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Vitamin B12 Deficiency: Symptoms, Causes, And More

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is necessary to maintain healthy functioning of the body (1). As one of eight essential B vitamins that are necessary for many functions, most Americans consume adequate amounts of B12. However, some people have difficulty absorbing it and are at risk of deficiency (2), (3).

Essential B vitamins like vitamin B12 are vital to maintaining many functions throughout the body. Other factors can contribute to low B12 levels as well. These can include age, digestion issues, diet, and medication use (2), (4), (5), (6) (7).

Vitamin B12 and B9 (folate) are particularly vital for methylation to occur throughout the body, too. Without methylation, cells throughout the body cannot function properly (8), (9).

Summary: Vitamin B12 is one of the 8 essential B vitamins. It is a water-soluble vitamin that is helpful for cellular formation, nerve functioning, and energy production. Age, digestive issues, diet, and medication use can affect vitamin B12 absorption.

Signs and Symptoms of Vitamin B12 Deficiency

Are you getting enough vitamin B12 in your daily diet? Find out more about some common symptoms of vitamin B12 deficiency, causes, and the best foods to eat to boost your levels and promote more healing throughout the body.

1. Lack of Energy or Lethargy

One of the symptoms of vitamin B12 deficiency is low energy, fatigue or lethargy (2). When you are critically low in vitamin B12, it can be hard to even get out of bed in the morning.

Energy production and essential B vitamins go hand in hand, especially vitamin B12. There is some evidence that if you are deficient in vitamin B12, supplementing may improve your energy levels (10).

Read on to find out what common disorders can bring up vitamin B12 deficiencies.

Summary: Low energy, fatigue, or lethargy are common vitamin B12 deficiency symptoms. Supplementing with vitamin B12 may help improve energy levels, especially if you are deficient.

2. Poor Cognitive Development and Depression

Proper brain development in pregnancy, infancy and childhood depends on getting adequate levels of B12, among many other factors (11). That is why pregnant women need to take a multivitamin high in B12 and folate (B9) (12).

There is increased risk that a child who was lacking B12 in infancy develops depression later in life (13).

Depressive symptoms can vary per person. Those who suffer from depression can have psychological trauma, so nutrition is only one factor to consider as the cause of depressive disorders (14).

Summary: Vitamin B12 is needed for proper brain development during pregnancy, infancy, and childhood. It also contributes to development of depression or depressive disorders. Make sure to consume vitamin B12-rich foods to nourish your brain health.

3. Megaloblastic Anemia

Vitamin B12 is needed in the normal production of new red blood cells (2). Megaloblastic anemia occurs when the red blood cells are too large, and there is not enough present in the bloodstream (15). A common sign of vitamin B12 deficiency is megaloblastic anemia (16).

Blood tests can diagnose megaloblastic anemia (17). Taking adequate levels of B12 through food or supplementation can prevent this from happening.

Summary: Megaloblastic anemia occurs when red blood cells are too large and there is not enough present in the bloodstream, which is a common sign of vitamin B12 deficiency. Blood tests are done to diagnose this.

4. Memory Loss

Just as low B12 can lead to declined cognitive development and depression, it also plays a significant role in memory production. Memory loss, disorientation, and dementia are possible symptoms of vitamin B12 deficiency (2), (18).

Memory loss does not include cognitive decline like dementia or Alzheimer’s disease. There is currently not enough evidence to support that B12 is a helpful supplement for those who already have memory loss diseases (19).

Because vitamin B12 deficiency causes memory loss and other symptoms of dementia, there is some evidence that vitamin B12 deficiency may be one potential cause of some cases of dementia in the elderly (20).

If you are having trouble with retaining information lately, speak to your healthcare professional about getting tested for vitamin B12 deficiency.

Summary: Low vitamin B12 can lead to cognitive decline and depression, including memory loss. However, for those who already have memory loss diseases such as Dementia or Alzheimer’s, supplementation has not been shown to be helpful.

5. Swollen Tongue and Mouth Pain

Tongue pain or a swollen tongue can occur from vitamin B12 deficiency as well. Others can include a burning sensation in the mouth, and mouth ulcers (2), (18), (21).

Essential B vitamins, especially vitamin B12, are vital to maintaining a healthy mouth, as well as energy production, and much more.

Summary: A swollen tongue, mouth pain, burning sensation in the mouth, or mouth ulcers are common side effects of low vitamin B12.

