Vitamin B12 Deficiency - Medicine With Heart

Are you deficient in B12? Could an undiagnosed B12 deficiency be part of the cause of your health issues?

Vitamin B12 is an essential vitamin that must be obtained through food. The body cannot make it. A B12 deficiency can affect vitality and health. While the official number of people who are deficient in B12 is not very high, sub-clinical deficiencies or generally low B12 levels can still produce symptoms.

In this blog on vitamin B12 deficiency, you will learn:

What is vitamin B12 and how common is a B12 deficiency?
What are the functions of B12?
What are the symptoms, causes and treatment for B12 deficiency?

What is Vitamin B12?

Vitamin B12 is a water-soluble vitamin found in animal products. It is in foods like meat, seafood, poultry, dairy products and eggs. Some processed foods (nutritional yeast, breakfast cereals, plant-based milks, vegan spreads, meat substitutes) are fortified with B12. Although we don’t love processed foods, this can be helpful for vegans and vegetarians to get B12 into their diets.

What are the Functions of Vitamin B12? (Ankar A, 2025)

Vitamin B12 is required to make and repair DNA.
It is involved in making red blood cells to carry oxygen throughout the body.
It is needed for normal nervous system function.
B12 helps convert food into energy which is crucial for brain function, mood and memory.
After it is absorbed, B12 is involved in making DNA, fatty acids and myelin.

What are the Symptoms of B12 Deficiency? (Patel H, 2025)

Low energy / persistent fatigue: Cells need B12 to function. Low B12 levels can decrease normal red blood cell production and impair oxygen delivery, causing fatigue.
Muscle weakness or cramps: B12 deficiency can affect nerve function, which can cause muscle cramps and weakness.
Pale or yellow skin: This may happen when there is a lack of healthy red blood cells in the body.
Headaches: Low vitamin B12 can increase chances of migraine. In research, people with higher B12 levels were 80% less likely to have a migraine headache compared with people with low B12 levels (Togha M, 2019).
Loss of appetite or weight loss
B12 deficiency anemia
Cognitive issues: Memory lapses, brain fog and issues with focus can occur, possibly as a result of nervous system issues like defective myelin synthesis and repair.
Neuropathy: a tingling sensation in hands or feet.
Low mood, anxiety, irritability, depression or mood changes: Low B12 can increase oxidative stress, DNA damage and cell death in the body and contribute to low mood (Esnafoglu E, 2020).
Impaired detoxification function
Hair loss
Susceptibility to infections
Heart palpitations, fast heart rate or shortness of breath
A painful, swollen, smooth tongue called glossitis or mouth ulcers
Balance problems can develop

Low B12 levels can affect brain health and cognitive decline (Beaudry-Richard A, 2025). In research, older otherwise healthy people with low B12 levels (yet still in the normal range) had neurological and cognitive deficiencies (Beaudry-Richard A, 2025). These older people with low B12 had slower cognitive and visual processing speeds in cognition tests, compared to peers with higher B12 (Beaudry-Richard A, 2025). Low B12 levels were associated with damage to the brain’s white matter. White matter is the nerve fibers that allow areas of the brain to communicate.

How Common is Vitamin B12 Deficiency?

Vitamin B12 deficiency occurs in approximately 2-3% of adults in the US (Patel H, 2025). Older data reflects 6% of the general population are B12 deficient (Langan RC, 2017).
Many more people may have sub optimal levels of B12 with accompanying (mild or not) symptoms.
B12 absorption from food decreases with age. Approx. 20% of people 60 years and older are deficient in vitamin B12 (Ankar A, 2025).
Approximately 1-2% cases of anemia are due to B12 deficiency (Ankar A, 2025).

How is a B12 Deficiency Identified?

Blood tests are used to measure B12 levels in the body.

The Reference Range for B12 in conventional medicine is 200-1100 pg/mL. A normal B12 range is from 300 pg/mL to 1100.
Borderline is 200–300 pg/mL and low or deficient B12 is <200 pg/mL.
In functional medicine, the optimal range is 800-1000 pg/mL.

An optimal B12 range of 800-1000 pg/mL supports energy, mental clarity, muscle tone, efficient detoxification and a healthy nervous system.

At the lower end of the range, around 300-500, a person is likely sub-clinically B12 deficient and has symptoms. Sub-clinical B12 deficiency can be a grey area. The serum B12 might be above the definition of a B12 deficiency. But the person will still have symptoms of deficiency, which may be mild or strong, yet be classified as having a healthy B12 level.

