Can B12 Deficiency Cause Extreme Tiredness and Fatigue?

December 6, 2025 •

3 min read

According to research, up to 20% of older adults in the US and UK have a vitamin B12 deficiency. This widespread issue can often be overlooked, with its primary symptom of extreme tiredness being easily mistaken for normal aging, stress, or other conditions.

Quick Summary

A B12 deficiency can cause profound tiredness and fatigue by hindering the production of healthy red blood cells, which carry oxygen throughout the body. The condition can manifest with various physical and neurological symptoms, and proper diagnosis is crucial for effective treatment.

Key Points

B12 and Energy: Vitamin B12 is essential for producing red blood cells, and a deficiency can cause extreme fatigue by hindering oxygen transport throughout the body.
Beyond Fatigue: In addition to tiredness, B12 deficiency symptoms include neurological issues like tingling and numbness, mood changes, memory problems, and a sore tongue.
Common Causes: Malabsorption due to conditions like pernicious anemia, gastritis, and certain medications (metformin, PPIs) is a common cause, alongside dietary intake issues in vegans and older adults.
Accurate Diagnosis: Diagnosis requires blood tests, including serum B12, MMA, and homocysteine, as symptoms can mimic other health problems.
Effective Treatment: Treatment ranges from oral supplements for mild cases to injections for severe deficiencies or malabsorption issues, effectively restoring energy levels.
Importance of Pro Guidance: It is crucial to consult a doctor for diagnosis and treatment to rule out other causes of fatigue and ensure proper therapy.

The Crucial Connection Between B12 and Extreme Tiredness

Yes, a vitamin B12 deficiency can absolutely cause extreme tiredness, or fatigue. Vitamin B12 is crucial for producing healthy red blood cells, which transport oxygen. When B12 is low, fewer healthy red blood cells are made, leading to megaloblastic anemia. This reduces oxygen transport, causing persistent fatigue.

Recognizing the Symptoms Beyond Fatigue

A B12 deficiency can cause physical, neurological, and psychological symptoms beyond fatigue, which can complicate diagnosis.

Common symptoms of B12 deficiency include:

Physical symptoms: Weakness, pale or yellowish skin, shortness of breath, a sore tongue, and potential changes in appetite or weight.
Neurological symptoms: Tingling or numbness (paresthesia), balance issues, memory problems, and vision changes.
Psychological symptoms: Irritability, mood swings, depression, or anxiety.

Causes of a Vitamin B12 Deficiency

Low B12 isn't solely dietary; absorption issues are common.

Reasons for low B12 levels include:

Dietary insufficiency: Common in vegans and vegetarians who don't supplement, as B12 is mainly in animal products.
Malabsorption issues: Often due to conditions like pernicious anemia (autoimmune attack preventing intrinsic factor production), gastritis (stomach lining inflammation), or digestive disorders like Crohn's or celiac disease.
Medical and Surgical Factors: Risk increases with age, gastric surgery, and certain medications like metformin or PPIs.

Diagnosing and Treating B12 Deficiency

Diagnosis involves blood tests like CBC and serum B12, with MMA and homocysteine levels potentially used for confirmation.

Treatment strategies vary:

Dietary Changes and Supplements: Oral or sublingual supplements can help if the cause is dietary.
Vitamin B12 Injections: Often needed for malabsorption issues like pernicious anemia, bypassing the digestive system.
Addressing Underlying Conditions: Treating the primary cause alongside B12 supplementation.

Comparison Table: B12 Deficiency vs. Iron Deficiency Fatigue

Fatigue has many causes. Here's a comparison of B12 and iron deficiency fatigue:


Feature	B12 Deficiency Anemia	Iron Deficiency Anemia
Primary Cause of Fatigue	Impaired red blood cell (RBC) formation.	Insufficient iron for hemoglobin.
Other Common Symptoms	Paresthesia, memory issues, mood changes, glossitis, balance problems.	Restless legs, brittle nails, chest pain, pica.
Onset	Develops slowly.	Can develop more quickly.
Diagnosis	Serum B12, MMA, homocysteine tests.	Ferritin, hemoglobin, iron studies.
Treatment Approach	B12 supplements (oral, injection), dietary changes.	Iron supplements (oral), dietary changes, address bleeding.

Conclusion: Seeking Professional Guidance is Key

B12 deficiency is a significant cause of extreme tiredness, stemming from poor red blood cell production and oxygen transport. It's often due to malabsorption, not just diet. Persistent fatigue with other symptoms warrants medical evaluation and blood tests to confirm the diagnosis and rule out other issues. Treatment, which can include supplements or injections, can restore energy and prevent long-term nerve damage. Always consult a doctor before starting treatment. More information can be found from sources like the National Heart, Lung, and Blood Institute.

When to See a Doctor

Consult a doctor for persistent fatigue, especially with other symptoms like tingling or memory issues. This is particularly important for vegans/vegetarians, those over 60, individuals on certain medications (metformin, PPIs), those with a history of gastric surgery, or those with autoimmune diseases like pernicious anemia. Injections can quickly improve energy, but persistent fatigue may indicate another issue.

Boosting Your B12 Levels Naturally

For those without absorption problems, increasing B12 through diet is helpful. Good sources include:

Examples of B12-rich foods:

Animal Sources: Organ meats, clams, salmon, beef, eggs, and dairy.
Fortified Sources (for vegans/vegetarians): Fortified cereals, plant-based milks, and nutritional yeast.

Check food labels for B12 content.

Frequently Asked Questions

For those with a confirmed B12 deficiency, injections deliver the vitamin directly into the bloodstream, bypassing absorption issues. Many people experience a noticeable improvement in their energy levels within a few days to a week, with more significant and sustained improvement occurring over several weeks or months.

Yes, B12 deficiency symptoms, particularly fatigue, can easily be mistaken for signs of aging, stress, depression, or other vitamin deficiencies like iron deficiency. This is why proper diagnosis through blood tests is crucial.

Yes, since vitamin B12 is found naturally almost exclusively in animal products, vegans and vegetarians are at a higher risk of deficiency if they don't supplement their diet with fortified foods or B12 supplements.

Pernicious anemia is an autoimmune condition where the body cannot produce a protein called intrinsic factor, which is necessary for B12 absorption in the stomach. Without intrinsic factor, dietary B12 cannot be properly absorbed, leading to a deficiency.

If left untreated for an extended period, B12 deficiency can lead to long-term nerve and brain damage, which may become permanent. Early diagnosis and treatment are essential to prevent irreversible neurological complications.

Diagnosis typically involves a complete blood count (CBC) to check for large red blood cells and a serum B12 test. Additional, more sensitive tests for methylmalonic acid (MMA) and homocysteine can also be used, especially in borderline cases.

Yes. Even if you consume animal products, you can still have a B12 deficiency due to malabsorption issues caused by conditions like pernicious anemia, gastritis, or certain medications. The body's ability to absorb B12 can also decrease with age.

If your B12 levels are already normal, a B12 shot is unlikely to provide a noticeable energy boost. The body will simply excrete the excess water-soluble vitamin. It's not a general pick-me-up but a medical treatment for a diagnosed deficiency.