Written by Jillian Kubala, MS, RD — Medically reviewed by Meredith Goodwin, MD, FAAFP

Vitamin B12 is an essential nutrient that your body needs for processes, like DNA synthesis, energy production, and central nervous system function (1Trusted Source).

Even though the vitamin is found in many foods, B12 insufficiency and deficiency are relatively common. This is often due to limited dietary intake, malabsorption, certain medical conditions, or the use of B12-depleting medications (2Trusted Source3Trusted Source4Trusted Source).

In fact, studies suggest that up to 20% of people over the age of 60 in the United States and the United Kingdom are deficient in the vitamin (5Trusted Source).

For reference, B12 levels above 300 pg/mL are considered normal, levels of 200–300 pg/mL are considered borderline, and levels below 200 pg/mL are considered deficient (2Trusted Source).

Because the ability to absorb B12 from food declines with age, deficiency is more common in older adults. Still, that doesn’t mean children and younger adults, including those who are pregnant and breastfeeding, can’t develop B12 deficiency (5Trusted Source6Trusted Source).

Unfortunately, B12 deficiency is often overlooked and misdiagnosed. Oftentimes, this is due to inadequate laboratory testing or because the symptoms are not specific to vitamin B12 deficiency alone (7Trusted Source).

If you suspect you might have a B12 deficiency, it’s important to visit a healthcare professional to discuss your symptoms and undergo appropriate testing.

This article covers nine of the most commonly reported symptoms related to B12 deficiency and how this deficiency is diagnosed and treated.

1. Fatigue

If you’re low or deficient in B12, you’ll likely feel fatigued.

Your body’s cells need B12 to function properly. As such, having inadequate B12 levels can decrease normal red blood cell production, which can impair oxygen delivery (8Trusted Source).

Specifically, a deficiency in B12 or folate can cause megaloblastic anemia. This condition leads to the formation of large, abnormal, and immature red blood cells and impaired DNA synthesis (2Trusted Source9Trusted Source).

When your body doesn’t have enough healthy red blood cells to carry oxygen to tissues, you’ll likely feel weak and tired.

It’s important to know that you can develop fatigue and other symptoms related to B12 deficiency, even when your B12 levels are considered within range or only borderline low (6Trusted Source).

2. Pale or yellow skin

Another sign that can indicate B12 deficiency is pale or yellow skin.

Like the condition called iron deficiency anemia, anemia related to B12 deficiency may make your skin pale due to a lack of fully-matured, healthy red blood cells in the body (2Trusted Source).

B12 deficiency can also cause a condition called jaundice, which makes your skin and the whites of your eyes take on a yellowish color.

The color is caused by high levels of bilirubin, a waste product created when your body breaks down red blood cells (2Trusted Source).

3. Headaches

B12 insufficiency and deficiency can lead to neurological side effects, including headaches.

In fact, headaches are amongst the most commonly reported symptoms related to B12 deficiency in both adults and kids (2Trusted Source10Trusted Source11Trusted Source).

Some studies have shown that people who frequently experience certain types of headaches are more likely to have low B12 levels.

A 2019 study with 140 people, half of whom experienced migraines, found that blood levels of B12 were significantly lower in the participants with migraines compared with the participants with no migraine history (12Trusted Source).

The study also found that those with the highest B12 levels were 80% less likely to have migraines compared with participants with the lowest B12 levels (12Trusted Source).

Research continues to investigate if treatment with B12 may improve migraine headache symptoms in some people (13Trusted Source).

4. Depressive symptoms 

B12 is essential to the proper functioning of your central nervous system, and a deficiency in this nutrient can impact your mental health.

Specifically, B12 deficiency is associated with a greater risk of developing depression (14Trusted Source15Trusted Source).

Having low levels of B12 can cause elevated levels of a sulfur-containing amino acid called homocysteine. In turn, this may contribute to the development of depression by increasing oxidative stress, DNA damage, and cell death in the body (16Trusted Source17Trusted Source).

A 2020 study with 132 children and teens, 89 with and 43 without depression, found that the participants with depression had lower B12 levels and higher levels of homocysteine compared with those without depression (17Trusted Source).

In addition to depressive symptoms, low or deficient B12 levels may lead to other mental conditions, including psychosis and mood disorders (18Trusted Source).

5. Gastrointestinal issues 

A B12 deficiency may also cause diarrhea, nausea, constipation, bloating, gas, and other gastrointestinal symptoms (2Trusted Source19Trusted Source).

These issues can affect both adults and children (2Trusted Source20Trusted Source).

Keep in mind, though, that many of these symptoms are non-specific and could be caused by other factors. For example, food intolerances, medications, and infections could all lead to diarrhea.

6. Difficulty concentrating and mental impairment

Because a deficiency in B12 negatively impacts the central nervous system, people with low or deficient B12 levels may feel foggy-headed and have difficulty concentrating and completing tasks (21Trusted Source).

Older adults are especially at risk for these side effects because the risk of B12 deficiency increases with age.

In fact, many studies have associated low B12 levels with worsened mental function in older adults (22Trusted Source23Trusted Source).

