Understanding What Are the Symptoms of a B12 Deficiency?

October 1, 2025 •

3 min read

The human body can store several years' worth of vitamin B12, which is why a deficiency can go unnoticed for an extended period. However, once these reserves are depleted, a wide range of signs and symptoms can appear, making it crucial to know what are the symptoms of a B12 deficiency?

Quick Summary

A vitamin B12 deficiency can manifest through a variety of issues, from chronic fatigue and weakness to neurological problems like numbness, tingling, and memory loss. Early recognition and treatment are key to preventing long-term complications.

Key Points

Diverse Symptom Presentation: B12 deficiency can cause a wide array of physical, neurological, and psychological symptoms, which may appear gradually and overlap with other conditions.
Delayed Onset: Due to the body's large storage capacity for vitamin B12 in the liver, a deficiency can go unnoticed for years until reserves are exhausted and symptoms begin to appear.
Risk Factors Vary: While dietary intake is a factor, particularly for vegans, most deficiencies are caused by absorption issues linked to autoimmune disorders (pernicious anemia), age, or gastrointestinal diseases.
Potential for Irreversible Nerve Damage: The neurological symptoms of a B12 deficiency, such as tingling, numbness, and memory loss, can become permanent if left untreated for a prolonged period.
Crucial for Red Blood Cells and Nerves: Vitamin B12 is essential for the production of healthy red blood cells and for maintaining the nervous system, with a deficiency compromising both functions.
Importance of Professional Diagnosis: Because symptoms can be general, a proper diagnosis requires blood tests to measure B12 levels and should always be confirmed by a healthcare provider.

The importance of vitamin B12

Vitamin B12, also known as cobalamin, is an essential water-soluble vitamin vital for red blood cell formation, nerve tissue health, and brain function. Since the body doesn't produce B12 and it's mainly in animal products, dietary intake is a common cause of deficiency, particularly for vegans. When B12 is insufficient, these crucial processes are disrupted, leading to health issues.

Common physical symptoms

A lack of B12 can result in megaloblastic anemia, where large, immature red blood cells are produced. This can cause several physical symptoms:

Chronic fatigue and weakness: Feeling tired due to insufficient oxygen reaching tissues.
Pale or yellowish skin (jaundice): Impaired red blood cell production can lead to jaundice.
Heart palpitations and shortness of breath: The heart works harder to compensate for reduced oxygen-carrying capacity.
Sore, red tongue (glossitis) and mouth ulcers: A swollen, painful tongue and frequent mouth sores are common.
Digestive issues: May include loss of appetite, weight loss, constipation, or diarrhea.
Difficulty with balance and walking (ataxia): Central nervous system damage can affect coordination.

Neurological and psychological signs

Untreated B12 deficiency can cause severe, potentially permanent neurological damage. Symptoms may include:

Pins and needles (paresthesia) and numbness: Nerve damage can cause tingling or prickling in the extremities, potentially progressing to loss of sensation.
Cognitive problems: Confusion, concentration issues, and memory loss can occur, and severe cases may link to dementia.
Mood changes and depression: Irritability, mood swings, and depression are associated with low B12.
Vision problems: Rare cases may involve disturbed vision or optic nerve damage.

B12 vs. folate deficiency: A comparison

B12 and folate deficiencies can both cause megaloblastic anemia and similar symptoms. However, B12 deficiency commonly includes neurological effects, while folate deficiency rarely causes nerve damage.


Feature	Vitamin B12 Deficiency	Folate Deficiency
Megaloblastic Anemia	Yes, common.	Yes, common.
Neurological Symptoms	Common; includes pins and needles, numbness, memory loss, and ataxia.	Rare; does not typically cause nerve damage.
Sore Tongue (Glossitis)	Yes, common.	Yes, common.
Fatigue	Yes, common.	Yes, common.
Digestive Issues	Yes, common.	Yes, common.
Supplement Effect	Can correct anemia and neurological symptoms if caught early.	Corrects anemia, but does not resolve neurological symptoms caused by B12 deficiency.

Causes and risk factors

Beyond diet, B12 deficiency is often due to malabsorption. Key causes include:

Pernicious anemia: An autoimmune condition where the immune system impairs intrinsic factor production, necessary for B12 absorption.
Dietary factors: Vegans and vegetarians are at higher risk.
Gastritis and reduced stomach acid: Age and chronic gastritis can hinder B12 extraction from food.
Digestive diseases: Conditions like Crohn's and celiac disease can damage absorption sites in the small intestine.
Surgery: Gastric surgeries can affect B12 absorption.
Medications: Some drugs, including metformin and certain antacids, can impact B12 levels.

How a B12 deficiency is diagnosed

Due to varied symptoms, B12 deficiency can be hard to diagnose. A doctor will review medical history, diet, and perform a physical exam. A blood test to check B12 levels is the primary diagnostic tool. Levels of methylmalonic acid (MMA) and homocysteine may also be measured.

Treatment options

Treatment depends on the cause and severity. Oral supplements may suffice for mild, diet-related cases. Injections are often needed for severe cases or absorption issues like pernicious anemia, potentially lifelong. Treatment can resolve symptoms, especially anemia, but long-term neurological damage may not be reversible.

Conclusion: Early detection is key

Recognizing the diverse symptoms of a B12 deficiency is vital for management. The gradual onset can delay diagnosis. High-risk individuals, such as the elderly and vegans, should consider screening. If symptoms are present, consult a healthcare professional for testing and treatment to prevent long-term complications. More information is available from authoritative health organizations like the National Institutes of Health (NIH).

Frequently Asked Questions

The most common early sign is often fatigue and a lack of energy. This is a result of megaloblastic anemia, where the body does not have enough healthy red blood cells to transport oxygen effectively.

Yes, a prolonged or severe vitamin B12 deficiency can damage the nerves and lead to neurological symptoms like numbness, tingling (paresthesia) in the hands and feet, muscle weakness, and issues with balance.

While both can cause megaloblastic anemia, B12 deficiency can also lead to nerve damage and related neurological symptoms. In contrast, folate deficiency rarely causes neurological problems.

Individuals over 75, people with autoimmune conditions like pernicious anemia, those with certain digestive diseases (e.g., Crohn's), and individuals following a vegan or strict vegetarian diet are at a higher risk.

Yes, cognitive issues such as memory loss, confusion, and difficulty thinking can be symptoms of a B12 deficiency. In advanced cases, it can contribute to a decline in mental abilities.

Diagnosis is typically made through a blood test that measures vitamin B12 levels. A doctor may also test for other compounds, such as methylmalonic acid (MMA), to help confirm the diagnosis.

Left untreated, it can lead to worsening symptoms, including severe nerve damage, vision problems, and a decline in cognitive function. Some neurological damage may become irreversible.