4 Common Symptoms of Vitamin B12 Deficiency You Should Know

Vitamin B12 plays an important role in keeping the body functioning properly. It helps support healthy red blood cells, normal nerve function, and DNA production. When the body doesn’t get or absorb enough vitamin B12, a deficiency can develop and may eventually affect multiple systems in the body.

One challenge with vitamin B12 deficiency is that its symptoms can develop gradually. Some people may initially notice subtle changes such as unusual tiredness, while others may experience tingling, weakness, or changes in concentration.

Knowing the common symptoms of vitamin B12 deficiency can help you recognize when it may be worth talking with a healthcare professional. Symptoms alone, however, cannot confirm a deficiency because many other health conditions can cause similar problems.

Here are four common signs to know about.

What Is Vitamin B12?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that the body needs for several important functions.

It is involved in:

• Red blood cell formation
• DNA synthesis
• Normal nervous-system function
• Maintaining healthy nerve cells
• Supporting normal energy metabolism

Vitamin B12 is naturally found primarily in animal-derived foods, including fish, meat, poultry, eggs, and dairy products. Some foods, such as certain breakfast cereals and plant-based milk alternatives, may also be fortified with vitamin B12.

The body can store vitamin B12 for a relatively long time, so deficiency doesn’t necessarily develop immediately when intake decreases.

1. Unusual Fatigue and Weakness

One of the most commonly recognized symptoms associated with vitamin B12 deficiency is persistent tiredness or weakness.

Vitamin B12 is needed for healthy red blood cell production. A significant deficiency can contribute to megaloblastic anemia, a condition in which red blood cells are larger than normal and don’t function normally.

When anemia develops, the body may have difficulty delivering enough oxygen to tissues. This can contribute to symptoms such as:

• Fatigue
• Weakness
• Low energy
• Lightheadedness
• Shortness of breath, particularly with exertion
• Pale-looking skin

It’s important to remember that fatigue is extremely common and has many possible causes. Poor sleep, stress, dehydration, certain medications, infections, iron deficiency, thyroid problems, and other medical conditions can all contribute to tiredness.

If fatigue is persistent, severe, or unexplained, a healthcare professional can help determine the underlying cause.

2. Tingling, Numbness, or Other Nerve Changes

Vitamin B12 is particularly important for normal neurological function.

A deficiency can affect the nervous system and may cause sensations such as tingling or numbness, especially in the hands and feet.

Some people describe the sensation as:

• Pins and needles
• Burning
• Reduced sensitivity
• Electric or prickling sensations
• Numbness in the hands or feet

Balance and coordination can also be affected in more advanced cases.

Neurological symptoms deserve attention because prolonged vitamin B12 deficiency can potentially cause nerve damage. Some neurological problems may persist even after treatment if a deficiency has been present for a long time.

That doesn’t mean tingling automatically indicates a B12 deficiency. Diabetes, nerve compression, alcohol use, certain medications, nutritional deficiencies, and other neurological conditions can cause similar symptoms.

For that reason, unexplained or persistent numbness or tingling should be evaluated rather than self-diagnosed.

3. Changes in Thinking, Concentration, or Mood

Another possible sign of vitamin B12 deficiency involves cognitive or psychological changes.

Some people with deficiency may experience:

• Difficulty concentrating
• Forgetfulness
• Confusion
• Irritability
• Changes in mood
• Feeling mentally “foggy”

These symptoms can be subtle, particularly when a deficiency develops slowly.

Vitamin B12 is involved in normal neurological function, so inadequate levels can affect the nervous system. However, changes in concentration or mood have many possible explanations, including inadequate sleep, stress, anxiety, depression, medications, hormonal changes, and other health conditions.

If cognitive or mood changes are new, persistent, or interfering with everyday life, it’s important to discuss them with a healthcare professional.

Sudden confusion or significant changes in mental status require prompt medical evaluation.

4. Changes in the Mouth and Tongue

Vitamin B12 deficiency can sometimes cause noticeable changes in the mouth.

A person may develop a sore, swollen, smooth, or unusually red tongue. Some people may also experience mouth discomfort, burning sensations, or recurrent mouth sores.

These symptoms can make eating less comfortable and may occur alongside other deficiency symptoms.

Because oral symptoms have many possible causes, they aren’t specific to vitamin B12 deficiency. Dental problems, infections, irritation, allergies, and other nutritional deficiencies can also produce mouth or tongue changes.

Still, persistent unexplained changes are worth discussing with a healthcare professional, particularly if they occur alongside fatigue, weakness, or neurological symptoms.

Other Possible Symptoms of Vitamin B12 Deficiency

The four symptoms above are among the better-known signs, but vitamin B12 deficiency can involve other symptoms as well.

