What Health Problems Can Low B12 Cause? Understanding the Risks

October 11, 2025 •

3 min read

According to the National Institutes of Health, the symptoms of vitamin B12 deficiency can take several years to appear because the body can store large amounts. Therefore, many people with low B12 levels may be unaware of the developing health problems.

Quick Summary

Vitamin B12 deficiency can trigger a wide range of issues, affecting the nervous system, red blood cell production, and mental health. Left untreated, it can lead to severe and potentially irreversible conditions.

Key Points

Neurological damage: Low B12 can cause nerve damage, leading to tingling, numbness, memory loss, and difficulty walking.
Megaloblastic anemia: A lack of B12 impairs red blood cell production, resulting in fatigue, weakness, and pale skin.
Psychological symptoms: Deficiency is linked to mood changes, including depression, irritability, and in severe cases, paranoia and delusions.
Digestive and oral issues: Common symptoms include a sore or swollen tongue, mouth ulcers, constipation, and loss of appetite.
Irreversible damage: If left untreated, the neurological damage from B12 deficiency can become permanent.
Risk factors: Older adults, vegans, and people with gastrointestinal disorders are at higher risk of B12 deficiency.
Distinguishing from folate deficiency: Unlike folate, low B12 can cause severe neurological problems, and treating with only folate can mask a B12 deficiency and worsen nerve damage.

The Essential Role of Vitamin B12 in Your Body

Vitamin B12, also known as cobalamin, is crucial for maintaining healthy nerve cells and blood cells, as well as for the creation of DNA. A deficiency arises when the body either doesn't consume enough B12 or struggles to absorb it properly. Due to the body's capacity to store B12 in the liver, symptoms might not become apparent for several years.

Hematological Problems: Anemia and Beyond

Low B12 levels can lead to megaloblastic anemia, a condition where red blood cells become abnormally large and are unable to function effectively. This reduces the amount of oxygen delivered to tissues and organs, causing symptoms such as:

Fatigue and Weakness
Pale Skin and Heart Palpitations
Glossitis (a swollen, red tongue)
Digestive Issues like constipation or diarrhea

What is Pernicious Anemia?

Pernicious anemia is an autoimmune condition where the body attacks cells needed to absorb B12, requiring lifelong treatment with injections.

Neurological and Cognitive Damage

Vitamin B12 is essential for nerve function and the protective myelin sheath. A deficiency can result in various neurological issues:

Peripheral Neuropathy, causing tingling, numbness, or weakness in the limbs.
Cognitive Impairment, such as confusion and memory problems.
Vision Problems, including blurred vision.
Ataxia, affecting coordination and balance.

Psychological and Mental Health Manifestations

Low B12 can also impact mental health due to its role in neurotransmitter synthesis. Symptoms can include:

Depression and Irritability
More severe issues like paranoia or delusions in advanced cases.

Comparison of Low B12 and Low Folate Symptoms

Both low B12 and folate can cause megaloblastic anemia, but B12 deficiency uniquely affects neurological health. Treating B12 deficiency with only folate can worsen nerve damage. Additional information on the differences can be found on the {Link: NHLBI NIH website https://www.nhlbi.nih.gov/health/anemia/vitamin-b12-deficiency-anemia}.

Long-Term and Severe Complications

Untreated B12 deficiency can lead to severe issues, including potential permanent nerve damage and an increased risk of certain health conditions. More details are available on the {Link: NHLBI NIH website https://www.nhlbi.nih.gov/health/anemia/vitamin-b12-deficiency-anemia}.

Who is at Risk for Low B12?

Certain groups are at higher risk for B12 deficiency, such as vegans, older adults, and individuals with specific medical conditions or those taking certain medications. The {Link: NHLBI NIH website https://www.nhlbi.nih.gov/health/anemia/vitamin-b12-deficiency-anemia} provides a list of risk factors.

Conclusion: The Importance of Early Intervention

Low B12 can cause significant health problems affecting nerve function, blood production, and mental health. Symptoms may not appear for years, making early detection and treatment vital to prevent irreversible damage. High-risk individuals should be particularly aware of symptoms and get tested if concerns arise. Prompt diagnosis and treatment, often with supplementation or injections, can reverse many symptoms and prevent long-term issues. Consult a healthcare professional if you suspect a deficiency. For more information, the NHS website offers details on treatment.

Diagnosis and Treatment

Diagnosis involves blood tests to check B12 levels. Treatment varies; dietary deficiencies may be corrected with supplements, while malabsorption issues typically require B12 injections. Additional information can be found on the {Link: NHLBI NIH website https://www.nhlbi.nih.gov/health/anemia/vitamin-b12-deficiency-anemia}.

How to Prevent B12 Deficiency

Preventing B12 deficiency involves ensuring adequate intake. This can include consuming B12-rich foods, fortified foods, or considering supplements if at risk. Addressing underlying health issues is also important. The {Link: NHLBI NIH website https://www.nhlbi.nih.gov/health/anemia/vitamin-b12-deficiency-anemia} offers details on prevention strategies.

Frequently Asked Questions

Yes, if left untreated for a long time, the neurological damage caused by a severe B12 deficiency, such as nerve damage and cognitive impairment, can become permanent.

Early signs can be subtle and develop slowly over time. They often include fatigue, weakness, paleness, a sore tongue, and tingling sensations in the hands and feet.

While both can cause megaloblastic anemia, only a B12 deficiency typically causes severe neurological problems. Folic acid treatment can mask a B12 deficiency, allowing neurological damage to progress.

A doctor can diagnose B12 deficiency through blood tests. This typically includes a complete blood count (CBC) and testing the serum B12 levels. Sometimes, additional tests for methylmalonic acid (MMA) and homocysteine may be performed.

High-risk groups include older adults (over 75), people on strict vegan or vegetarian diets, and individuals with gastrointestinal disorders like Crohn's or pernicious anemia.

Yes, long-term use of certain medications, including some heartburn medicines (like proton pump inhibitors) and metformin for diabetes, can interfere with B12 absorption.

Treatment varies based on the cause. For dietary deficiencies, oral supplements or fortified foods may be enough. For malabsorption issues like pernicious anemia, vitamin B12 injections are often necessary.