What will low vitamin B12 do to your body?

October 6, 2025 •

3 min read

According to research, a severe vitamin B12 deficiency can damage nerves, causing symptoms that range from tingling in the hands and feet to confusion and memory problems. A lack of this essential nutrient can affect multiple body systems, leading to a wide array of physical, neurological, and psychological issues if left untreated.

Quick Summary

A deficiency in vitamin B12 can cause megaloblastic anemia, fatigue, and nerve damage. It also impacts mental function, mood, and cognitive abilities. Severe, long-term deficiencies can result in irreversible complications affecting the heart and spinal cord.

Key Points

Megaloblastic Anemia: A B12 deficiency disrupts red blood cell production, leading to fatigue, weakness, and paleness due to a lack of oxygen.
Neurological Damage: A severe lack of B12 can damage nerves, causing numbness, tingling, difficulty walking, and vision problems that can become permanent.
Cognitive and Psychological Impact: Memory loss, confusion, depression, irritability, and even psychosis can result from low B12 affecting the brain and nervous system.
Heart-Related Complications: Anemia strains the cardiovascular system, potentially leading to a rapid heart rate and, in severe cases, heart failure.
High-Risk Groups: Strict vegans, older adults, and individuals with malabsorption disorders like pernicious anemia are particularly vulnerable to low vitamin B12.
Importance of Early Intervention: Timely diagnosis and treatment are crucial for reversing symptoms and preventing irreversible damage to the nervous system and heart.

The Core Functions of Vitamin B12

Vitamin B12, also known as cobalamin, is crucial for red blood cell formation, DNA synthesis, and nerve cell maintenance. Since the body cannot produce B12, it must be obtained from the diet, primarily through animal products, or from supplements. Vegetarians and vegans often need fortified foods or supplements to ensure adequate intake. A deficiency disrupts these processes, leading to health problems. Symptoms may develop gradually and can be misdiagnosed due to their varied nature. Early treatment is vital, as severe deficiency can cause permanent nerve damage.

Physical Manifestations of Low Vitamin B12

A common effect of low B12 is megaloblastic anemia, which results in abnormally large, dysfunctional red blood cells. This reduces oxygen delivery and causes symptoms such as:

Chronic Fatigue and Weakness: Due to insufficient healthy red blood cells.
Pale or Yellowish Skin: Caused by reduced red blood cells and potential cell destruction.
Glossitis and Mouth Ulcers: A sore, smooth, and swollen tongue, sometimes with mouth sores.
Gastrointestinal Distress: Including nausea, diarrhea, decreased appetite, and weight loss.
Rapid Heart Rate and Shortness of Breath: In severe anemia, the heart works harder to pump oxygen, leading to these symptoms.

Neurological and Cognitive Problems

B12 is essential for a healthy nervous system, and deficiency can lead to nerve damage. Symptoms include:

Numbness and Tingling: A common nerve-related symptom, often in the extremities.
Difficulty with Balance and Coordination: Severe deficiency can impair physical coordination.
Vision Disturbances: While less frequent, vision problems can occur.
Memory Loss and Cognitive Impairment: Affecting thinking and judgment, potentially mimicking dementia.
Psychological Changes: Such as depression, irritability, paranoia, and delusions.

Comparison of B12 Deficiency Symptoms by Severity


Feature	Mild Deficiency	Moderate to Severe Deficiency
Energy Levels	General fatigue, lack of energy.	Extreme tiredness, pronounced weakness.
Skin and Tongue	Normal or slight pallor; occasional mouth sores.	Pale yellow tinge to skin; sore, red, and swollen tongue (glossitis).
Neurological Sensation	Mild, intermittent tingling in extremities.	Persistent numbness, tingling, and loss of sensation, especially in hands and feet.
Mobility	Subtle clumsiness or feeling unsteady.	Difficulty walking, staggering gait, or loss of balance.
Cognition	Forgetfulness, difficulty concentrating.	Significant memory loss, confusion, impaired judgment, and potential dementia.
Mental Health	Irritability, low mood.	Deep depression, anxiety, and in severe cases, paranoia or psychosis.
Gastrointestinal	Reduced appetite, mild diarrhea.	Nausea, vomiting, diarrhea, and significant weight loss.

The Risks of Long-Term, Untreated Deficiency

Leaving a B12 deficiency untreated increases risks, potentially causing:

Permanent Nerve Damage: Severe, long-standing damage may not fully recover with treatment.
Spinal Cord Degeneration: Leading to irreversible neurological problems.
Heart Problems: Including a rapid heartbeat and possible heart failure due to anemia.
Infertility: A temporary issue that usually resolves with treatment.
Increased Risk in Pregnancy: Associated with a higher risk of birth defects.
Elevated Homocysteine Levels: Linked to increased cardiovascular disease risk.

Conclusion: Seeking Diagnosis and Treatment

Recognizing the diverse symptoms of low B12 is crucial. Diagnosis typically involves blood tests. Treatment varies based on the cause and may include oral supplements or injections for absorption issues like pernicious anemia. Early treatment can reverse many symptoms, but severe neurological damage may persist. Individuals at risk, including vegans, older adults, and those with certain medical conditions, should consult a doctor.

NIH Office of Dietary Supplements fact sheet on Vitamin B12

Frequently Asked Questions

The most common initial symptoms include extreme fatigue, lack of energy, and general weakness. As the deficiency progresses, people may also experience a sore or red tongue, and a tingling or pins-and-needles sensation in their hands and feet.

Yes, low vitamin B12 can cause a range of psychological symptoms. These can include depression, irritability, anxiety, and confusion. In severe cases, more serious issues like paranoia, delusions, and memory problems can occur.

Nerve damage symptoms from a B12 deficiency can often improve with treatment, especially if the condition is caught early. However, if the deficiency is severe and has persisted for a long time, some neurological damage may become permanent.

Diagnosis is typically made through a blood test that measures the levels of vitamin B12 in your system. A doctor may also test for related issues, such as folate deficiency or underlying malabsorption problems.

For those with a dietary deficiency, increasing intake of B12-rich foods (meat, dairy, eggs) or fortified foods can be effective. However, if the deficiency is caused by an absorption issue, such as pernicious anemia, dietary changes alone will not be enough. These cases require supplements, often via injections.

A common cause is pernicious anemia, an autoimmune condition where the body attacks the stomach cells that produce intrinsic factor, a protein necessary for B12 absorption. Other causes include digestive diseases like Crohn's and celiac disease, some types of gastrointestinal surgery, and certain medications.

Yes, because B12 is found almost exclusively in animal products, those following a vegan or strict vegetarian diet are at a high risk of developing a deficiency if they do not regularly consume B12-fortified foods or take supplements.