Depending on the severity and individual circumstances, a person may experience:

• Reduced appetite
• Weight loss
• Heart palpitations
• Shortness of breath
• Headaches
• Dizziness
• Pale skin
• Muscle weakness
• Problems with balance
• Vision changes in some cases

Not everyone with a deficiency experiences the same symptoms.

Some people may have laboratory evidence of low vitamin B12 before they notice obvious symptoms, while others may develop neurological symptoms with or without significant anemia.

Who May Be at Risk of Vitamin B12 Deficiency?

Certain people have a higher risk of developing inadequate vitamin B12 levels.

People Following Vegan or Strict Plant-Based Diets

Vitamin B12 occurs naturally in significant amounts mainly in animal-derived foods. People who avoid all animal products may therefore need reliable sources of fortified foods or vitamin B12 supplements.

The appropriate amount and form of supplementation can vary, so discussing nutritional needs with a qualified healthcare professional or registered dietitian can be helpful.

Older Adults

As people age, changes in stomach acid production and other digestive factors can make it harder for the body to absorb vitamin B12 from food.

People With Certain Digestive Conditions

Conditions affecting the stomach or small intestine can interfere with vitamin B12 absorption.

Certain gastrointestinal surgeries can also affect how the body obtains B12 from food.

People Taking Certain Medications

Some medications can interfere with vitamin B12 absorption or metabolism. Long-term use of certain acid-reducing medicines and metformin, for example, has been associated with lower vitamin B12 levels in some people.

If you take medication regularly, don’t stop or change it because of a suspected vitamin deficiency. Instead, discuss concerns with your healthcare professional.

How Is Vitamin B12 Deficiency Diagnosed?

Symptoms alone aren’t enough to diagnose vitamin B12 deficiency.

A healthcare professional may consider your medical history, diet, medications, symptoms, and physical examination before ordering blood tests.

Testing may include a measurement of vitamin B12 levels along with a complete blood count. Depending on the situation, additional tests may be used to investigate borderline results or determine why a deficiency is occurring.

This is important because treatment works best when the underlying cause is identified.

For example, someone may have inadequate dietary intake, while another person may consume enough B12 but have difficulty absorbing it.

Why You Shouldn’t Ignore Neurological Symptoms

Fatigue can have many causes, but neurological symptoms such as persistent numbness, tingling, balance problems, or weakness deserve particular attention.

Vitamin B12 deficiency can affect the nervous system, and delayed diagnosis may increase the risk of lasting neurological problems.

If you develop unexplained neurological symptoms, particularly if they are getting worse, seek medical advice rather than assuming that a vitamin supplement will solve the problem.

Can You Prevent Vitamin B12 Deficiency?

For many people, getting enough vitamin B12 through a balanced diet is straightforward.

Good dietary sources include:

• Fish
• Meat
• Poultry
• Eggs
• Milk and other dairy products
• Vitamin B12-fortified foods

People who don’t consume animal products may need to pay particular attention to fortified foods or supplementation.

Prevention also means addressing absorption problems when they exist. Simply consuming more B12 may not correct a deficiency if an underlying medical condition prevents adequate absorption.

Should You Take a Vitamin B12 Supplement?

A B12 supplement can be useful for people who are deficient or at increased risk, but supplementation isn’t automatically necessary for everyone.

If you suspect you have a deficiency, it’s better to discuss testing and treatment with a healthcare professional.

High-dose supplements are widely available, but “more” isn’t necessarily better. The appropriate approach depends on the reason for the deficiency and how severe it is.

People with absorption problems may require a different treatment strategy from those whose deficiency is caused by inadequate dietary intake.

When Should You Talk to a Doctor?

Consider seeking medical advice if you have persistent or unexplained symptoms such as:

• Ongoing fatigue or weakness
• Numbness or tingling
• Problems with balance
• Unexplained changes in memory or concentration
• Persistent tongue or mouth changes
• Shortness of breath or dizziness
• Multiple symptoms occurring together

You should seek urgent medical attention for severe breathing difficulty, fainting, sudden confusion, sudden weakness, or other symptoms that could indicate an emergency.

The Bottom Line

Vitamin B12 is essential for healthy blood cells and normal nervous-system function. A deficiency can develop gradually, making the early warning signs easy to overlook.

The four common symptoms of vitamin B12 deficiency discussed here are unusual fatigue or weakness, numbness or tingling, cognitive or mood changes, and changes affecting the tongue or mouth.

However, these symptoms aren’t unique to B12 deficiency. Many other conditions can cause similar problems, so symptoms alone shouldn’t be used to diagnose yourself.

If you have persistent, unexplained, or worsening symptoms—or if you’re in a group at higher risk for B12 deficiency—talk with a healthcare professional. Appropriate testing can help determine whether vitamin B12 levels are actually low and identify the reason if a deficiency is present.

Taking symptoms seriously without jumping to conclusions is the best approach: know the signs, seek appropriate testing, and treat the underlying cause rather than relying on guesswork.