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What is Vitamin B12 and What Are the Symptoms of Vitamin B-12 Deficiency?

Vitamin B-12 is an essential nutrient that keeps the body functioning properly. Symptoms of vitamin B-12 deficiency include fatigue, low mood, and nerve problems.

What is vitamin B12?

First of all, the term vitamin is used to describe compounds that are essential for normal function but cannot be synthesized by the human body. They must, therefore, be acquired from the diet—or nowadays via pills known as supplements.

Vitamin B12 belongs to a family of naturally occurring cobalt-containing compounds known as cobalamins. It was discovered in the late 1940s about a decade and a half after it was determined that consumption of liver corrected a particular type of anemia known as pernicious anemia.

Eventually, the vitamin was purified and crystallized from liver and its structure was elucidated via x-ray crystallography. This led, in 1973, to the vitamin being synthesized (created artificially). This, in turn, opened up the possibility of using supplements to remedy deficiencies of the vitamin.

What type of foods contain vitamin B12?

Vitamin B12 can only be found in animal products (e.g., fish, meat, eggs, and dairy products). It is generally not present in foods that come from plants. However, it can be found in many breakfast cereals, nutritional yeasts, and other foods that have been fortified with B12.

Vitamin B12 can be found in varying amounts in almost all animal foods. However, certain animal foods, such as liver and clams, contain particularly large amounts. The National Institutes of Health Office of Dietary Supplements provides a list of the amount of B12 found in a variety of foods. Here are some examples:

  • 3 ounces of cooked clams contain 84.1 mcg of B12 or 3,504% of the recommended Daily Value (DV)
  • 3 ounces of cooked beef liver contains 70.72 mcg or 2,946% of DV
  • 3 ounces of sockeye salmon has 4.8 mcg (200% of DV)
  • A double patty cheeseburger with bun has 2.1 mcg of B12 or 88% of DV.
  • 1 hard-boiled has 0.6 mcg or 25% of DV
  • 1 cup of low-fat mild contains 1.2 mcg of B12 or 50% of DV

The human body does not create vitamin B-12, so people must get this nutrient from their diet. It is crucial for making DNA and red blood cells, and it helps support the nervous system.

Vitamin B-12 plays a vital role in the production of blood cells.

Many of the symptoms of vitamin B-12 deficiency arise because it causes a lack of healthy blood cells. The body needs plenty of these cells to get oxygen around the body and keep the organs in good health.

A vitamin B-12 deficiency can lead to both physical and psychological problems. In this article, we explore 11 symptoms of vitamin B-12 deficiency and explain why they occur.

What to know about vitamin B-12 deficiency

Vitamin B-12 deficiency may affect between 1.5 and 15.0 percent of people.

This deficiency can cause a wide range of symptoms that affect a person’s mental and physical health.

It is important to consume foods that contain vitamin B-12 on a regular basis. Adults need around 2.4 micrograms (mcg) of vitamin B-12 each day.


Vitamin B-12 is a water-soluble vitamin that is present in animal-based foods, such as:

  • red meat
  • poultry
  • eggs
  • dairy
  • fish

If a person does not eat animal products, they will need to add vegetarian and vegan sources of vitamin B-12 to their diet. These include fortified cereals, plant milks, bread, and nutritional yeast.

As vitamin B-12 deficiency shares many symptoms with other nutritional deficiencies and health conditions, it is possible that people may neither notice it nor get a diagnosis.

Being aware of all of the signs can help people identify the deficiency and seek treatment.

Below, we look at the symptoms of vitamin B-12 deficiency and their causes.

1. Tingling hands or feet

Vitamin B-12 deficiency may cause “pins and needles” in the hands or feet. This symptom occurs because the vitamin plays a crucial role in the nervous system, and its absence can cause people to develop nerve conduction problems or nerve damage.

In the nervous system, vitamin B-12 helps produce a substance called myelin. Myelin is a protective coating that shields the nerves and helps them transmit sensations.

People who are vitamin B-12 deficient may not produce enough myelin to coat their nerves. Without this coating, nerves can become damaged.

Problems are more common in the nerves in the hands and feet, which are called peripheral nerves. Peripheral nerve damage may lead to tingling in these parts of the body.

2. Trouble walking

Over time, peripheral nerve damage resulting from vitamin B-12 deficiency can lead to movement problems.

Numbness in the feet and limbs may make it hard for a person to walk without support. They may also experience muscle weakness and diminished reflexes.

3. Pale skin and lost Hair

Pale or yellow skin, called jaundice, may be a symptom of vitamin B-12 deficiency.

