Updated on: October 18, 2026
Written by: Adel Galal, Founder and Lead Writer at NextFitLife
Medical review status: This article has not been medically reviewed by a doctor, hematologist, neurologist, registered dietitian, pharmacist, or other licensed healthcare professional.
Symptoms of vitamin B12 deficiency can affect your blood, nerves, brain, balance, mouth, and energy. Some people first notice fatigue or weakness, while others develop tingling, numbness, poor balance, trouble walking, memory changes, or a sore red tongue.
The condition can be easy to miss because the symptoms are not unique to vitamin B12 deficiency. Fatigue, brain fog, mood changes, dizziness, and tingling can all have other causes.
Another important point is that vitamin B12 deficiency can affect the nervous system even when anemia is not present. A normal hemoglobin level does not always rule it out.
This article is for general information and education. It does not replace medical advice, diagnosis, or treatment.
For a broader overview of the nutrient, read Vitamin B12. For diagnosis and treatment, see Vitamin B12 Deficiency and Vitamin B12 Deficiency Treatment.
Table of Contents
- What vitamin B12 deficiency does
- 15 symptoms to know
- Fatigue
- Weakness
- Pale or yellowish skin
- Shortness of breath
- Palpitations
- Sore red tongue
- Tingling
- Numbness
- Balance problems
- Walking changes
- Brain fog
- Memory problems
- Mood changes
- Appetite or digestive changes
- Vision problems
- Symptoms without anemia
- Early symptoms
- Symptoms that are not specific
- Main causes
- Who is at higher risk
- Useful blood tests
- Borderline B12 results
- MMA and homocysteine
- When treatment may start quickly
- Recovery
- When to get medical care
- Frequently asked questions
What Does Vitamin B12 Deficiency Do to the Body?
Vitamin B12, also called cobalamin, is needed for healthy red blood cells, DNA production, and normal nerve function.
When B12 becomes too low, problems can appear in more than one body system.
Blood
Vitamin B12 deficiency can interfere with normal red blood cell development. This may lead to megaloblastic anemia, where red blood cells become unusually large and do not work normally.
Nerves
B12 deficiency can also affect peripheral nerves and the spinal cord. This can lead to neurologic symptoms such as pins and needles, numbness, poor balance, weakness, and walking problems.
Brain
Some people develop trouble concentrating, short term memory problems, confusion, depression, anxiety, or other cognitive and mental health symptoms.
15 Symptoms of Vitamin B12 Deficiency
1. Persistent Fatigue
Fatigue is a common symptom, especially when B12 deficiency causes anemia.
You may notice that ordinary tasks leave you more tired than before. Exercise may feel harder, and rest may not fully restore your usual energy.
However, fatigue is not specific to B12 deficiency. Iron deficiency, thyroid disease, sleep problems, diabetes, depression, infection, medicines, and many other conditions can cause the same symptom.
2. Weakness
Weakness may come from anemia, nerve involvement, or both.
You may find it harder to:
- Climb stairs
- Carry groceries
- Walk your normal distance
- Stand for long periods
New or rapidly worsening weakness deserves medical assessment.
3. Pale or Slightly Yellowish Skin
Anemia can make the skin look paler than usual.
In severe megaloblastic anemia, abnormal red blood cells may break down more easily, which can sometimes cause a mild yellow tone.
Yellow skin or eyes also occurs with liver disease and other blood conditions, so this symptom should not be diagnosed from appearance alone.
4. Shortness of Breath
If anemia becomes significant, less oxygen may reach tissues during activity.
You may feel breathless while:
- Climbing stairs
- Walking quickly
- Exercising
- Doing housework
Sudden or severe shortness of breath can have serious heart or lung causes and needs prompt assessment.
5. Heart Palpitations
Anemia can make the heart beat faster as the body tries to deliver enough oxygen.
You may notice:
- Pounding
- Fluttering
- A racing heartbeat
- Greater awareness of your heartbeat
Palpitations can also come from caffeine, anxiety, dehydration, thyroid disease, medications, and heart rhythm problems.
