What Is Vitamin B12?

An Essential Nutrient for Blood and Nervous System Function

An essential nutrient, cobalamin—better known as vitamin B12—benefits your body in many ways. These include helping your body produce energy, boosting memory and mood, making red blood cells and DNA, and improving your heart health.

Vitamin B12 is water-soluble, which means that your body can't store it in fat tissue. As a result, you need to get this vitamin through food. Sources of vitamin B12 include clams, beef, chicken, salmon, milk, eggs, and fortified nutritional yeast.

Foods that are good sources of vitamin B12
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What Does Vitamin B12 Do?

Vitamin B12 helps your body produce energy by converting carbohydrates into glucose.

Vitamin B12 also helps the nervous system function effectively. Working together with vitamin B9 (folate), it helps iron function better and helps the body to make healthy red blood cells. Together, folate and vitamin B12 work to produce S-adenosylmethionine (SAMe), a compound that assists with mood and immune function.

Hydrochloric acid in the stomach separates vitamin B12 from the protein in food. Vitamin B12 is then absorbed by the body and combined with a protein made by the stomach called intrinsic factor.

If a person can’t naturally make intrinsic factor, they have pernicious anemia. This means that they have difficulty absorbing vitamin B12 from dietary supplements and all foods.

Health Benefits of Vitamin B12

Vitamin B12 has many health benefits. It is known to help memory, mood, the nervous system, iron levels, heart health, hair, nails, and skin.

Blood Health

Vitamin B12 is an important factor in helping the body produce healthy red blood cells. When the body is deficient in or has low levels of vitamin B12, this can cause red blood cells to improperly develop.

As a result, the red blood cells become larger and irregular in shape. This prevents them from moving from the bone marrow to the bloodstream. (This is how megaloblastic anemia is caused.)

Anemia can cause weakness, fatigue, and other ailments over time, because your body doesn’t have enough red blood cells to give oxygen to your organs.

Brain Health

Studies show that vitamin B12 can help with brain and nervous system function, memory, mood, and depression.

Research has concluded that patients and people in the general population with depression have both low folate and low vitamin B12. Other studies have shown that vitamin B12 deficiency leads to poor memory. 

Skin Health

Vitamin B12 is known to help the skin, hair, and nails. Deficiency in the vitamin leads to discolored patches, skin hyperpigmentation, vitiligo, reduced hair growth, and more.

Heart Health

Studies show that vitamin B12 reduces homocysteine levels in the blood. Homocysteine is an amino acid that's connected with an increase in heart disease. Researchers have found that people who have modestly elevated homocysteine levels have higher rates of heart attack and stroke.

Vitamin B12 Food Sources

You can get vitamin B12 through supplements and foods. Foods that naturally have vitamin B12 include:

  • Lamb
  • Beef
  • Chicken breast
  • Clam
  • Salmon
  • Sardines
  • Trout
  • Tuna
  • Milk
  • Eggs
  • Ham
  • Plain Greek yogurt
  • Fortified nutritional yeast

Suggested Doses

The recommended dietary allowance of vitamin B12 is 2.4 micrograms per day. A normal range varies between 200 to 900 picograms per milliliter (pg/ml).

If a vitamin B12 value is less than 200 pg/ml, this is considered a vitamin B12 deficiency. A medical professional can administer a blood test to measure vitamin B12 levels.

Vitamin B12 Deficiency

A vitamin B12 deficiency can cause tiredness, weakness, numbness, and tingling in fingers and toes.

When vitamin B12 levels are low, the body cannot produce enough healthy red blood cells, leading to anemia. Red blood cells carry oxygen to parts of the body. Without enough cells delivering oxygen to your tissues and organs, the body will not function properly.


Symptoms of vitamin B12 deficiency include:

  • Irregular heartbeat
  • Weight loss
  • Tender tongue
  • Mood swings/Irritability
  • Anemia
  • Numbness or tingling in your hands and feet
  • Fatigue
  • Shortness of breath
  • Dizziness
  • Vitiligo
  • Pale or yellowish skin
  • Muscle weakness
  • Unsteady movements
  • Memory loss
  • Confusion

Who's at Risk of a Vitamin B12 Deficiency?

People who are likely to be deficient in vitamin B12 are older people who don’t produce enough hydrochloric acid in their stomach to absorb the vitamin naturally through food.

People who have digestive disorders such as Crohn's disease and celiac disease, as well as people who have had weight loss surgery or gastrointestinal surgery, may be deficient in B12 due to decreased absorption.

Other individuals include people who don’t consume many animal products. Vegetarians and vegans should ask their healthcare provider to check their vitamin B12 levels. Excessive alcohol consumption also puts people at risk of B12 deficiency.

Risks and Interactions

Although research has shown there is no risk in taking vitamin B12, it is important to contact your healthcare provider before you begin taking any vitamin, mineral, or supplement. A medical professional can best determine if it is a need for you at this time.

Research has shown that vitamin B12 can interact with some medications. According to the National Institute of Health, the following drugs are known to interfere with the body’s absorption of vitamin B12:

Before you take vitamin B12, talk to your practitioner or healthcare provider and tell them about any medications, vitamins, or supplements you are taking.

A Word From Verywell

Vitamin B12 is an essential nutrient in the human diet. It's critical for the development and normal functioning of many organs in the body. You should try to get your daily recommended intake of vitamin B12 from foods that naturally have vitamin B12.

If you are not sure you're getting enough vitamin B12 talk to your healthcare provider about getting a blood test, adding the proper foods to your diet, and possibly taking supplements.

Frequently Asked Questions

  • What are the signs of vitamin B12 deficiency?

    Vitamin B12 deficiency can cause anemia, balance problems, cognitive issues, difficulty walking, dizziness, fatigue, hair loss, irregular heartbeat, pale or yellow skin, shortness of breath, a sore or swollen tongue, and weakness. 

  • Does vitamin B12 make your hair grow?

    Vitamin B12 deficiency can cause hair loss. If your vitamin B12 levels are low, supplementing with B12 can improve your hair health.

    Other B-complex vitamins that support healthy hair growth include thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), and biotin (B7). 

  • Do B12 injections help you lose weight?

    Possibly, but probably not. There is a lack of solid evidence showing that vitamin B12 injections boost metabolism or promote weight loss.

    However, taking vitamin B12 may help boost your energy levels, especially in people with a B12 deficiency. Having more energy can help you be more active and burn more calories. Vitamin B12 deficiency can cause fatigue.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Office of Dietary Supplements. Vitamin B12.

  2. Johns Hopkins Medicine. Vitamin B12 deficiency anemia.

  3. Coppen A, Bolander-Gouaille C. Treatment of depression: time to consider folic acid and vitamin B12. J Psychopharmacol. 2005;19(1):59-65. doi:10.1177/0269881105048899

  4. Kannan R, Ng MJ. Cutaneous lesions and vitamin B12 deficiency: an often-forgotten linkCan Fam Physician; 54(4):529-532.

  5. Markišić M, Pavlović AM, Pavlović DM. The impact of homocysteine, vitamin B12, and vitamin D levels on functional outcome after first-ever ischaemic strokeBiomed Res Int. 2017;2017:5489057. doi:10.1155/2017/5489057

  6. Harvard Health. The A list of B12 foods.

  7. Harvard Health. Getting enough vitamin B12.

By Yvelette Stines
Yvelette Stines, MS, MEd, is an author, writer, and communications specialist specializing in health and wellness.