Vitamin B12 Deficiency: Signs You Shouldn't Ignore

Vitamin B12 deficiency is easy to miss because its early signs look like ordinary life: you feel tired, a little foggy, maybe more short-tempered than usual. It tends to build slowly over months or even years, because the body stores enough B12 to cover a long gap before levels run low.

This piece walks through the signs, who is most at risk, and how the condition is tested and treated. It can help you decide whether to ask for a blood test, but it cannot diagnose you; only your doctor can do that.

What does vitamin B12 do in the body?

Vitamin B12 helps your body make healthy red blood cells, keeps your nerves working properly, and is needed to make DNA, the genetic material in every cell. Without enough of it, both your blood and your nervous system start to struggle.

According to the NIH Office of Dietary Supplements (ODS), most adults need 2.4 micrograms (mcg) a day, a little more during pregnancy (2.6 mcg) and breastfeeding (2.8 mcg). B12 is found naturally in animal foods such as meat, fish, eggs, and dairy, and it is added to some fortified foods like breakfast cereals and nutritional yeast.

B12 is one of many nutrients that a varied eating pattern covers without much effort, which is a theme that runs through the guide to nutrition and wellness. Problems usually come from the body failing to absorb B12, not only from eating too little of it.

What are the early signs of B12 deficiency?

The early signs are usually tiredness, weakness, and feeling short of breath with less effort than usual. These happen because low B12 can cause anemia, a shortage of healthy red blood cells to carry oxygen around the body.

The specific type is called megaloblastic anemia, meaning the red blood cells are larger than normal and do not work as well. MedlinePlus lists these common symptoms:

• Fatigue and low energy that does not improve with rest
• Pale or slightly yellow skin
• Shortness of breath or a racing heartbeat, especially during activity
• Dizziness or lightheadedness
• A sore, smooth, red tongue (called glossitis) or mouth ulcers
• Loss of appetite, weight loss, diarrhea, or constipation

Tiredness on its own has dozens of possible causes, from poor sleep to stress. If it is your main complaint, it helps to look at the wider list of reasons people feel tired all the time before assuming it is a vitamin.

Which signs suggest nerve damage?

Numbness, tingling, or a "pins and needles" feeling in your hands, feet, or legs is the sign most worth taking seriously. Low B12 can damage the nerves and the protective coating around them, and that damage can become permanent if it goes untreated for too long.

Other nervous system signs include:

• Trouble with balance or walking, especially in the dark
• Muscle weakness
• Memory problems, confusion, or trouble concentrating
• Changes in vision

These nerve symptoms can appear even when blood counts are still normal, so a normal blood count alone does not rule out B12 deficiency. That is one reason your doctor may order a specific B12 level rather than only a complete blood count.

Can low B12 affect your mood?

Yes, low B12 can be linked with mood changes such as low mood, irritability, and, in more severe cases, confusion or memory loss that can look like dementia in older adults. The NHLBI lists depression and confusion among the possible symptoms of B12 deficiency anemia.

That said, mood changes have many causes, and B12 is only one of them. If you have been feeling snappy and on edge, it can help to read about common causes of irritability alongside this piece, and to mention both your mood and any physical symptoms to your doctor at the same visit.

If you are feeling hopeless or having thoughts of harming yourself, call or text 988 to reach the 988 Suicide and Crisis Lifeline at any time.

How do B12 deficiency signs compare with iron deficiency?

B12 deficiency and iron deficiency both cause anemia, so they share tiredness, pale skin, and shortness of breath. The main difference is that B12 deficiency can also affect the nerves and brain, while iron deficiency usually does not.

Feature	Vitamin B12 deficiency	Iron deficiency
Tiredness and weakness	Common	Common
Pale skin	Common, sometimes slightly yellow	Common
Size of red blood cells	Larger than normal	Smaller than normal
Tingling or numbness in hands and feet	Common	Not typical
Balance or memory problems	Possible	Not typical
Sore, smooth tongue	Common	Possible
Craving ice or non-food items	Not typical	Possible
Usual food sources	Meat, fish, eggs, dairy, fortified foods	Meat, beans, lentils, leafy greens, fortified grains

Because the symptoms overlap, a blood test is the only reliable way to tell them apart, and some people have both at once. If iron is the concern, a list of everyday foods rich in iron shows how to cover it through meals.