Read Heart Palpitations Causes for more detail.
6. A Sore or Red Tongue
Glossitis means inflammation of the tongue.
The tongue may become:
- Red
- Sore
- Smooth
- Tender
Mouth ulcers can also occur.
Iron deficiency, folate deficiency, infections, and other conditions may cause similar mouth symptoms.
7. Tingling in the Hands or Feet
Pins and needles can be an important nerve symptom.
People may describe:
- Prickling
- Buzzing
- Burning
- Electric sensations
This often affects the hands, feet, fingers, or toes.
Persistent tingling deserves more attention when it occurs with numbness, weakness, balance trouble, or walking changes.
8. Numbness
Long standing deficiency can reduce sensation in peripheral nerves.
Numbness may affect:
- Feet
- Toes
- Hands
- Fingers
Diabetes, nerve compression, thyroid disease, alcohol related neuropathy, and other neurologic problems can cause similar symptoms.
9. Balance Problems
B12 deficiency can affect proprioception, your ability to sense where your body is in space.
This may lead to:
- Unsteadiness
- Frequent stumbling
- Falls
- Difficulty walking in the dark
- Feeling unstable on stairs
These symptoms can suggest more significant neurologic involvement.
10. Difficulty Walking
B12 deficiency can sometimes affect the spinal cord and nerve pathways involved in movement.
You may develop:
- Weak legs
- Poor coordination
- Unsteady gait
- Reduced position sense
New walking problems need prompt medical assessment.
11. Brain Fog and Poor Concentration
Some people notice difficulty concentrating, slower thinking, or trouble following normal tasks.
This is often described as brain fog.
Brain fog is not unique to B12 deficiency. Poor sleep, menopause, iron deficiency, thyroid disease, anxiety, depression, medicines, infection, and other health problems can cause similar symptoms.
12. Memory Problems
Low B12 can be associated with short term memory problems and other cognitive changes.
You may notice difficulty:
- Remembering recent information
- Keeping track of appointments
- Following conversations
- Organizing normal tasks
Memory symptoms should be evaluated rather than automatically blamed on vitamins.
13. Mood or Mental Health Changes
Vitamin B12 deficiency can be associated with:
- Depression
- Anxiety
- Irritability
- Confusion
- Psychotic symptoms in severe cases
B12 replacement is important when deficiency is confirmed, but supplements are not a substitute for proper mental health assessment and treatment.
14. Appetite or Digestive Changes
Some people with vitamin B12 deficiency experience:
- Loss of appetite
- Weight loss
- Diarrhea
- Indigestion
These symptoms are nonspecific and can have many gastrointestinal causes.
15. Vision Problems
Severe vitamin B12 deficiency can rarely affect the optic nerve.
Possible problems include:
- Blurred vision
- Reduced visual clarity
- Missing areas in the visual field
New vision changes need prompt assessment because many eye and neurologic conditions can cause them.
Symptoms of Vitamin B12 Deficiency by Body System
| System | Possible Symptoms | What It May Suggest |
|---|---|---|
| Blood | Fatigue, weakness, paleness, shortness of breath, palpitations | Possible anemia |
| Peripheral nerves | Tingling, numbness, burning, reduced sensation | Peripheral neuropathy |
| Movement | Poor balance, falls, unsteady gait, weakness | Possible spinal cord or sensory pathway involvement |
| Brain | Brain fog, memory problems, confusion | Cognitive involvement, though many other causes are possible |
| Mouth | Red tongue, soreness, mouth ulcers | Can occur with B12 or other deficiencies |
| Eyes | Blurred vision, visual field changes | Possible optic nerve involvement |
Can Vitamin B12 Deficiency Cause Symptoms Without Anemia?
Yes.
This is one of the most important facts about vitamin B12 deficiency.
You can have:
- Normal hemoglobin
- No obvious macrocytosis
- Numbness
- Tingling
- Balance problems
- Brain fog
- Walking difficulty
A normal blood count does not completely rule out neurologic vitamin B12 deficiency.