Jaundice develops when a person’s body is not able to produce enough red blood cells. Red blood cells circulating under the skin provide it with its normal color. Without enough of these cells, the skin may look pale.

Vitamin B-12 plays a role in the production of red blood cells. A vitamin B-12 deficiency can cause a lack of red blood cells, or megaloblastic anemia, which has an association with jaundice.

This type of anemia can also weaken the red blood cells, which the body then breaks down more quickly. When the liver breaks down red blood cells, it releases bilirubin. Bilirubin is a brownish substance that gives the skin the yellowish tone that is characteristic of jaundice.

4. Fatigue

Megaloblastic anemia due to vitamin B-12 deficiency may lead to a person feeling fatigued.

Without enough red blood cells to carry oxygen around their body, a person can feel extremely tired.

5. Fast heart rate

A fast heart rate and shortness of breath may be symptoms of vitamin B-12 deficiency. A fast heart rate may be a symptom of vitamin B-12 deficiency.

The heart may start to beat faster to make up for the reduced number of red blood cells in the body. Anemia puts pressure on the heart to push a higher volume of blood around the body and to do it more quickly. This response is the body’s way of trying to ensure that enough oxygen circulates through all of the body’s systems and reaches all the organs.

6. Shortness of breath

Anemia that results from vitamin B-12 deficiency may cause a person to feel a little short of breath. It is possible to link this to a lack of red blood cells and a fast heartbeat.

Anyone who is experiencing real difficulty breathing should see a doctor straight away.

7. Mouth pain

Vitamin B-12 affects oral health. As a result, being deficient in vitamin B-12 may cause the following mouth problems:

  • glossitis, which causes a swollen, smooth, red tongue
  • mouth ulcers
  • a burning sensation in the mouth

These symptoms occur because vitamin B-12 deficiency causes a reduction in red blood cell production, which results in less oxygen reaching the tongue.

8. Problems thinking or reasoning

Vitamin B-12 deficiency may cause problems with thinking, which doctors refer to as cognitive impairment. These issues include difficulty thinking or reasoning and memory loss.

One study even linked low vitamin B-12 levels to an increased risk of Alzheimer’s disease, vascular dementia, and Parkinson’s disease.

The reduced amount of oxygen reaching the brain might be to blame for the thinking and reasoning problems.

9. Irritability

Being deficient in vitamin B-12 can affect a person’s mood, potentially causing irritability or depression.

There is a need for more research into the link between vitamin B-12 and mental health. One theory is that vitamin B-12 helps break down a brain chemical called homocysteine. Having too much homocysteine in the brain may cause mental health problems.

10. Nausea, vomiting, and diarrhea

Vitamin B-12 deficiency can affect the digestive tract.

A lack of red blood cells means that not enough oxygen reaches the gut. Insufficient oxygen here may lead to a person both feeling and being sick. It may also cause diarrhea.

11. Decreased appetite and weight loss

As a result of digestive problems, such as nausea, people with vitamin B-12 deficiency may lose their appetite. A decreased appetite can lead to weight loss in the long term.

12. dark circles under eyes

Vitamin B12 deficiency is one of the reasons of dark circles under eyes. [1]

What are the causes of vitamin B12 deficiency? 

  • Age-related factors that interfere with B12 absorption

One of the main factors associated with B12 deficiency, I am sorry to say, is age. Depending on the study population, between 5-20% of seniors have B12 deficiency.

Older individuals often have a combination of factors that interfere with B12 absorption. These include:

      • gastric atrophy (autoimmune or nonimmune)
      • achlorhydria (lack of stomach acid) due to proton pump inhibitors used to treat acid reflux
      • bacterial overgrowth in the intestines related to antibiotic use
      • excess alcohol consumption

Although these factors interfere with dietary B12 absorption, people with this type of B12 malabsorption, sometimes referred to as food cobalamin malabsorption, are able to absorb the form of B12 found in supplements.

  • Pernicious anemia

Pernicious anemia (PA) is an autoimmune disorder that interferes with B12 absorption. Individuals with the disorder develop autoantibodies that attack the acid-producing parietal cells of the stomach lining.

These cells also produce intrinsic factor. Other autoantibodies that target intrinsic factor (IF) are also present in many people with PA. Intrinsic factor is a protein binds to vitamin B12 to facilitate its absorption from the terminal ileum of the intestines into the bloodstream. Lack of IF leads to malabsorption of B2.

The result is that people with pernicious anemia have both achlorhydria (absence of stomach acid) and decreased absorption of dietary B12.

