What does lack of B12 do to your body?

November 16, 2025 •

3 min read

According to the National Institutes of Health, up to 20% of older adults may not absorb vitamin B12 well, leading to a deficiency. Understanding what does lack of B12 do to your body is crucial for recognizing early signs and preventing long-term damage.

Quick Summary

Vitamin B12 deficiency impacts the nervous system and red blood cell production, causing symptoms from fatigue and nerve damage to psychological issues like depression and memory loss. The effects can be gradual and worsen over time if untreated.

Key Points

Neurological Damage: Severe and prolonged B12 deficiency can cause irreversible nerve damage, affecting sensation, coordination, and mental function.
Megaloblastic Anemia: A lack of B12 impairs DNA synthesis, leading to abnormally large, dysfunctional red blood cells, causing fatigue, weakness, and pale skin.
Psychological Effects: Low B12 can significantly impact mental health, contributing to depression, anxiety, confusion, and memory loss.
Diverse Causes: Deficiency can result from dietary choices (veganism), malabsorption issues (like pernicious anemia), or the use of certain medications.
Treatment is Crucial: Depending on the cause, B12 deficiency is treated with oral supplements or injections, which can reverse symptoms, but early intervention is key for neurological issues.
Risk in Older Adults: Older individuals are particularly susceptible to B12 deficiency, often due to decreased stomach acid and reduced absorption.
Masking by Folate: High folate intake can conceal the anemia aspect of B12 deficiency, allowing neurological damage to worsen undetected.

Vitamin B12, or cobalamin, is a crucial nutrient for nerve health, red blood cell formation, and DNA synthesis. A deficiency can result in a wide range of symptoms that often develop slowly and may be mistaken for other conditions. Recognizing the effects of low B12 is important for early diagnosis and treatment to prevent irreversible damage.

The Physical Toll of Low B12

A common outcome of insufficient B12 is megaloblastic anemia, where the body produces large, immature red blood cells that don't function properly. This reduces oxygen transport, leading to symptoms such as fatigue, weakness, pale skin, a sore tongue, and gastrointestinal issues. A rapid heartbeat and breathlessness can also occur as the heart compensates for reduced oxygen.

Neurological and Psychological Impacts

B12 is vital for maintaining the myelin sheath around nerve fibers. Deficiency can degrade this sheath, causing nerve damage, particularly in the spinal cord, which can become permanent if untreated. Symptoms include peripheral neuropathy (pins and needles), cognitive decline (memory issues, confusion), ataxia (loss of coordination), vision problems, and mood changes (irritability, depression, anxiety). In older adults, cognitive issues can resemble dementia.

Common Causes of B12 Deficiency

Since the body doesn't produce B12, it must come from animal products or supplements. Causes of deficiency are generally dietary insufficiency, malabsorption, or other factors.

Dietary Insufficiency: Vegans and vegetarians who don't supplement are at high risk.
Malabsorption: The most frequent cause. Conditions include:
- Pernicious Anemia: An autoimmune disease hindering B12 absorption.
- Gastritis: Stomach inflammation reducing acid needed for B12 release from food; common in older adults.
- Digestive Diseases: Conditions like Crohn's or celiac disease affecting absorption in the small intestine.
- Bariatric Surgery: Procedures altering the stomach or small intestine impacting absorption.
Medications and Other Factors: Certain drugs (like metformin and proton pump inhibitors) and chronic alcohol use can interfere with B12 absorption.

Diagnosis and Treatment Options

Diagnosis typically involves blood tests to check for macrocytosis and measure B12, methylmalonic acid (MMA), and homocysteine levels. Treatment varies by cause. Diet-related deficiencies may be managed with oral supplements. Malabsorption often requires B12 injections, which may be needed long-term.

Comparing Vitamin B12 and Folate Deficiency

Both B12 and folate (B9) are essential B vitamins involved in metabolism and DNA synthesis, and a deficiency in either can cause megaloblastic anemia. However, their impact on the nervous system differs significantly.


Feature	Vitamin B12 Deficiency	Folate (B9) Deficiency
Associated Anemia	Megaloblastic Anemia	Megaloblastic Anemia
Neurological Symptoms	Common, potential for irreversible damage	Rare
Unique Complications	Spinal cord damage, paranoia, psychosis	Neural tube defects in infants (if pregnant)
Masking Effect	High folate can hide anemia, allowing neurological damage to progress	Not applicable
Primary Sources	Animal products, fortified foods	Leafy greens, citrus, legumes, fortified grains

Conclusion

A lack of B12 profoundly affects the body, impacting energy, digestion, nerve function, and mental health. Symptoms can be subtle initially but worsen over time, potentially causing irreversible neurological damage. Early diagnosis through blood tests and prompt treatment with supplements or injections are crucial for managing the condition and preventing serious long-term complications. Consult a healthcare provider if you suspect a deficiency for accurate diagnosis and treatment. Learn more about B12 deficiency on the {Link: Cleveland Clinic website https://my.clevelandclinic.org/health/diseases/22831-vitamin-b12-deficiency}.

Long-Term Health Risks

Chronic or severe B12 deficiency can lead to serious long-term health issues:

Spinal Cord Degeneration: Progressive loss of coordination and sensation in severe cases.
Cardiovascular Issues: Strain on the heart from severe anemia can lead to complications.
Infertility: Temporary infertility has been linked and often resolves with treatment.
Increased Risk of Cancer: Pernicious anemia is associated with a higher risk of stomach cancer.
Birth Defects: Deficiency during pregnancy can increase the risk of neural tube defects.

What to Do If You Have Symptoms

If you experience symptoms of B12 deficiency, consult a healthcare provider. They can order blood tests to confirm the diagnosis and identify the cause, which is key to effective treatment. Managing B12 levels is manageable once identified, but ignoring symptoms can have lasting consequences.

Frequently Asked Questions

Early symptoms often include fatigue, general weakness, and a persistent lack of energy. A pale or yellow-tinged skin, shortness of breath, and a sore tongue are also common first indicators.

B12 deficiency affects the brain by impacting nerve function and neurotransmitter synthesis, leading to cognitive issues like memory loss, confusion, and difficulty concentrating. It can also cause mood changes, including depression and irritability.

Yes, B12 deficiency is treatable, and symptoms can improve or be reversed with appropriate supplementation. However, if severe neurological damage has occurred, particularly in long-term cases, it may be permanent.

People over 60, strict vegans or vegetarians, individuals with certain digestive diseases like Crohn's or Celiac, those with pernicious anemia, and patients who have undergone bariatric surgery are at higher risk.

Pernicious anemia is an autoimmune disease and one of the most common causes of B12 deficiency. It prevents the absorption of B12, but other factors like diet or surgery can also cause B12 deficiency without it being pernicious anemia.

For most people with a dietary deficiency, high-dose oral supplements are effective. However, for malabsorption issues like pernicious anemia, injections are generally necessary because the body cannot absorb the oral form effectively.

Yes, because of its wide range of symptoms, B12 deficiency is often misdiagnosed. Early signs like fatigue and cognitive issues can be confused with stress, aging, or other neurological and psychological disorders.