What Are the Earliest Symptoms of Vitamin B12 Deficiency?
There is no single symptom that always appears first.
Some people notice mild fatigue or tongue soreness. Others first notice tingling, numbness, concentration problems, or subtle balance changes.
Some people have no symptoms at all.
This is why a rigid “four stages” model should not be used to diagnose vitamin B12 deficiency.
Which Symptoms Are Most Concerning?
Neurologic symptoms deserve special attention because prolonged nerve damage can become difficult to reverse.
Concerning symptoms include:
- Persistent numbness
- Worsening tingling
- Weakness
- Frequent falls
- Loss of balance
- Walking difficulty
- Vision problems
- Marked cognitive changes
Symptoms That Do Not Prove B12 Deficiency
| Symptom | Why It Is Not Specific |
|---|---|
| Fatigue | Common with poor sleep, anemia, thyroid disease, infection, diabetes, depression, and many other conditions |
| Dizziness | Can come from the inner ear, blood pressure, dehydration, anemia, medicines, or heart problems |
| Hair loss | More commonly linked with genetics, iron, thyroid disease, hormones, stress, or scalp disease |
| Low mood | Many medical and psychological conditions can contribute |
| Brain fog | Can occur with sleep problems, menopause, iron deficiency, thyroid disease, anxiety, depression, and medications |
What Causes Vitamin B12 Deficiency Symptoms?
The symptoms appear because the body does not have enough usable vitamin B12.
The reason can be low intake, poor absorption, medicine effects, surgery, or chemical inactivation.
Low dietary intake
Vitamin B12 occurs naturally mainly in animal derived foods.
People following a vegan diet need a dependable supplement or fortified food source.
Autoimmune gastritis
Autoimmune gastritis damages stomach cells involved in vitamin B12 absorption.
This can reduce intrinsic factor, which is needed for normal B12 absorption.
Stomach or bowel surgery
Risk rises after:
- Total gastrectomy
- Partial gastrectomy
- Some bariatric procedures
- Terminal ileal surgery
Crohn disease
Crohn disease involving the terminal ileum can interfere with absorption.
Celiac disease
Celiac disease can impair nutrient absorption and should sometimes be considered when the cause of B12 deficiency is not clear.
Metformin
Long term metformin use can lower vitamin B12 levels in some people.
Acid suppressing medicines
Proton pump inhibitors and H2 blockers can reduce the release of vitamin B12 from food protein.
Nitrous oxide
Nitrous oxide can chemically inactivate vitamin B12 and cause serious neurologic symptoms.
Who Is at Higher Risk?
Risk is higher in people who:
- Follow a vegan diet without reliable B12 supplementation
- Eat a very restrictive diet
- Have autoimmune gastritis
- Have had stomach surgery
- Have had bariatric surgery
- Have terminal ileal disease or surgery
- Have Crohn disease
- Have celiac disease
- Use metformin long term
- Use acid suppressing medicines long term
- Use nitrous oxide recreationally
- Are older and absorb food bound B12 less effectively
How Is Vitamin B12 Deficiency Tested?
The initial test is usually one of these:
- Total vitamin B12
- Active vitamin B12, also called holotranscobalamin
Other tests may include:
- Complete blood count
- Mean corpuscular volume
- Folate
- Methylmalonic acid
- Homocysteine
- Intrinsic factor antibody testing
- Celiac testing when the cause remains unclear
What Is a Borderline Vitamin B12 Result?
The 2024 NICE guideline provides practical adult thresholds.
| Result | Total B12 | Interpretation |
|---|---|---|
| Low | Below 180 ng/L | Deficiency is supported |
| Indeterminate | 180 to 350 ng/L | Possible deficiency and more assessment may be needed |
| Higher result | Above 350 ng/L | Deficiency is less likely |
These numbers are guides.
Your laboratory may use a validated local reference range, and symptoms, pregnancy, kidney function, supplements, and other factors still matter.
