necessary for turning food into energy within the body. When the body absorbs B12 from food in its natural state, it gets converted in the stomach for many metabolic functions. When taken as a supplement, B12 gets absorbed as the already converted form. In either case, it supports the immune system, develops brain and nerve cells, and makes new red blood cells with the help of folic acid (another B vitamin).  

Who’s at risk of a deficiency?

Vitamin B12 deficiency affects 1-2% of the general population and is typically attributed to one of two scenarios. The first is when someone isn’t consuming enough B12 in their diet. This is usually the case for elderly populations, those following a vegetarian or vegan diet, and people with disordered eating or chronic diseases that lead to malnutrition.

The second is when your body isn’t absorbing enough vitamin B12 properly. This is most common in people with a history of weight loss surgery, gastric surgery, Crohn’s disease (due to less intake and decreased stomach acid to convert B12 into a useable form), autoimmune conditions, chronic stomach inflammation from a bacterial infection like H. pylori and long-term use of medicines that limit stomach acid such as proton pump inhibitors, H2 blockers and/or metformin.

Common signs and symptoms

Most B12 deficiencies aren’t clinically evident, but as the condition progresses, certain symptoms could develop. The most common warning signs are:

  • Fatigue
  • Dizziness
  • Weakness
  • Nausea
  • Vomiting
  • Diarrhea
  • Pale or yellowish skin
  • Mood changes (depressed or irritable)
  • Sore mouth and/or a swollen tongue
  • Numbness and tingling in the extremities
  • Difficulty walking or speaking like normal
  • Memory impairment and/or forgetfulness
  • Changes in cognition
Diagnosis and treatment

Because symptoms are not always present, providers usually choose a variety of blood tests to check for a B12 deficiency. These tests can help doctors determine if someone has a primary deficiency (not enough vitamin intake) or a secondary deficiency (due to an underlying disorder).

In most cases, the outlook for someone with a B12 deficiency is excellent, though the speed of progress can vary. Once someone begins treatment with either dietary or supplemental sources, it can take weeks to months to replenish their B12 levels and resolve any symptoms resulting from the deficiency.

Additionally, a common occurrence regarding B12 deficiencies is over-supplementation. While efforts are well-intentioned, many people overestimate their risk or underestimate their supplemental doses, which can cause added symptoms such as headaches, nausea, vomiting, diarrhea, itching and skin rashes. For this reason, it’s always good practice to review your supplement regimen with your primary care provider or medical team at every visit to avoid any adverse effects.


Someone can prevent a B12 deficiency by eating a well-balanced diet or through supplementation if dietary deficiencies or absorptive conditions limit the body from getting what it needs from food and beverages alone. If supplementation is necessary, your provider may suggest a simple oral supplement available over the counter. At times, particularly in situations with individuals who have absorption issues, B12 supplementation may occur through routine injections.

When to seek medical assistance from a healthcare provider

If you are experiencing symptoms or are at risk of developing a vitamin B12 deficiency, you should speak with your primary care provider. They may ask you to take a blood test to measure and monitor your B12 levels. If you currently have a B12 deficiency and are experiencing new or concerning symptoms, you should reach out to your physician or seek immediate emergency medical care.

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