Vitamin B12 is an essential nutrient involved in red blood cell formation, DNA production, and normal nervous-system function. Because the body can store substantial amounts of B12, deficiency may develop gradually, and symptoms can sometimes be overlooked or mistaken for ordinary tiredness or aging.

Recognizing possible warning signs is important because untreated vitamin B12 deficiency can cause neurological problems that may become permanent. At the same time, these symptoms can have many other causes, so symptoms alone cannot confirm a deficiency. A healthcare professional can usually investigate with a blood test and, when appropriate, additional testing.

Here are four symptoms worth discussing with a healthcare professional.

1. Persistent or Unusual Fatigue

One of the most common symptoms associated with vitamin B12 deficiency is fatigue or unusual weakness.

Vitamin B12 is needed for healthy red blood cell production. When deficiency interferes with red blood-cell formation, it can contribute to anemia. With fewer healthy red blood cells available to transport oxygen, a person may feel unusually tired, weak, lightheaded, or short of breath during activity.

This isn’t the same as simply feeling sleepy after a busy day.

Possible signs include:

• Persistent tiredness
• Reduced energy
• General weakness
• Dizziness or lightheadedness
• Shortness of breath with exertion
• Pale-looking skin
• Heart palpitations

However, fatigue is extremely common and can result from iron deficiency, thyroid disorders, inadequate sleep, infections, medications, stress, and numerous other conditions.

If fatigue persists without an obvious explanation, testing can help identify the cause.

2. Numbness, Tingling, or “Pins and Needles”

Neurological symptoms are particularly important because vitamin B12 plays a role in maintaining healthy nerve function.

A deficiency can cause abnormal sensations known as paresthesia. People may describe these sensations as:

• Tingling
• Pins and needles
• Numbness
• Burning sensations
• Reduced sensitivity
• An unusual feeling in the hands or feet

These symptoms may begin subtly and can gradually become more noticeable.

Some people initially assume they have simply slept on an arm or sat in an awkward position. Occasional temporary tingling is common, but persistent or recurring numbness and tingling deserve medical attention, particularly when there is no obvious explanation.

Long-standing B12 deficiency can damage nerves, and neurological complications may sometimes persist even after treatment. That’s one reason early evaluation matters.

3. Balance or Walking Problems

As neurological effects progress, some people with B12 deficiency may develop problems with coordination, balance, or walking.

You might notice:

• Feeling unsteady while walking
• Difficulty maintaining balance
• Frequent stumbling
• Muscle weakness
• Changes in coordination
• A feeling that your legs aren’t working normally

These symptoms should not automatically be blamed on vitamin B12 deficiency.

Balance problems can also be caused by neurological disorders, inner-ear conditions, medication effects, vision problems, spinal conditions, and other nutritional deficiencies.

Nevertheless, unexplained changes in walking or balance warrant medical evaluation, especially if they are new or progressively worsening.

4. A Sore, Smooth, or Inflamed Tongue

Another possible sign of B12 deficiency is glossitis, an inflammation of the tongue.

The tongue may appear unusually:

• Red
• Smooth
• Swollen
• Tender

Some people experience burning or soreness, and eating spicy or acidic foods may become uncomfortable.

Mouth-related symptoms can sometimes appear alongside other signs of nutritional deficiency.

However, a sore tongue isn’t specific to vitamin B12 deficiency. Iron deficiency, folate deficiency, infections, irritation, medications, and other conditions can produce similar symptoms.

That’s why persistent mouth changes should be evaluated rather than automatically attributed to B12.

Other Possible Symptoms

The four symptoms above aren’t the only possible signs.

Vitamin B12 deficiency may also be associated with:

• Pale or yellowish skin
• Headaches
• Reduced appetite
• Weight loss
• Muscle weakness
• Vision changes
• Cognitive difficulties
• Memory problems
• Mood changes

Some people can have neurological symptoms even without obvious anemia, which is another reason symptoms should be considered in context rather than relying only on blood counts.

Who Is More Likely to Develop B12 Deficiency?

Vitamin B12 occurs naturally in foods such as meat, fish, eggs, dairy products, and other animal-derived foods. Some foods are also fortified with B12.

Certain groups have a higher risk of deficiency.

People Following Vegan Diets

Unfortified plant foods generally don’t provide reliable amounts of naturally occurring vitamin B12. People following a vegan diet therefore need a dependable source from fortified foods or supplements.

Older Adults

The ability to absorb B12 from food can decrease with age, partly because of changes affecting stomach acid and digestion.

People With Certain Digestive Conditions

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

People Who Have Had Certain Gastrointestinal Surgeries

Some surgeries involving the stomach or intestines can reduce the body’s ability to absorb vitamin B12.

People Taking Certain Medications

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

This doesn’t mean you should stop prescribed medication. Instead, discuss B12 monitoring with your healthcare professional if you have risk factors.

How Is Vitamin B12 Deficiency Diagnosed?

Symptoms alone aren’t enough to diagnose B12 deficiency.

A healthcare professional may order a blood test for vitamin B12, along with a complete blood count and other tests depending on the situation.

If the B12 result is borderline but symptoms or risk factors are present, additional markers such as methylmalonic acid (MMA) and homocysteine may sometimes help clarify whether deficiency is present.

The appropriate testing depends on the individual.

Why Early Treatment Matters

The good news is that vitamin B12 deficiency is generally treatable.

Treatment depends on why the deficiency developed.

For some people, dietary changes or oral B12 supplements may be sufficient. Others may require higher-dose supplementation or injections, particularly when absorption is impaired.

Treatment should address the underlying cause as well as the low B12 level.

The earlier deficiency-related neurological problems are recognized, the better the chance of preventing lasting nerve damage.

Foods That Provide Vitamin B12

If your diet includes animal products, useful sources include:

• Beef
• Chicken
• Fish
• Shellfish
• Eggs
• Milk
• Yogurt
• Cheese

Fortified foods can also provide B12, including certain breakfast cereals and plant-based milk alternatives.

People who don’t consume animal products should pay particular attention to reliable fortified foods or appropriate supplementation.

When Should You Seek Medical Advice?

Make an appointment with a healthcare professional if you have persistent unexplained fatigue, recurring numbness or tingling, balance problems, or ongoing tongue or mouth changes.

Seek urgent medical attention for sudden weakness, sudden numbness, severe difficulty walking, confusion, fainting, chest pain, severe shortness of breath, or other sudden neurological symptoms. These can have causes that require immediate evaluation and should not simply be assumed to be a vitamin deficiency.