Understanding What Can Untreated B12 Deficiency Lead to

October 11, 2025 •

3 min read

According to the National Institutes of Health, vitamin B12 deficiency can cause serious complications, including permanent nerve damage if left unaddressed. Understanding what can untreated B12 deficiency lead to is crucial for early detection and preventing long-term, devastating health consequences.

Quick Summary

A persistent lack of vitamin B12 can cause irreversible neurological damage, severe megaloblastic anemia, and psychological issues like depression. It can also increase the risk of cardiovascular disease due to elevated homocysteine and lead to fertility and pregnancy complications.

Key Points

Irreversible Neurological Damage: Prolonged B12 deficiency can destroy the myelin sheath around nerves, leading to permanent issues like tingling (paresthesia), numbness, memory loss, and difficulty walking (ataxia).
Severe Anemia: It causes megaloblastic anemia, where large, immature red blood cells can't function properly, resulting in fatigue, weakness, and paleness. In severe cases, this can lead to heart failure.
Psychiatric Disorders: The deficiency can cause or worsen mental health problems, including depression, paranoia, hallucinations, and cognitive decline that can mimic dementia.
Cardiovascular Risk: Elevated levels of homocysteine, caused by a lack of B12, are associated with an increased risk of heart attacks and strokes.
Birth Defects: Deficiency in pregnant women can cause severe neural tube defects in their babies, such as spina bifida.
Risk of Misdiagnosis: B12 deficiency symptoms can be mistaken for other illnesses, especially neurological or psychiatric conditions, delaying appropriate and simple treatment.
Gradual Onset: Symptoms often develop slowly over many years due to the body's ability to store B12, which can delay diagnosis and lead to more serious complications.

Vitamin B12, or cobalamin, is an essential water-soluble vitamin vital for numerous bodily functions, including nerve cell health, red blood cell formation, and DNA synthesis. While the body can store a significant amount of B12, a chronic deficit can deplete these reserves over several years, leading to a wide range of severe health complications if left undiagnosed and untreated. The effects can be gradual, sometimes starting years before a person experiences severe symptoms, making early recognition and intervention critical.

Neurological and Psychiatric Damage

Perhaps the most feared consequence of untreated B12 deficiency is the potential for irreversible neurological damage. The vitamin is essential for maintaining the myelin sheath, the protective layer around nerve fibers. Without adequate B12, this sheath can break down, impairing nerve signaling and leading to lasting damage.

Spectrum of Neurological Symptoms

Paresthesia: A tingling, numbness, or "pins and needles" sensation, often starting in the hands and feet.
Ataxia: A loss of physical coordination that can affect walking, speaking, and balance.
Subacute combined degeneration (SCD): A progressive, degenerative condition affecting the spinal cord's dorsal and lateral columns, characterized by severe sensory and motor issues.
Optic neuropathy: Damage to the optic nerve, which can lead to vision problems or even blindness.

Psychological and Cognitive Complications

B12 deficiency can severely impact mental health, with symptoms that may appear even before anemia develops. This can lead to misdiagnosis, as the symptoms overlap with various psychiatric conditions.

Mood Changes: Including depression, irritability, and anxiety.
Cognitive Impairment: Affecting memory, concentration, and judgment, which can progress to dementia.
Psychosis: In severe cases, paranoia, hallucinations, and delusions may occur.

Hematological and Cardiovascular Problems

B12 deficiency disrupts DNA synthesis, particularly affecting the rapidly dividing cells in bone marrow. This leads to the characteristic hematological issues associated with the condition.

Megaloblastic Anemia

Untreated deficiency often results in megaloblastic anemia, a condition where red blood cells are abnormally large and immature. This reduces the blood's oxygen-carrying capacity, causing symptoms like:

Extreme fatigue and weakness
Pale skin
Shortness of breath and rapid heartbeat
Dizziness In very severe cases, pancytopenia, a reduction in all blood cell lines, can occur.

Cardiovascular Risks

B12 is a cofactor in the conversion of homocysteine to methionine. A deficiency causes homocysteine levels to build up, a condition known as hyperhomocysteinemia. Elevated homocysteine is a known risk factor for cardiovascular diseases, including heart attack and stroke.

Maternal and Fetal Consequences

For pregnant individuals, B12 deficiency poses a serious risk to the unborn baby. It is crucial for the development of the brain and spinal cord.

Neural Tube Defects: Inadequate B12 during pregnancy can increase the risk of serious birth defects like spina bifida and anencephaly.
Developmental Delays: Infants born to B12-deficient mothers may experience developmental delays.
Temporary Infertility: In adults, a deficiency can sometimes lead to temporary infertility, which often resolves with treatment.

Symptom Comparison: Early vs. Advanced Deficiency


Symptom Category	Early Deficiency	Advanced, Untreated Deficiency
Neurological	Tingling or numbness in hands/feet, mild cognitive issues, fatigue.	Severe nerve damage, subacute combined degeneration (spinal cord), peripheral neuropathy, vision loss, ataxia.
Psychological	Irritability, depression, mild memory issues.	Severe depression, paranoia, delusions, hallucinations, dementia.
Hematological	Mild anemia, potentially masked by normal folate levels.	Megaloblastic anemia, pancytopenia, heart failure.
Other Physical	Sore, red tongue (glossitis), mouth ulcers, fatigue.	Incontinence, severe gastrointestinal issues, increased cardiovascular risk.

Conclusion: The Importance of Early Intervention

Ignoring a vitamin B12 deficiency can lead to a progressive and debilitating cascade of health issues affecting the nervous, hematological, and psychological systems. Many symptoms, particularly those affecting the brain and nerves, may become permanent if not treated promptly. The good news is that for most cases, especially if caught early, B12 deficiency is easily treatable with supplements or injections. Anyone experiencing symptoms or belonging to a high-risk group—such as older adults, vegans, those with certain gastrointestinal conditions, or those on particular medications—should consult a healthcare provider for testing and appropriate management. Proactive care can prevent these severe, life-altering consequences and restore health.

For more information on B12 deficiency and its complications, visit the National Heart, Lung, and Blood Institute.

Frequently Asked Questions

The most serious consequence is irreversible neurological damage, including subacute combined degeneration of the spinal cord and peripheral neuropathy, which can cause permanent numbness, tingling, and motor function problems.

Yes, B12 deficiency is known to cause a range of psychological and psychiatric issues, such as depression, irritability, anxiety, memory loss, and even psychosis in advanced cases.

No, a person can experience severe neurological and psychiatric symptoms without showing signs of anemia. The neurological damage can occur independently of, or even before, hematological issues appear.

A lack of B12 causes high levels of homocysteine to accumulate in the blood. Elevated homocysteine is a risk factor for cardiovascular diseases, including stroke and heart attack.

The body stores a significant amount of B12 in the liver, so a deficiency can take several years to develop, allowing symptoms to worsen gradually over time. The onset of severe, potentially irreversible problems depends on the duration and severity of the deficiency.

Yes, if B12 deficiency and its related nerve damage are left untreated for too long, the damage may become permanent. Early diagnosis and prompt treatment offer the best chance of a full or significant recovery.

During pregnancy, insufficient B12 can increase the risk of serious birth defects, such as neural tube defects (e.g., spina bifida). It can also cause developmental delays in infants.