Who is most at risk of B12 deficiency?

People at highest risk are those who cannot absorb B12 well and those who eat few or no animal foods. Absorption depends on stomach acid and a protein called intrinsic factor, so anything that affects the stomach or small intestine raises the risk.

Risk group	Why the risk is higher
Adults over 50	Many produce less stomach acid with age, which makes it harder to release B12 from food
People with pernicious anemia	An autoimmune condition stops the body making intrinsic factor, so B12 cannot be absorbed
Vegans and some vegetarians	B12 occurs naturally only in animal foods
People who have had weight-loss or stomach surgery	Parts of the stomach or intestine that absorb B12 may be bypassed or removed
People with celiac disease or Crohn's disease	Damage to the small intestine reduces absorption
Long-term users of metformin or acid-reducing drugs	These medicines can lower B12 absorption over time
Babies breastfed by mothers low in B12	The baby relies on the B12 in breast milk

Pernicious anemia, an autoimmune condition where the immune system attacks the cells that make intrinsic factor, is one of the most common causes in the US. It is not caused by diet, which is why eating more B12-rich food does not fix it.

What about medicines?

ODS notes that metformin, a common diabetes medicine, and acid-reducing drugs such as proton pump inhibitors (PPIs) and H2 blockers can reduce B12 absorption when taken for a long time. Do not stop a prescribed medicine on your own. Ask your doctor whether a periodic B12 check makes sense for you.

How do you get enough B12 from food?

Most people who eat meat, fish, eggs, or dairy get enough B12 from food. People who eat no animal foods need fortified foods or a supplement, according to the Dietary Guidelines for Americans.

Good sources include clams, beef, salmon, tuna, eggs, milk, yogurt, and cheese. For plant-based eaters, fortified breakfast cereals, fortified plant milks, and fortified nutritional yeast can help, but check the Nutrition Facts label, because not every product is fortified.

ODS also advises that adults over 50 get most of their B12 from fortified foods or supplements, because the synthetic form is easier to absorb when stomach acid is low. A whole-foods eating pattern can supply plenty of B12 if it includes animal foods, but a strictly plant-based version will need a fortified source.

How is B12 deficiency diagnosed?

B12 deficiency is diagnosed with blood tests ordered by your doctor. The usual starting point is a complete blood count (CBC), which measures your red blood cells, plus a vitamin B12 level.

If results are borderline, your doctor may order more specific tests:

• Methylmalonic acid (MMA): a substance that builds up in the blood when B12 is low
• Homocysteine: an amino acid that also rises when B12 or folate is low
• Intrinsic factor antibodies: a test for pernicious anemia

Taking folic acid supplements can correct the anemia caused by low B12 while the nerve damage continues, so tell your doctor about every supplement you take before testing.

How is B12 deficiency treated?

B12 deficiency is treated by replacing the vitamin, either with injections or with high-dose tablets, and by treating the underlying cause. Which one you get depends on why your levels are low and how severe the deficiency is.

People with pernicious anemia or major absorption problems often start with B12 shots, sometimes for life. People with milder deficiency, or a diet-related cause, may do well on high-dose oral supplements. Many symptoms, especially tiredness, improve within weeks; nerve symptoms can take longer and may not fully recover if damage has been present for a long time.

Do not self-treat suspected deficiency with supplements before testing. Starting B12 on your own can make a later diagnosis harder and may delay finding a cause like pernicious anemia.

When should you see a doctor or call 911?

See your doctor if you have ongoing tiredness, pale skin, a sore tongue, or any numbness or tingling in your hands or feet, especially if you are in a higher-risk group. Early testing matters because nerve damage from B12 deficiency can become permanent.

Make an appointment soon if you notice:

• Numbness, tingling, or burning in your hands or feet that does not go away
• New trouble with balance or walking
• Memory problems or confusion
• Tiredness lasting more than a few weeks
• You are vegan, pregnant, over 50, or take metformin or acid-reducing medicine and have any of the signs above

Call 911 or go to the emergency room for chest pain, severe shortness of breath, fainting, sudden weakness or numbness on one side of the body, sudden confusion, or trouble speaking. These can signal a stroke, heart problem, or severe anemia and need emergency care, whatever the cause turns out to be.