  • Dietary deficiency

Another cause of vitamin B12 deficiency is dietary. Vegans and vegetarians are, particularly, at risk. So are people who have inadequate animal-derived products in their diet. Additionally, some pregnant or lactating women who limit animal protein can become B12 deficient.

  • Other risk factors for B12 deficiency include:

      • Gastrectomy
      • Bariatric surgery
      • Gastritis
      • Pancreatic insufficiency
      • Small intestinal surgery or inflammation
      • H. pylori infection
      • Infestation with fish tapeworm
      • Chronic suppression of stomach acid (proton pump inhibitors, H2 receptor blockers, and antacids)
      • Long term use of metformin
      • Recreational use of nitrous oxide (laughing gas)
      • Genetic disorders

Treatment and prevention

Most people can get enough vitamin B-12 from dietary sources. For those who cannot, a doctor may prescribe or recommend B-12 supplements. People can also get B-12 supplements from drug stores or choose between brands online.

Most multivitamins contain vitamin B-12. People can take B-12 supplements in the form of oral tablets, sublingual tablets that dissolve under the tongue, or injections. A doctor can provide advice on the correct dosage of this vitamin.

People who have trouble absorbing vitamin B-12 may need shots of the vitamin to treat their deficiency.

A doctor can advise people on the best way to prevent vitamin B-12 deficiency, depending on their dietary choices and health.


The body needs vitamin B-12 for a range of bodily functions, which include making red blood cells. Being deficient in vitamin B-12 causes physical and psychological symptoms, including nerve problems, fatigue, and difficulty thinking.

Most vitamin B-12 deficiency symptoms occur due to a lack of red blood cells, which means that the body does not get enough oxygen. The body’s oxygen supply is crucial for many aspects of health.

As with other nutrients, the best way for most people to get vitamin B-12 is in the diet. If a person cannot get enough from their usual diet, fortified foods and other dietary supplements may help.

In most cases, doctors can treat vitamin B-12 deficiency. However, people with long-term deficiency may have long-lasting effects, such as nerve damage.

Spotting the signs of vitamin B-12 deficiency early on and getting the right treatment can improve a person’s outlook.

What is the recommended daily intake of vitamin B12?

The daily requirement for B12 is actually quite small – note that the amounts below are in micrograms. It also varies depending on the life stage as shown in the table below that was adapted from the National Institutes of Health Office of Dietary Supplements:

Life Stage Recommended Amount
Birth to 6 months 0.4 mcg
Infants 7–12 months 0.5 mcg
Children 1–3 years 0.9 mcg
Children 4–8 years 1.2 mcg
Children 9–13 years 1.8 mcg
Teens 14–18 years 2.4 mcg
Adults 2.4 mcg
Pregnant teens and women 2.6 mcg
Breastfeeding teens and women 2.8 mcg

The recommended average adult dietary intake is 2.4 micrograms a day in the U.S. (in the UK the recommended daily intake is only 1.5 mcg, and in the EU, it is 1.0 mcg).

Why so little? It’s because body stores of the vitamin (around 50% of which is in the liver) are relatively high at ~2-5 milligrams. That’s about 500,000 – 7,500,000 times the recommended dietary intake.

Because body stores are so large, it may up to 10 years of inadequate intake or malabsorption for the clinical manifestations fo B12 deficiency to develop.

Who should take supplements of vitamin B12?

From the discussion so far, it is obvious:

  • Vegans and vegetarians
  • People over 50 whose blood test documents a B12 deficiency
  • People who have pernicious anemia
  • People who have undergone some surgical gastric procedure, such as gastric stapling or resection.
  • People who chronically take proton pump inhibitors such as omeprazole (Prilosec) and lansoprazole (Prevacid), or H2 receptor antagonists such as cimetidine (Tagamet), famotidine (Pepcid), and ranitidine (Zantac).

Vitamin B12 is found in almost all multivitamins. Dietary supplements that contain only vitamin B12, or vitamin B12 with other nutrients such as folic acid and other B vitamins, are also available. Vitamin B12 is also available in sublingual forms (which are dissolved under the tongue), but there is no evidence that sublingual forms are better absorbed than pills. Vitamin B12 is also available as a prescription medication in a nasal gel form.

Which USANA products contains Vitamin B12 ?

vita-antioxidant contains Vitamin B-12
vita-antioxidant contains Vitamin B-12

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1 Comment

  1. Vitamin B12 Inhaler

    I might have liver surgery next month. Doc suggested that I improve the b12 levels before they operate. One of my friends asked me to take a vitamin B12 inhaler ( to fasten up the absorption process before the surgeries. Will that be safe? I’m unsure.

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