6. Nerve Problems

Vitamin B12 deficiency or insufficiency can often present itself as nerve problems (2). That includes potential symptoms of tingling in the hands and feet, trouble walking, and nerve pain.

A “pins and needles” or numbing sensation is typical for those who have a vitamin B12 deficiency, as it indicates a sign of nerve issues. Neurons require ample amounts of vitamin B12 to function (22).

Myelin, a substance that coats nerve endings, can be low in those with B12 deficiency (23). Without enough myelin, nerve problems can persist.

Summary: Nerve problems such as tingling hands and feet, trouble walking, or nerve pain, are common for those with vitamin B12 deficiency. Neurons require vitamin B12 to function. Myelin, which is a substance that coats nerve endings, can be lacking for those with vitamin B12 deficiency.

7. Fast Heart Rate or Tachycardia

A fast heart rate or tachycardia can occur from B12 deficiency because of megaloblastic anemia caused by B12 deficiency (24).

As explained above, megaloblastic anemia is when the red blood cells are too large, causing dizziness, fatigue, and loss of appetite.

Make sure to have your doctor or healthcare professional check you for megaloblastic anemia if you suffer from a fast heart rate or tachycardia.

Summary: Vitamin B12 deficiency can cause megaloblastic anemia, which then causes tachycardia, or a fast heart rate, to occur. Megaloblastic anemia also causes dizziness, fatigue, and loss of appetite.

Causes of Vitamin B12 Deficiency

Vitamin B12 deficiency is more common than other B vitamin deficiencies because it stems from multiple reasons. For the most part, many can become deficient in B12 because of malabsorption, malnutrition, or autoimmunity (25).

Factors that can affect your chance of becoming deficient in vitamin B12 include (2):

  • Age
  • Malnutrition or maldigestion
  • Autoimmune conditions such as pernicious anemia
  • Crohn’s disease
  • Past surgery on the stomach or digestive system
  • Inadequate intake of Vitamin B12 foods in your diet
  • Low stomach acid
  • Strict vegan or vegetarian diet

If you take suffer from one of the following issues, conditions, or disorders, you are more likely to be at risk of vitamin B12 deficiency (26), (27). Be sure to speak with your doctor or healthcare professional if you suspect you may be low in vitamin B12.

You can easily ask to receive blood work to check your vitamin B12 levels, as well as all essential B vitamins, to get to the root cause of the disease or malfunction in your body.

Summary: Malabsorption, malnutrition, or autoimmune issues can cause vitamin B12 deficiency. Other factors include age, inflammatory bowel issues, surgery on the digestive tract, low stomach acid, or a strict vegan or vegetarian diet. Check your blood levels if you have experienced any of these common causes.

Foods that Contain Vitamin B12

Many foods are high in vitamin B12, although they mostly come from animal sources. Check out the list below to see where you can start adding more foods high in vitamin B12 to your diet today.

Foods that contain vitamin B12 include (2), (28), (29):

  • Clams
  • Beef liver
  • Trout
  • Tuna
  • Nutritional yeast (a great option for vegans)
  • Beef
  • Haddock
  • Milk
  • Yogurt
  • Cheese
  • Fortified cereals
  • Ham
  • Eggs
  • Chicken

As you can see, most of these B12 foods are animal-based products. Some vegans and vegetarians are at higher risk of B12 deficiency (30). Depending on the variety and adequacy in the diet, some vegans and vegetarians may require supplements.

Remember that Vitamin B12 is water-soluble, so it is rare to take too much through food or supplementation (31).

If you suspect you are low in vitamin B12, be sure to speak with your doctor about testing your blood levels. Essential B vitamins like vitamin B12 are vital to maintaining energy, red blood cell production and more.

Summary: Many animal-based foods contain vitamin B12, such as clams, beef liver and meat, tuna, salmon, ham, chicken, dairy products, or eggs. There are some plant-based foods with vitamin B12, such as fortified cereals or nutritional yeast. However, if you follow a vegan or vegetarian diet, you may need to take a vitamin B12 supplement.


Vitamin B12 deficiency is one of the more common B vitamin deficiencies. Many do not get an adequate intake of this crucial vitamin because of malabsorption, maldigestion, a poor diet, and more.

With a healthy, balanced diet, you may be able to get adequate levels of vitamin B12 and avoid any of these unnecessary symptoms. However, if you eat well, and still suffer from any of the above symptoms, talk to your doctor or healthcare professional about checking your vitamin B12 level.