B12 Deficiency: Symptoms, Causes, Tests, Treatment

Introduction

Vitamin B12 deficiency can affect the blood, nerves, thinking, and mood ^[3,4,8]. Symptoms may develop slowly and differ from one person to another ^[2,7].

The body stores large amounts of vitamin B12 in the liver ^[2,3]. Therefore, symptoms may take several years to appear ^[2].

Early diagnosis is important. Some nerve problems may become permanent when treatment is delayed ^[6].

This guide explains vitamin B12 deficiency symptoms, causes, testing and treatment. It also covers risk factors, warning signs, and follow-up care.

Overview of Vitamin B12 Deficiency

Vitamin B12 deficiency is also called cobalamin deficiency. It occurs when the body does not get or absorb enough B12 ^[3,8].

Low B12 can harm blood cell production and normal nerve function ^[3,4]. It can also cause physical, mental, and mood-related symptoms ^[8].

Some people develop vitamin B12 deficiency anemia. Anemia means there are too few healthy red blood cells ^[1].

Red blood cells carry oxygen to tissues throughout the body ^[1]. Too few healthy cells can cause tiredness and other symptoms ^[1,2].

However, anemia is not always present. Vitamin B12 deficiency can cause nerve or thinking problems without megaloblastic anemia ^[5,6].

Why the body needs vitamin B12

Vitamin B12 is required for DNA synthesis and healthy blood cell production ^[3,4]. It also supports normal myelin and nerve function ^[3].

DNA contains the instructions that guide the body’s cells. Myelin is the protective layer around many nerves.

Vitamin B12 helps the body produce healthy red blood cells ^[1,4]. It also supports the production of white blood cells and platelets ^[4].

Red blood cells carry oxygen to body tissues ^[1]. White blood cells support the immune system. Platelets help the blood clot.

Vitamin B12 comes from food or supplements because the body cannot make it ^[4]. Natural food sources are mainly animal foods ^[3,9].

How deficiency affects blood cells and nerves

Without enough vitamin B12, blood cells may not develop correctly ^[4]. This can cause megaloblastic anemia ^[2].

In megaloblastic anemia, red blood cells become unusually large and do not work normally ^[2]. This can reduce healthy oxygen-carrying cells.

Possible effects include fatigue, weakness, shortness of breath, and heart palpitations ^[1,2]. Palpitations feel like pounding, racing, or skipped heartbeats.

Low B12 can also harm the nervous system ^[3,8]. It may affect feeling, balance, walking, memory, concentration, or mood ^[5,8].

These nerve effects can occur without signs of anemia ^[5,6]. A normal blood count does not always rule out a B12-related nerve problem ^[5,6].

Why symptoms may take years to appear

The body stores far more vitamin B12 than it uses each day ^[2,3]. Most of these stores are held in the liver ^[3].

These stores may delay symptoms for several years ^[2]. Deficiency can still develop when intake or absorption remains too low ^[3].

This slow process may make the condition hard to notice. A person may adjust to fatigue or reduced activity over time.

Many possible symptoms can also have other causes. Medical testing is needed to find out whether low B12 is involved ^[5,6].

Vitamin B12 Deficiency Symptoms and Warning Signs

Vitamin B12 deficiency symptoms vary in type and severity ^[7,10]. Some people mainly have symptoms linked to anemia ^[6,8].

Others develop nerve, balance, thinking, or mood changes ^[5,8]. Symptoms may be mild at first and worsen over time ^[2,6].

Understanding vitamin B12 deficiency symptoms, causes, testing and treatment may support earlier care. This matters because delayed treatment may limit nerve recovery ^[6].

Common anemia-related symptoms

Possible symptoms include:

• Fatigue or unusual tiredness ^[2,10]
• General weakness ^[2]
• Pale skin ^[2]
• Shortness of breath ^[1]
• Heart palpitations ^[2]
• Loss of appetite ^[2]
• Unplanned weight loss ^[2]
• A sore or inflamed tongue ^[2,5]

These symptoms may appear slowly because the body has large B12 stores ^[2]. People may reduce daily activity without knowing why.

