Vitamin B12: What Is It And Why Is It Important?

November 30, 2023
Foods high in vitamin B12

Vitamin B12 is a water-soluble vitamin that is found in meats and dairy products and is commonly taken as a supplement. Your body cannot make vitamin B12, so it must be consumed in your diet. Many people have difficulty absorbing vitamin B12. Once absorbed, vitamin B12 is stored in your liver in large amounts, so it takes several years to develop a deficiency.  

Vitamin B12 deficiency is common, affecting about 6% of people under the age of 60 and nearly 20% of people over the age of 60. A vitamin B12 deficiency may not be obvious, making it hard to diagnose. There is no definitive test to measure vitamin B12 levels either.1 Therefore, screening is not recommended unless you have a risk factor for vitamin B12 deficiency.2

What Does Vitamin B12 Do For Your Body?

Vitamin B12 is important for:

  • Growth
  • Cellular reproduction
  • Blood cell formation
  • Proper brain and nerve function
  • DNA formation
  • Protein synthesis
  • Carbohydrate metabolism
  • Controlling homocysteine levels
  • Stabilizing mood

What Food Has Vitamin B12?

Vitamin B12 is not found in plant products. Therefore, many foods are supplemented with vitamin B12. According to the National Institute of Health, foods that are high in vitamin B12 include:

  • Animal meat: especially clams, oysters, and beef liver
  • Fish
  • Eggs
  • Dairy
  • Fortified foods: breakfast cereals, nutritional yeast
A healthy diet for antiaging

What Happens When Your Vitamin B12 Is Low?

Vitamin B12 is essential for many chemical reactions in your body. Symptoms of vitamin B12 deficiency include:


  • Ringing in the ears
  • Tremors or involuntary muscle contractions
  • Numbness and tingling in the arms and legs
  • Confusion, memory problems
  • Muscle weakness
  • Unsteady gait
  • Difficulty with maintaining balance
  • Dizziness
  • A feeling that you need to move your legs at night
  • Vision, taste, or smell disturbances


  • Psychosis
  • Hallucinations
  • Depression
  • Mania
  • Anxiety
  • Irritability
  • Sleep disturbances


  • Insomnia
  • Weakened bones and fractures
  • Abnormal heart rhythms
  • Infertility
  • Weight loss
  • Stomach pain
  • Constipation
  • Appetite loss
  • Soreness of the mouth or tongue
  • Megaloblastic anemia leading to difficulty breathing, weakness, pale skin color, fatigue, and jaundice (yellow color to the skin or eyes)

If you have any of these symptoms or suspect that you have a vitamin B12 deficiency, supplementing with vitamin B12 can have many amazing benefits.

Vitamin B12: What Is It And Why Is It Important?

What Causes A Vitamin B12 Deficiency?

Vitamin B12 absorption is a complex problem. Inefficiencies or roadblocks in these steps can cause a vitamin B12 deficiency.

Step 1:

Specialized cells in the stomach, called parietal cells, produce hydrochloric acid and intrinsic factor.

Roadblock: Autoimmune disorders can destroy these important cells. This condition is called pernicious anemia and is an important cause of vitamin B12 deficiency.

Step 2:

Stomach acids and enzymatic proteins in the stomach break food down and separate vitamin B12 from other nutrients.

Roadblock: Taking antacids can raise the pH of your stomach contents. This makes it more difficult to separate vitamin B12 from foods. If you take antacids for indigestion or ulcers, you may be at an increased risk of vitamin B12 deficiency.

Older adults produce less stomach acid. This puts them at an increased risk for vitamin B12 deficiency. People who have had gastric bypass or other stomach surgeries are also at increased risk because parietal cells are removed when part of the stomach lining is removed.

Step 3:

The next step is binding to intrinsic factor. Intrinsic factor can only bind to approximately 56% of a 1 mcg dose of vitamin B12, and absorption decreases dramatically at doses over 1-2 mcg.

Roadblock: Consuming too high of an oral vitamin B12 dose means that much of it will be lost in the gastrointestinal tract.

Step 4:

After intrinsic factor binds to vitamin B12, the complex passes through the lining of the distal small intestine and enters the bloodstream.

Roadblock: If you have an inflammation of the bowel, it is hard for vitamin B12/intrinsic factor to pass through the bowel lining and into the bloodstream. Inflammatory bowel diseases are another important cause of vitamin B12 deficiency.

Increased Demand For Vitamin B12

Pregnancy and lactation increase the demand for vitamin B12 and can cause a deficiency.

Taking metformin for more than four months increases the risk of Vitamin B12 deficiency.

Vitamin B12: What Is It And Why Is It Important?

Inadequate Intake

People who consume a vegan or vegetarian diet are at an increased risk for vitamin B12 deficiency. Animal products and dairy are the primary dietary sources of vitamin B12. However, many foods are supplemented with vitamin B12.

People over age 75 frequently do not consume enough foods high in vitamin B12 in their diet.

Excessive alcohol consumption increases the risk of vitamin B12 deficiency.2

If you have a risk factor for vitamin B12 deficiency or have symptoms attributed to vitamin B12 deficiency, vitamin B12 supplements may be necessary to restore your levels. Vitamin B12 supplements are available in oral and injectable forms. Many people choose the injectable form because of the limits in absorbing oral vitamin B12.

Concerns Or Contraindications With Using Vitamin B12 Supplements

If you have any of the following, speak with a healthcare provider before supplementing with vitamin B12 in any form:

  • Eye problems or Leber’s disease
  • Kidney or liver disease
  • Iron or folic acid deficiency
  • An infection
  • Are receiving any medication or treatment that affects bone marrow

Vitamin B12 can also interact with some medications, including stomach acid inhibitors and metformin. Vitamin B12 injections have some side effects. In most cases, the benefits of vitamin B12 injections outweigh the risks.

Healthy diet

How Much B12 Should You Take A Day?

The recommended daily allowance for vitamin B12 varies by age and sex. These levels were set by the Institute of Medicine. The average adult consuming an omnivore diet gets about 3.4 mcg per day of vitamin B12 in their diet.

0-6 months0.4 mcg0.4 mcg
7–12 months0.5 mcg0.5 mcg
1–3 years0.9 mcg0.9 mcg
4–8 years1.2 mcg1.2 mcg
9–13 years1.8 mcg1.8 mcg
14+ years2.4 mcg2.4 mcg

Institute of Medicine (1998)

Approximately 24% of men and 29% of women take supplemental vitamin B12 and the injections are easy to self-administer. Looking to purchase and get a Vitamin B12 prescription? Shop Invigor Medical today!

Author: Leann Poston, M.D.
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  • Hunt A, Harrington D, Robinson S. Vitamin B<sub>12</sub> deficiency. BMJ : British Medical Journal. 2014;349:g5226. doi:10.1136/bmj.g5226
  • Langan RC, Goodbred AJ. Vitamin B12 Deficiency: Recognition and Management. Am Fam Physician. Sep 15 2017;96(6):384-389.
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