Fortunately, studies show that mental impairment related to low B12 levels can improve with B12 treatment.

For example, a 2020 study gave 202 people with mild mental impairment and low or low-normal B12 levels and elevated homocysteine levels B12 replacement therapy for 3 months (21Trusted Source).

After the treatment, 84% of the participants reported significant improvements in symptoms, like poor focus, memory decline, and forgetfulness (21Trusted Source).

7. Pain and inflammation of the mouth and tongue 

Glossitis is a medical term that refers to an inflamed, red, and painful tongue. It can be caused by a B12 deficiency (24Trusted Source).

In people with this deficiency, glossitis can appear alongside stomatitis, which is characterized by sores and inflammation in the mouth (25Trusted Source).

Even though glossitis and stomatitis are common in people with B12 deficiency-related anemia, they can also occur without anemia and can be a sign of an early B12 deficiency (25Trusted Source).

That being said, glossitis can also be caused by deficiencies in other nutrients, like folate, riboflavin (B2), and niacin (B3) (25Trusted Source).

8. Paresthesia in hands and feet

Paresthesia is a medical term that refers to a burning or pins-and-needles sensation in certain areas of the body, like the hands and feet.

Many adults and kids who have B12 deficiency report experiencing paresthesia (7Trusted Source20Trusted Source).

Unfortunately, this symptom of B12 deficiency overlaps with symptoms related to diabetic neuropathy — nerve damage caused by high blood sugar that can cause pain and numbness in the extremities (26Trusted Source).

People with diabetes taking metformin are at a higher risk of developing B12 deficiency, because this medication can reduce vitamin B12 absorption in the body (4Trusted Source).

So, a B12 deficiency could be misdiagnosed as peripheral neuropathy in people with diabetes.

As a result, many experts recommend that people taking metformin regularly get screened for vitamin B12 deficiency.

9. Other signs and symptoms of B12 deficiency 

In addition to the symptoms above, B12 deficiency may lead to the following:

  • Muscle cramps and muscle weakness. B12 deficiency negatively impacts motor and sensory nerve function, which can cause muscle cramps and weakness (7Trusted Source27Trusted Source).
  • Impaired coordination. Ataxia, or impaired balance and coordination, is a neurological symptom that can be caused by B12 deficiency. As such, a person with B12 deficiency may have difficulty walking and balancing (2Trusted Source).
  • Erectile dysfunction. Men with B12 deficiency may experience erectile dysfunction as a result of increased levels of homocysteine in the body (28Trusted Source).
  • Vision disturbances. B12 deficiency may cause vision disturbances, possibly due to damage to the optic nerve (29Trusted Source)

How is B12 deficiency detected and treated?

Because vitamin B12 deficiency symptoms aren’t specific to the condition, it may go undetected or get misdiagnosed.

If you’re experiencing any of the symptoms listed above, it’s important to discuss them with a healthcare professional.

This is especially relevant if you:

  • follow a restrictive diet, like a vegan diet
  • are over the age of 60
  • are pregnant or breastfeeding
  • have a medical condition that can deplete B12 levels
  • take a B12-depleting medication, like metformin or proton pump inhibitors

In addition to learning about your symptoms and giving you a physical exam, a healthcare professional can rule out a B12 deficiency by ordering blood tests.

These tests can include (2Trusted Source):

  • B12 levels
  • folate levels
  • a complete blood count (CBC) with a peripheral smear
  • methylmalonic acid (MMA) levels
  • homocysteine levels

If you’re diagnosed with too low B12 levels, your healthcare professional will recommend the most appropriate treatment. It may include B12 injections, oral B12 supplements, or addressing an underlying health condition that could be causing the deficiency (2Trusted Source).

B12 injections are generally recommended for people who can’t properly absorb B12 from food or supplements, like those who’ve undergone gastric bypass surgery or people with certain autoimmune diseases (2Trusted Source).

B12 supplements and injections are considered safe and well-tolerated, even in large doses (1Trusted Source).


If your healthcare professional thinks you may be low in B12, they’ll order appropriate blood tests to assess your B12 levels. Treatment of B12 deficiency typically includes oral supplements or injections.

The bottom line

B12 deficiency can cause a variety of symptoms, including fatigue, headaches, depression, pale or yellow skin, mental impairment, and pain and inflammation in the mouth and tongue.

Many of the symptoms caused by low B12 levels are not specific to B12 deficiency, which can cause the condition to go undetected.

If you’re experiencing any of the symptoms listed above, it’s important to visit a healthcare professional to undergo appropriate testing and get the right treatment.

Just one thing

Try this today: If you’re low or deficient in B12, your healthcare professional will likely recommend an oral supplement or injections.

Additionally, if low dietary intake is the cause, increasing your intake of B12-rich foods, like fish and shellfish, organ meats, and eggs, is a good idea.

If you follow a vegan or vegetarian diet, enjoying B12 fortified foods, like nutritional yeast and plant milk, and taking a B12 supplement can help you maintain optimal levels.

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