Fatigue by itself does not prove B12 deficiency. A clinician must consider symptoms, risks, examination findings, and test results ^[5,6].

Other health problems can cause similar symptoms. Testing helps separate B12 deficiency from other possible causes ^[5,6].

Nerve, balance, and cognitive symptoms

Vitamin B12 deficiency can affect nerves outside the brain and spinal cord ^[3,8]. These are known as peripheral nerves.

Damage to these nerves is called peripheral neuropathy. It may cause numbness, tingling, burning, or reduced feeling ^[5,10].

Possible nerve and balance symptoms include:

• Numbness in the hands or feet ^[5,10]
• Tingling or pins and needles ^[5,10]
• Trouble walking ^[5,10]
• Problems with balance ^[5,10]
• Poor coordination, also called ataxia ^[10]
• Peripheral neuropathy ^[10]

Vitamin B12 deficiency may also affect thought and mood ^[5,8]. Possible symptoms include:

• Memory loss or short-term memory problems ^[5]
• Trouble thinking clearly ^[5,10]
• Confusion ^[5]
• “Brain fog” ^[10]
• Depression ^[8,10]
• Other mental health symptoms ^[8]

Neurological symptoms can occur without megaloblastic anemia ^[5,6]. Neurological means related to the brain, spinal cord, or nerves.

Therefore, the absence of anemia should not end every B12 evaluation ^[5,6]. Symptoms and risk factors still need careful review ^[6].

Delayed diagnosis can lead to lasting nerve problems ^[6]. Nerve recovery may also be incomplete when treatment starts late ^[6].

When to See a Doctor

Arrange a medical visit if you have possible symptoms and risk factors. Testing is reasonable when at least one symptom and one risk factor occur together ^[7,10].

Common risk factors include low dietary intake and older age ^[3,10]. They also include poor absorption, certain medicines, and digestive surgery ^[5,10].

Seek prompt medical care for:

• New or worsening weakness
• Trouble standing or walking
• Fast-worsening numbness
• Loss of sensation
• New confusion
• Severe shortness of breath
• Chest pain
• Severe palpitations

Severe shortness of breath and palpitations can occur with anemia ^[1,2]. New nerve symptoms also need timely assessment because some damage may become permanent ^[6].

Chest pain, severe breathing trouble, or sudden confusion may need emergency care. Do not wait for a routine visit when symptoms are severe.

Medical testing is safer than self-diagnosis. The correct treatment depends on the cause and the person’s ability to absorb B12 ^[5,6].

Causes and Risk Factors

Vitamin B12 deficiency usually comes from low intake, poor absorption, or both ^[3,8]. Finding the cause helps guide treatment ^[5,6].

The cause may also show whether treatment must continue for life ^[5,6]. A detailed history often provides useful clues ^[5,6].

Low dietary intake of vitamin B12

Vitamin B12 occurs naturally mainly in foods from animals ^[3,9]. Common sources include:

• Meat ^[1,3]
• Poultry ^[1,3]
• Fish and shellfish ^[1]
• Eggs ^[1,3]
• Milk and dairy foods ^[1,3]
• Fortified breakfast cereals ^[1]

Fortified foods have vitamins or minerals added during production. They can help people who eat little or no animal food.

People with limited B12 intake may need fortified foods or supplements ^[1,2]. A diet review can help identify low intake ^[5,6].

However, diet is only one possible cause. Some people eat enough B12 but cannot absorb it well ^[3,8].

Pernicious anemia and digestive disorders

The stomach makes a protein called intrinsic factor ^[1,3]. This protein helps the body absorb vitamin B12 efficiently ^[1,3].

Absorption occurs in the last part of the small intestine ^[3]. Too little intrinsic factor can prevent normal B12 absorption ^[1,3].

Pernicious anemia is an autoimmune condition that affects intrinsic factor ^[2]. Autoimmune means the immune system attacks the body’s own tissues.

People with pernicious anemia cannot make enough intrinsic factor ^[2]. As a result, they have trouble absorbing vitamin B12 ^[2].

