What Happens if My B12 Level is Too Low?

October 11, 2025 •

4 min read

Vitamin B12 deficiency is a global health concern, with research showing up to 6% of the U.S. and U.K. populations affected. If your B12 level is too low, a cascade of health issues can arise, impacting everything from your energy levels and mood to your nervous system and brain function. Early identification is key to preventing potentially irreversible long-term complications.

Quick Summary

A vitamin B12 deficiency can lead to a range of symptoms, including fatigue, numbness, and balance issues, and is often misdiagnosed due to non-specific signs. Left untreated, it can cause severe neurological damage, such as peripheral neuropathy and memory loss. The condition is manageable with appropriate diagnosis and treatment, which often involves supplements or injections.

Key Points

Neurological Damage: Untreated low B12 levels can cause nerve damage, leading to symptoms like numbness, tingling, and difficulty with balance.
Anemia: A B12 deficiency can lead to megaloblastic anemia, which causes fatigue, weakness, and pale skin.
Cognitive Impairment: Severe B12 deficiency can result in memory loss, confusion, and other cognitive or psychological problems.
Causes Vary: While diet is a factor, most deficiencies are due to absorption problems, such as pernicious anemia or digestive disorders.
Treatment Options: Depending on the cause, treatment can involve oral supplements or B12 injections, with injections often needed for malabsorption issues.
Potential for Irreversible Damage: The longer a B12 deficiency goes untreated, the higher the risk of permanent nervous system damage.

The Importance of Vitamin B12 for Your Body

Vitamin B12, also known as cobalamin, is an essential nutrient that plays a crucial role in many of the body's functions. It is vital for the production of red blood cells, DNA synthesis, and the proper functioning and development of the brain and nerve cells. Your body stores excess B12 in the liver, but these reserves can become depleted if intake or absorption is consistently low over a prolonged period. When this happens, a deficiency can develop, leading to a spectrum of health issues.

Early and Common Symptoms of Low B12

When your B12 level is too low, the symptoms can be subtle at first, often mimicking other conditions. This makes accurate diagnosis challenging without a blood test. Common early signs include:

Persistent Fatigue and Weakness: One of the most common signs, resulting from the body's inability to produce enough red blood cells to transport oxygen effectively.
Megaloblastic Anemia: This is characterized by the production of abnormally large red blood cells and can be an early indicator of a B12 or folate deficiency.
Pale or Jaundiced Skin: Without a sufficient number of healthy red blood cells, your skin may take on a yellowish or pale hue.
Sore and Red Tongue (Glossitis) and Mouth Ulcers: Inflammation of the tongue is a distinctive symptom, along with the presence of mouth ulcers.
Digestive Issues: Problems such as loss of appetite, weight loss, constipation, and diarrhea are common gastrointestinal effects.

Neurological Symptoms That Can Develop

As the deficiency progresses, it can start to affect the nervous system, potentially leading to long-term or irreversible damage if not addressed promptly. Neurological symptoms include:

Peripheral Neuropathy: A 'pins and needles' sensation or numbness in the hands and feet is a classic sign of nerve damage from B12 deficiency.
Problems with Balance and Coordination (Ataxia): This can lead to difficulty walking and an increased risk of falls.
Cognitive and Psychological Problems: This can range from mild issues like memory loss and confusion to more severe conditions, including depression, anxiety, paranoia, and, in extreme cases, dementia.
Vision Disturbances: Nerve damage can affect vision, leading to visual problems.

The Serious Consequences of Ignoring Low B12

Failing to treat a vitamin B12 deficiency can have devastating consequences. The longer the condition is left untreated, the higher the risk of permanent neurological damage.

Potential Long-Term Complications:

Permanent nerve damage, which can lead to chronic numbness or paralysis.
Cognitive decline that may not fully recover even with treatment.
Infertility (which is often temporary and reversible with treatment).
Increased risk of certain autoimmune disorders in those with pernicious anemia.

Causes of Low B12 Levels

While inadequate dietary intake is a cause, especially for vegans and strict vegetarians, most deficiencies are due to malabsorption issues.

Pernicious Anemia: An autoimmune condition where the body attacks the intrinsic factor, a protein needed for B12 absorption.
Atrophic Gastritis: A thinning of the stomach lining that reduces hydrochloric acid production, needed to release B12 from food.
Gastrointestinal Surgery: Procedures like gastric bypass can limit B12 absorption.
Medications: Certain drugs, like metformin for diabetes and some heartburn medicines, can interfere with B12 absorption.
Dietary Factors: Long-term vegan or vegetarian diets without supplementation.

Comparison of Oral vs. Injectable B12 Treatments


Feature	Oral B12 Supplements	Injectable B12 (Hydroxocobalamin)
Application	Taken daily or as directed	Administered via injection (e.g., every 2-3 months)
Absorption	Can be ineffective for malabsorption	Bypasses the digestive system for guaranteed absorption
Suitability	Best for dietary-related deficiencies	Necessary for pernicious anemia and severe malabsorption
Speed of Action	Slower, depends on absorption	Faster, more immediate effect on blood levels
Dosage	High-dose oral supplements (1,000–2,000 mcg) can be as effective as injections for normalization	Standard medical treatment for severe cases

What to Do If You Suspect a B12 Deficiency

If you are experiencing any of the symptoms mentioned, it is crucial to consult a healthcare provider. A blood test can accurately diagnose the problem. A physician will then determine the best course of action based on the cause and severity of the deficiency. Treatment can range from high-dose oral supplements for dietary issues to regular injections for malabsorption problems. Some individuals may require lifelong treatment to manage their B12 levels effectively.

For more detailed information on the metabolic processes of B12, the National Center for Biotechnology Information (NCBI) offers extensive resources. The good news is that for many, addressing the deficiency can reverse symptoms and prevent further complications.

Conclusion

In summary, a low B12 level can cause a wide range of symptoms, from fatigue and mood changes to serious neurological damage if left unaddressed. Early detection is key, especially given that some of the most severe neurological issues can become permanent over time. Treatment options are highly effective, and with proper medical management, many individuals can see a significant improvement in their symptoms and overall health. If you suspect you may have a B12 deficiency, do not delay in seeking a diagnosis from your healthcare provider.

ncbi.nlm.nih.gov/books/NBK441923/

Frequently Asked Questions

The initial signs of low B12 often include fatigue, weakness, and lightheadedness. Some people also notice a painful or sore tongue and a lack of energy.

Yes, low B12 can affect your brain and nervous system, leading to cognitive problems such as memory loss, confusion, and mood changes like depression or anxiety.

A B12 deficiency is typically diagnosed through a simple blood test that measures the level of vitamin B12 in your serum. A doctor will also consider your symptoms and medical history.

Vitamin B12 is found primarily in animal products, including meat, fish, eggs, and dairy. For vegans and vegetarians, fortified foods like cereals and nutritional yeast are key sources.

If left untreated, severe B12 deficiency can cause permanent damage to the nervous system. While some symptoms improve with treatment, nerve damage, especially if long-standing, may not be fully reversible.

Individuals at higher risk for B12 deficiency include older adults, people with autoimmune conditions like pernicious anemia, those who have had gastrointestinal surgery, individuals with digestive disorders like Crohn's, and vegans or vegetarians.

The best treatment depends on the cause of the deficiency. For malabsorption issues like pernicious anemia, injections are necessary because oral supplements won't be absorbed properly. For dietary deficiencies, high-dose oral supplements may be sufficient.