How do I tell if my vitamin B12 is low? Early signs and symptoms

January 8, 2026 •

2 min read

According to the National Institutes of Health, up to 43% of older adults may have low vitamin B12 levels. Knowing how to tell if your vitamin B12 is low is crucial, as this deficiency can manifest through a wide range of physical, neurological, and psychological symptoms that often start subtly and worsen over time.

Quick Summary

An undetected vitamin B12 deficiency can cause symptoms ranging from fatigue and pale skin to neurological issues like numbness and difficulty walking. Early recognition is key to preventing long-term complications. Blood tests are essential to confirm a deficiency and differentiate it from other conditions, with specific lab markers indicating low levels.

Key Points

Subtle Onset: Vitamin B12 deficiency symptoms, such as fatigue and weakness, can develop slowly over time and be easily dismissed.
Neurological Impact: Symptoms like tingling, numbness, and balance issues are key signs of a B12 problem, and can occur even without anemia.
Diagnostic Bloodwork: A diagnosis is confirmed through blood tests, including a CBC, serum B12 levels, and the more specific MMA and homocysteine tests.
High-Risk Groups: Vegans, older adults, and those with certain gastrointestinal issues or surgeries are at a higher risk and should be particularly vigilant.
Preventative Action: Early detection and treatment with oral supplements or injections can prevent long-term neurological complications from untreated deficiency.
Differentiating Deficiencies: Unlike folate deficiency, a B12 deficiency is characterized by elevated methylmalonic acid (MMA) and often includes neurological symptoms.

Recognizing the Early Warning Signs of Low Vitamin B12

Vitamin B12 is essential for nerve function, DNA synthesis, and red blood cell production. Since the body stores a large reserve of B12 in the liver, symptoms of a deficiency can take years to appear after dietary changes, making early detection difficult without proactive testing. The initial signs are often non-specific and can be mistaken for other conditions.

General and Physical Symptoms

Fatigue is one of the most common early indicators due to impaired red blood cell production, causing a persistent and unusual tiredness. Other physical signs may include pale or jaundiced skin, a sore and red tongue (glossitis), mouth ulcers, gastrointestinal issues, and unintended weight loss.

Neurological and Psychological Symptoms

B12's critical role in nerve health means a deficiency can significantly affect the nervous system. Neurological symptoms, such as numbness and tingling (paresthesia) in the hands and feet, difficulty with balance and coordination (ataxia), memory loss, confusion, depression, and irritability, can appear even before anemia and may become permanent if not treated.

The Diagnostic Process for Low Vitamin B12

Suspected B12 deficiency requires confirmation through medical testing. While a standard serum B12 test is common, borderline results may necessitate further investigation.

Key Blood Tests for Confirmation

Several blood tests are used to confirm a B12 deficiency:

Complete Blood Count (CBC): Can detect macrocytic anemia, a common sign.
Serum Vitamin B12 Levels: Measures blood B12. Levels below 200 pg/mL suggest deficiency, while 200-300 pg/mL are borderline.
Methylmalonic Acid (MMA) Test: A more sensitive indicator; elevated levels strongly suggest deficiency and are not affected by folate.
Homocysteine Test: Measures homocysteine; elevated levels can indicate either B12 or folate deficiency.

Comparison of Deficiency Indicators


Indicator	Vitamin B12 Deficiency	Folate Deficiency
Megaloblastic Anemia	Yes (often with hypersegmented neutrophils)	Yes
Neurological Symptoms	Yes (paresthesia, nerve damage)	No (usually absent)
Elevated MMA Levels	Yes	No
Elevated Homocysteine	Yes	Yes
Sore Tongue (Glossitis)	Yes	Yes (sometimes)

Who Is at Risk for Low Vitamin B12?

Certain individuals are more susceptible to B12 deficiency:

Vegans and Vegetarians: B12 is primarily in animal products, requiring supplementation or fortified foods for those on plant-based diets.
Older Adults: Reduced stomach acid impairs B12 absorption from food with age.
Individuals with Gastrointestinal Disorders: Conditions like Crohn's, celiac disease, and pernicious anemia hinder B12 absorption.
People with Gastric Surgery: Procedures altering the stomach or intestine can affect absorption.
Those on Certain Medications: Some medications, such as metformin and proton pump inhibitors, can lower B12 over time.

Conclusion

Identifying the subtle signs of a B12 deficiency is vital for timely diagnosis and treatment. Symptoms can be varied, but proactive blood testing is key. If you experience persistent fatigue, neurological symptoms like tingling or numbness, or mood changes, consult a healthcare professional. Early detection and treatment can help prevent long-term complications.

Disclaimer: The information provided is for educational purposes only and should not be considered medical advice. Always consult with a healthcare professional for diagnosis and treatment.

Frequently Asked Questions

For immediate treatment of significant deficiency, injections of vitamin B12 are often the fastest method as they bypass absorption issues. For less severe cases, high-dose oral supplements can also be very effective.

Early signs can be subtle and include persistent fatigue, general weakness, a sore and red tongue (glossitis), and potentially a yellowish or pale skin tone.

Yes, psychological symptoms such as depression, irritability, and anxiety are associated with vitamin B12 deficiency, possibly due to its impact on neurotransmitter production.

Yes, tingling or a pins-and-needles sensation, known as paresthesia, is a very common neurological symptom of a vitamin B12 deficiency.

Recovery time varies based on the severity of the deficiency and the treatment method. While anemia can resolve in about six weeks, neurological symptoms, especially if long-standing, can take months or even years to improve and may not fully reverse.

Yes, some individuals may have a low-normal serum B12 level but still have a deficiency. In these cases, doctors may need to order more sensitive tests, such as a methylmalonic acid (MMA) test, to confirm the diagnosis.

Vitamin B12 is found primarily in animal products like meat, fish, eggs, and dairy. Good sources include beef, clams, salmon, fortified cereals, and nutritional yeast.