Autoimmune gastritis can also reduce intrinsic factor ^[5]. Gastritis means inflammation or damage in the stomach lining.

Other digestive diseases can interfere with vitamin B12 absorption ^[3,4]. A clinician may investigate these conditions when diet does not explain the deficiency ^[5,10].

Medicines, surgery, age, and nitrous oxide exposure

Surgery involving the stomach or intestines can raise the risk of deficiency ^[5,10]. These operations may change areas needed for normal B12 absorption.

Older adults also face a higher risk ^[2,10]. B12 deficiency affects between 3% and 43% of older adults ^[2].

The rate varies by the group studied and the test rules used ^[2]. Older adults with symptoms should discuss testing with a clinician ^[2,10].

Some medicines can increase risk when used for a long time ^[5,10]. Examples include metformin and proton pump inhibitors ^[5,10].

Metformin is commonly used to treat diabetes ^[10]. Proton pump inhibitors reduce the amount of acid made by the stomach ^[10].

Nitrous oxide exposure may also be important ^[5]. A clinician may ask about both medical and recreational exposure ^[5].

A full review should cover diet, medicines, surgery, and digestive disease ^[5,6]. It should also include nitrous oxide exposure when relevant ^[5].

Testing and Diagnosis

No single symptom can confirm vitamin B12 deficiency. Diagnosis combines the health history, examination, and blood test findings ^[5,6].

The goal is to confirm low B12 and identify its cause. Both steps can affect the treatment plan ^[5,6].

Who should be tested for vitamin B12 deficiency?

Routine screening is not advised for every adult ^[10]. Testing should be considered when symptoms occur with a known risk factor ^[7,10].

Possible reasons for testing include fatigue, depression, or thinking problems ^[5,10]. Numbness, neuropathy, and balance problems may also support testing ^[5,10].

Risk factors include limited intake, older age, and poor absorption ^[5,10]. Certain medicines and past digestive surgery also increase risk ^[5,10].

A clinician may ask when symptoms began. The clinician may also ask whether symptoms are getting worse.

An examination may check strength, feeling, balance, coordination, walking, and mental function ^[5,6]. These findings help guide the choice of tests ^[5,6].

Blood tests used to confirm deficiency

A complete blood count is often part of the evaluation ^[1,5]. It is commonly called a CBC.

A CBC measures red blood cells and other blood parts. It can identify anemia and changes linked with B12 deficiency ^[1,5].

Total or active vitamin B12 is commonly used as an initial test ^[5,7]. Active B12 is also called holotranscobalamin ^[5].

Active B12 measures the portion available to body cells ^[5]. A low total B12 level may support a diagnosis ^[6,10].

The result must still be reviewed with symptoms and risk factors ^[6]. Test ranges can also affect how a result is read ^[6].

An indeterminate result is unclear or near the test cutoff. More testing may be useful in this situation ^[5,7].

Elevated methylmalonic acid can support diagnosis when B12 results are indeterminate ^[5,7,10]. Methylmalonic acid is often shortened to MMA.

MMA rises when certain B12-dependent body processes cannot work normally ^[5,7]. This makes it useful when the first test is unclear ^[5,7,10].

Homocysteine can provide more support for the diagnosis ^[6]. However, it is less specific than MMA ^[6].

A borderline B12 result should be considered with the person’s symptoms ^[6]. This is especially important when nerve symptoms are present ^[5,6].

Tests that may identify the underlying cause

After confirming deficiency, the clinician may look for its source. Tests for intrinsic factor antibodies may support a pernicious anemia diagnosis ^[3].

Antibodies are proteins made by the immune system. Some antibodies can interfere with intrinsic factor or related stomach cells ^[3,10].

Further testing may check for autoimmune gastritis ^[5,10]. It may also look for other digestive conditions ^[5,10].

When the cause is unclear, testing may include an Helicobacter pylori test ^[10]. This bacterium can be linked with stomach disease ^[10].

The clinician should also review diet, medicines, and past surgery ^[5,6]. Medical history and lifestyle may provide important clues ^[5,6].