What Is Methylmalonic Acid?
Methylmalonic acid, or MMA, often rises when cells do not have enough usable vitamin B12.
MMA can be useful when:
- Total B12 is borderline
- Active B12 is indeterminate
- Symptoms strongly fit deficiency
Kidney dysfunction can also raise MMA, so the result needs careful interpretation.
What Is Homocysteine?
Homocysteine may rise with vitamin B12 deficiency.
However, it can also increase with:
- Folate deficiency
- Vitamin B6 deficiency
- Kidney dysfunction
- Other medical conditions
This makes homocysteine less specific than MMA.
Can Supplements Make B12 Testing Harder to Interpret?
Yes.
Tell your healthcare professional if you already take:
- B12 tablets
- B complex vitamins
- Multivitamins
- Sublingual B12
- B12 injections
Supplements can increase measured blood B12 even when the cause of symptoms has not been fully established.
Can Treatment Start Before Every Test Result Returns?
Yes, in selected situations.
When serious neurologic or hematologic problems could worsen quickly, clinicians may start vitamin B12 replacement while additional testing is still underway.
This may be appropriate when there is:
- Ataxia
- Major walking difficulty
- Significant anemia
- A suspected irreversible absorption problem
- Relevant gastrointestinal surgery
- Pregnancy or breastfeeding with an indeterminate test result
How Are Symptoms of Vitamin B12 Deficiency Treated?
Treatment usually involves:
- Oral vitamin B12
- Intramuscular vitamin B12
- Correcting dietary deficiency
- Treating or managing the underlying cause
Oral treatment works well for many people.
Injections may be preferred when there is severe malabsorption, important neurologic disease, autoimmune gastritis, total gastrectomy, or complete terminal ileum removal.
Read Vitamin B12 Deficiency Treatment for a full treatment plan.
How Quickly Do Symptoms Improve?
Recovery is different for each person.
NICE advises that symptoms may begin improving within about two weeks, although meaningful improvement can take up to three months.
Some symptoms take much longer.
Nerve symptoms usually recover more slowly than blood abnormalities.
Read How Long to Recover From Vitamin B12 Deficiency.
Can Nerve Damage Become Permanent?
Yes.
Many neurologic symptoms improve after treatment, especially when deficiency is recognized early.
Long standing severe nerve damage may recover only partly.
This is why worsening numbness, balance trouble, weakness, or walking difficulty should not be ignored.
What If Symptoms Continue After Treatment?
Persistent symptoms do not always mean you need a larger dose of B12.
Possible explanations include:
- The nerves need more time to recover
- The oral dose is inadequate
- Absorption is poor
- The treatment is not being taken consistently
- The cause of deficiency continues
- Another nutrient deficiency is present
- Another medical condition is causing the symptoms
A follow up visit should review both the diagnosis and the treatment plan.
When Should Follow Up Happen?
Current NICE guidance recommends an initial follow up around three months after treatment begins, or sooner when symptoms are severe.
Pregnancy or breastfeeding may need earlier follow up.
The review should ask:
- Are symptoms improving?
- Are they getting worse?
- Have new symptoms developed?
- Is treatment being taken correctly?
A Practical Action Plan
- Do not diagnose deficiency from fatigue alone.
- Pay special attention to numbness, tingling, balance trouble, and walking changes.
- Do not rule out deficiency just because anemia is absent.
- Review diet and fortified food intake.
- Review metformin and acid suppressing medicine use.
- Tell your healthcare professional about gastrointestinal surgery or bowel disease.
- Mention nitrous oxide use if relevant.
- Use total or active B12 testing when appropriate.
- Use MMA when the first result is indeterminate.
- Find the cause rather than treating only the laboratory number.
- Start appropriate replacement when deficiency is confirmed or strongly suspected.
- Do not delay treatment when serious neurologic disease is present.
- Attend follow up if symptoms persist or return.
- Continue lifelong replacement when the cause is irreversible.
When Should You See a Doctor?