In functional medicine, we want to see a B12 level of 800-1000 pg/mL. This level avoids sub clinically deficient B12. If you have undiagnosed symptoms, especially of fatigue, we recommend testing B12 and coming to see us at our Medicine with Heart clinic.

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How is B12 Absorbed in the Body? The B12 absorption process is complex. Stomach acid is needed to release B12 from food proteins in the stomach. B12 then binds to different proteins and travels to the small intestine. In the small intestine it binds to intrinsic factor (IF). Intrinsic factor, secreted by parietal cells, is needed for B12 to be absorbed. The B12-IF bound complex moves to the last part of the small intestine. Here B12 can be absorbed into the cells. After absorption, B12 enters the bloodstream to be used for different functions. Extra B12 is stored in the liver. If liver stores get depleted a B12 deficiency develops. What Causes B12 Deficiency? Low B12 diet: A diet with no or low intake of animal products can cause a B12 deficiency. In fact, people on a strict vegan diet for 3 years or more were found to develop B12 deficiency (Ankar A, 2025). Poor B12 absorption: The absorption process for vitamin B12 is complex. It can be impaired by problems with digestion, intrinsic factor (IF) or parietal cells which secrete IF (Ankar A, 2025). Digestive issues or diseases that can impair B12 absorption include:

Crohn’s disease
Celiac disease
Chronic pancreatitis
SIBO (Small Intestinal Bacterial Overgrowth)
A tapeworm (Diphyllobothrium) from raw/undercooked fish or the parasite Giardia
Leaky gut or intestinal permeability
A Helicobacter pylori infection
Low stomach acid which is needed to absorb B12
Low intrinsic factor or parietal cell antibodies
Pernicious anemia or other autoimmune conditions

In people with normal intrinsic factor production, damage to the intestines can impair B12 absorption and cause deficiency. A surgical resection for Crohn’s disease, damage to the small intestine, inflammation from celiac disease or a tapeworm infection can all cause B12 deficiency (Ankar A, 2025). Parietal cell antibodies: Parietal cells in the stomach produce intrinsic factor which is needed for B12 absorption. The body may produce antibodies that attack and kill parietal cells. Parietal cell antibodies damage the parietal cells. If antibodies attack the parietal cells, then no IF is made and B12 cannot be absorbed without the intrinsic factor. Parietal cell antibodies are present in cases of chronic atrophic gastritis, gastric ulcers, Sjogren’s syndrome, pernicious anemia or other autoimmune conditions (Ankar A, 2025). Gastric atrophy (or atrophic gastritis) is chronic inflammation of the stomach lining, due to H pylori or autoimmune gastritis. Antibodies that destroy parietal cells or intrinsic factor or both are produced. Stomach acid and intrinsic factor cannot be produced which affects B12 absorption. Medication: Some quite common medications can lead to a B12 deficiency, especially if used long-term. These include Metformin for Type 2 Diabetes, Proton pump inhibitors (PPIs), for acid reflux, and other gastric acid–lowering drugs, or H2-receptor antagonists. Age: B12 deficiency is more common with older people. Stomach acid declines with age, making B12 absorption potentially more challenging in older people. How is a B12 Deficiency Diagnosed? Blood tests are used to diagnose B12 deficiency. Diagnosis may be more of an art than a science. A sub-clinical B12 deficiency can occur even though normal reference range levels are met. Testing B12 should be part of a routine health check, particularly with a relatively vague symptom like fatigue. Further testing may be required to determine the cause of B12 deficiency. If there is no clear cause of deficiency, tests for atrophic gastritis, Helicobacter pylori or autoantibodies associated with autoimmune gastritis should be done (Patel H, 2025). Folic acid deficiency can be confused with B12 deficiency. (Ankar A, 2025). How is B12 Deficiency Treated? The first-line treatment for a B12 deficiency is supplementing B12. With strict vegans, an oral supplement of B12 can boost B12 levels. If intrinsic factor is deficient due to pernicious anemia or gastric bypass surgery, oral B12 will not be absorbed because intrinsic factor is low. In this case, a non-oral B12 injection is recommended. B12 shots should be considered in cases of severe deficiency or neurological symptoms (Patel H, 2025). To treat the root cause of symptoms, it is important to understand why B12 is deficient. Tests for the different causes of B12 deficiency should be done to identify and treat the issue at the root. It is not recommended to prematurely take B12 if a deficiency or sub clinical deficiency is not identified. ************** If you have B12 deficient symptoms or are interested in optimizing your B12 levels, then get in touch with us at the Medicine with Heart clinic. We can help you to best manage and optimize your B12! *** Follow us for more info on vitamin B12 and B12 deficiency in our next blog! ***

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