Nitrous oxide use should be discussed when it may apply ^[5]. This information can affect the testing approach ^[5].

Supplements can affect vitamin B12 test results. Tell the clinician about all supplements before testing ^[5].

Vitamin B12 Deficiency Treatment and Follow-Up

Treatment replaces vitamin B12 and addresses the cause ^[5,6]. The best method depends on symptoms, severity, and absorption ^[5,6].

Some people only need treatment for a limited period ^[5,6]. Others need long-term or lifelong B12 replacement ^[5,6].

Oral supplements, injections, and nasal therapy

Treatment may use oral tablets or vitamin B12 injections ^[2,6]. Prescription vitamin B12 nasal gel is another option ^[2].

High-dose oral vitamin B12 can work for some people with malabsorption ^[6,7]. Malabsorption means the digestive system cannot absorb nutrients well.

NICE advises at least one milligram daily for certain malabsorption cases ^[7]. This advice applies when oral replacement is chosen ^[7].

Injections may be preferred for severe symptoms or certain permanent causes ^[6,7]. They do not rely on absorption through the digestive system ^[2,6].

Clinicians may favor injections when serious nerve symptoms are present ^[6]. They may also use them when fast replacement is needed ^[6].

The treatment plan should match the person’s needs. Follow the prescribed product, dose, and schedule.

Do not create a personal injection plan. Medical guidance helps ensure that treatment fits the cause and severity ^[5,6].

Treating the cause and improving dietary intake

People with low intake may need more B12-rich foods ^[1,2]. Fortified foods can also provide vitamin B12 ^[1,2].

Useful sources include meat, poultry, fish, eggs, dairy foods, and fortified cereals ^[1,3]. Supplements may help when food intake remains too low ^[1,2].

Food changes alone may not fix a problem with absorption ^[2,3]. Pernicious anemia makes normal B12 absorption difficult ^[2].

People with permanent absorption problems may need lifelong replacement ^[5,6]. This group may include some people with pernicious anemia ^[2,5].

Lasting changes after digestive surgery may also require long-term replacement ^[5,6]. The exact plan depends on the person’s condition ^[5,6].

A clinician may review medicines that increase the risk of deficiency ^[5,10]. Do not stop a prescribed medicine without medical advice.

Recovery, monitoring, and prevention

Follow-up checks whether treatment is working ^[5,6]. It also helps find symptoms that have not improved ^[5,6].

Follow-up may include a symptom review and repeat blood tests ^[5,6]. The plan depends on the cause and treatment method ^[5,6].

Blood-related symptoms often improve with vitamin B12 replacement ^[6]. Nerve recovery may take longer ^[6].

Nerve damage can be incomplete or permanent when treatment is delayed ^[6]. This is one reason early medical assessment matters.

Long-term replacement can help prevent the deficiency from returning ^[5,6]. It may be needed while the underlying cause remains present ^[5,6].

People who avoid animal foods may need fortified foods or supplements ^[1,2]. These options can help maintain B12 intake ^[1,2].

Report new numbness, weakness, balance trouble, or thinking changes. Worsening symptoms may require another medical assessment ^[5,6].

Conclusion

Understanding vitamin B12 deficiency symptoms, causes, testing and treatment can support an earlier diagnosis. Prompt care may lower the risk of lasting nerve problems ^[6].

Vitamin B12 supports DNA production and healthy blood cells ^[3,4]. It is also needed for normal myelin and nerve function ^[3].

Deficiency can result from low intake or poor absorption ^[3,8]. Pernicious anemia, digestive surgery, medicines, and older age can increase risk ^[2,5,10].

Total or active B12 is usually the first laboratory test ^[5,7]. Elevated methylmalonic acid can help clarify an uncertain result ^[5,7,10].

Treatment may include oral B12, injections, nasal therapy, or dietary changes ^[2,6,7]. Some people with permanent absorption problems need lifelong replacement ^[5,6].

Anyone with symptoms or risk factors should seek medical testing. The right treatment depends on the cause, severity, and ability to absorb B12 ^[5,6].