Arrange medical assessment if you have:
- Persistent unexplained fatigue
- New tingling or numbness
- Balance problems
- Unsteady walking
- Memory or concentration changes
- A sore red tongue
- Unexplained anemia
- A vegan diet without a reliable B12 source
- Previous stomach or intestinal surgery
- Crohn disease or celiac disease
- Long term metformin use with relevant symptoms
- Long term acid suppressing medicine use with relevant symptoms
- Repeated recreational nitrous oxide use
When Are Symptoms More Urgent?
Seek prompt medical care for:
- Rapidly worsening numbness
- New major walking difficulty
- Severe weakness
- Major balance loss
- Marked confusion
- Significant vision changes
- Chest pain
- Fainting
- Severe shortness of breath
These symptoms may have causes other than B12 deficiency and should not be treated with supplements alone.
Conclusion: Take Symptoms of Vitamin B12 Deficiency Seriously
Symptoms of vitamin B12 deficiency can range from fatigue and tongue soreness to numbness, balance problems, walking changes, memory trouble, and vision problems.
The key point is that neurologic symptoms can occur even when anemia is absent. A normal blood count does not always close the case.
If symptoms and risk factors fit, ask whether total B12, active B12, or methylmalonic acid testing is appropriate. If neurologic symptoms are worsening, seek medical care early rather than waiting for supplements or diet changes to work.
Early diagnosis gives blood and nerves the best chance to recover.
References and Sources
- NICE. Vitamin B12 Deficiency in Over 16s: Diagnosis and Management.
Covers symptoms, risk factors, total and active B12 testing, MMA, nitrous oxide, treatment, and follow up.
https://www.nice.org.uk/guidance/ng239 - National Institutes of Health Office of Dietary Supplements. Vitamin B12 Fact Sheet for Health Professionals.
Covers vitamin B12 function, anemia, neurologic symptoms, glossitis, MMA, food sources, metformin, acid suppressants, and malabsorption.
https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/ - National Institutes of Health Office of Dietary Supplements. Vitamin B12 Fact Sheet for Consumers.
Covers fatigue, weakness, numbness, tingling, balance problems, memory changes, depression, confusion, and food sources.
https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/ - NHS. Vitamin B12 or Folate Deficiency Anaemia: Symptoms.
Covers tiredness, weakness, palpitations, shortness of breath, sore tongue, cognitive symptoms, numbness, balance problems, pins and needles, and vision changes.
https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/symptoms/ - NHS. Vitamin B12 or Folate Deficiency Anaemia.
Covers causes, anemia, nervous system effects, dietary deficiency, pernicious anemia, and the need for timely treatment.
https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/ - MedlinePlus. Vitamin B12 Level.
Covers B12 testing, intrinsic factor, nerve symptoms, medicines, and causes of abnormal B12 levels.
https://medlineplus.gov/ency/article/003705.htm
Internal Links and Helpful NextFitLife Guides
- Vitamin B12: 13 Critical Facts for Better Health
- Vitamin B12 Deficiency: Symptoms, Causes, Tests and Treatment
- Signs of B12 Deficiency: 14 Critical Warning Clues
- Vitamin B12 Deficiency Treatment: 11 Proven Steps
- Vitamin B12 Deficiencies
- How Long to Recover From Vitamin B12 Deficiency
- How Long After Starting Vitamin B12 Will I Feel Better?
- Vitamin D Deficiency
- Low Calcium Signs and Symptoms
- Heart Palpitations Causes
- NextFitLife Health Hub
About the Author
Adel Galal is a father of four, three sons and a daughter, and a grandfather of four, with 33 years of hands on parenting experience. He is the founder of Parnthub.com, based in Cairo, Egypt, where he shares practical guidance on feeding, development, and family life from newborns to teenagers.
Adel is not a medical professional. Health articles cite trusted medical and public health sources and are written for general information and education.
I am not a doctor or licensed healthcare professional, and this content does not replace professional medical advice, diagnosis, or treatment. I share information based on extensive research, real life experience, and consultation with healthcare providers. Always consult a qualified healthcare professional for diagnosis, treatment, or guidance about any health condition.
Learn more on the NextFitLife About Us page.
Frequently Asked Questions
What are the main symptoms of vitamin B12 deficiency?
Main symptoms can include fatigue, weakness, pale skin, shortness of breath, palpitations, a sore red tongue, tingling, numbness, balance problems, walking difficulty, brain fog, memory changes, mood changes, appetite changes, and sometimes vision problems.
What are early symptoms of vitamin B12 deficiency?
There is no fixed first symptom. Some people notice fatigue, weakness, tongue soreness, tingling, numbness, poor concentration, or subtle balance trouble. Others have no early symptoms.
Can you have vitamin B12 deficiency without anemia?
Yes. Neurologic symptoms such as tingling, numbness, balance problems, gait changes, and cognitive symptoms can occur without anemia or macrocytosis.
Can vitamin B12 deficiency cause tingling?
Yes. Pins and needles in the hands or feet are common neurologic symptoms of vitamin B12 deficiency.
Can vitamin B12 deficiency cause numbness?
Yes. Long standing deficiency can affect peripheral nerves and reduce sensation in the hands, fingers, feet, or toes.
Can B12 deficiency affect balance?
Yes. It can impair position sense and coordination, leading to unsteadiness, falls, or difficulty walking.
Can B12 deficiency cause brain fog?
Yes. Difficulty concentrating and short term memory problems can occur, but many other health and lifestyle problems can cause similar symptoms.
Can B12 deficiency cause memory problems?
Yes. Vitamin B12 deficiency can be associated with short term memory problems, confusion, and other cognitive changes.
Can B12 deficiency affect mood?
Yes. It may be associated with depression, anxiety, irritability, confusion, and other mental health symptoms, but these symptoms still require proper assessment.
Can vitamin B12 deficiency cause vision problems?
Severe deficiency can sometimes affect the optic nerve and cause blurred vision or visual field changes. New vision symptoms need prompt assessment.
Does normal hemoglobin rule out vitamin B12 deficiency?
No. Vitamin B12 deficiency can affect the nervous system even when hemoglobin is normal and macrocytosis is absent.
What causes vitamin B12 deficiency?
Causes include low intake, autoimmune gastritis, gastrointestinal surgery, Crohn disease, celiac disease, metformin, acid suppressing medicines, and nitrous oxide.
Can metformin cause vitamin B12 deficiency?
Yes. Long term metformin can lower vitamin B12 levels in some people. Do not stop it without medical advice.
Can acid reflux medicines lower B12?
Long term use of proton pump inhibitors or H2 blockers can reduce the release of vitamin B12 from food and contribute to deficiency in some people.
Can nitrous oxide cause B12 deficiency?
Yes. Nitrous oxide can inactivate vitamin B12 and cause serious neurologic symptoms, sometimes even when serum B12 does not appear very low.
What test checks vitamin B12 deficiency?
Total B12 or active B12 is usually used first. MMA can help when an initial result is indeterminate.
What is a borderline vitamin B12 level?
NICE considers total B12 from 180 to 350 ng/L an indeterminate adult range. Symptoms, risk factors, laboratory ranges, and further testing help guide interpretation.
What is methylmalonic acid?
Methylmalonic acid, or MMA, is a functional marker that often rises when cells lack usable vitamin B12. Kidney dysfunction can also raise MMA.
How quickly do B12 symptoms improve after treatment?
Symptoms may begin improving within about two weeks, but improvement can take up to three months and complete recovery may take much longer. Nerve symptoms often improve slowly.
When are symptoms of vitamin B12 deficiency urgent?
Seek prompt care for rapidly worsening numbness, new major walking difficulty, severe weakness, major balance loss, marked confusion, significant vision change, chest pain, fainting, or severe shortness of breath.
Health & wellness writer with 30+ years of experience in nutrition, fitness, and healthy aging. Founder of NextFitLife.com — evidence-based health guidance.
