Vitamin B12 (cobalamin) is essential for the health of nerve tissue, brain function, and red blood cells. Sources include meat, eggs, and some yeast products.

Vitamin B12 is the largest and most structurally complicated vitamin. It occurs naturally in animal products like meat and eggs, and manufacturers can produce it through bacterial fermentation synthesis.

People with a B12 deficiency may need supplements. Signs of a deficiency include headaches and fatigue. A deficiency or insufficiency can occur when levels of vitamin B12 become too low to meet the demands of the body.

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Like all other B vitamins, vitamin B12 is water-soluble. This means it can dissolve in water and travel through the bloodstream. The body can store vitamin B12 for 2 to 5 years, and it can get rid of any excess or unwanted vitamin B12 in the urine.

The main purpose of vitamin B12 involves:

  • keeping the body’s nerve and blood cells healthy
  • helping create DNA
  • preventing anemia, which is a low amount of red blood cells, resulting in less oxygen in the body

Vitamin B12 is crucial to various bodily processes, including:

  • normal functioning of the brain and nervous system
  • cognitive functioning or the ability to think
  • formation of red blood cells and anemia prevention
  • helping create and regulate DNA
  • possibly preventing congenital abnormalities
  • helping protect the eyes from macular degeneration
  • necessary for energy production

Vitamin B12 is essential for healthy blood. When the body does not have enough B12, it leads to decreased typical red blood cell production or anemia, which impairs oxygen delivery.

Megaloblastic anemia, also called nutritional-deficiency anemia, is a type of anemia caused by B12 or folate deficiency. Megaloblastic anemia has impaired DNA synthesis and the formation of large, abnormal, immature red blood cells.

Intake requirements

The National Institutes of Health (NIH) recommends that teens and adults over the age of 14 consume 2.4 micrograms (mcg) of vitamin B12 daily, pregnant people 2.6 mcg, and lactating people 2.8 mcg.

Excessive vitamin B12 intake has not shown toxic or harmful qualities. However, people should speak with their physician before starting any new supplements.

Some medications may decrease the absorption of vitamin B12 from foods. These medications include:

Doctors do not consider vitamin B12 as toxic in high quantities.

Hydroxocobalamin injections, or manufactured B12 injections, may cause side effects, including:

Serious side effects are rare. However, if people experience palpitations or signs of allergic shock after an injection, they should contact their doctor immediately.

Having low or deficient B12 levels can lead to a number of symptoms, some of which can be serious. It can result in irreversible and potentially severe damage, especially to the nervous system and brain. This, however, is uncommon.

Vitamin B12 is naturally present in many animal products. It is not typically present in plant foods unless it is supplemented.

Good dietary sources of vitamin B12 include:

  • beef
  • pork
  • ham
  • poultry
  • lamb
  • fish, especially haddock and tuna
  • dairy products, such as milk, cheese, and yogurt
  • some nutritional yeast products
  • eggs

Additionally, manufacturers fortify some types of plant milk and breakfast cereals with vitamin B12.

Even though vitamin B12 is found in a variety of foods, some people are at an increased risk of developing B12 deficiency or insufficiency. Groups at an increased risk include:

Some people have difficulties absorbing vitamin B12 from food sources and may need to take supplements.

Some populations may have problems absorbing vitamin B12 from food, including:

  • older adults
  • people with pernicious anemia
  • those with intestinal disorders

People can take B12 supplements orally or in a nasal spray. However, oral supplements may not help in many cases of deficiency. In these circumstances, a doctor may recommend vitamin B12 injections.

Vegans and others who do not get enough B12 from their diet can take supplements to avoid deficiency. This is particularly important during pregnancy and while nursing.

People can purchase various B12 supplements in health food stores and online. However, supplements are not FDA regulated and people should be careful when taking them, and ensure they purchase them from a reliable source.

Injection

Doctors may prescribe vitamin B12 injections for some individuals with pernicious anemia, or issues with vitamin B12 malabsorption and severe deficiency.

These injections consist of vitamin B12 in cyanocobalamin or hydroxocobalamin forms.

A healthcare professional typically administers these injections into a muscle every other day for two weeks or until the individual’s symptoms improve. Continuing treatment depends on whether the cause of the deficiency is diet or neurological.

Foods highest in B12 include:

  • meats such as beef, pork, and ham
  • dairy products such as cheese and milk
  • eggs
  • poultry

The fastest way to fix B12 deficiency would be to eat foods high in vitamin B12, such as beef, chicken, or dairy products, or take a B12 supplement.

Vitamin B12 is an essential vitamin mainly found in animal products. Most adults require 2.4 mcg daily.

The body needs vitamin B12 for typical function of the brain and nervous system, the formation of red blood cells, and other critical processes.

Deficiencies in vitamin B12 can lead to symptoms like headaches, fatigue, and digestive problems, and they can even cause nerve damage and cognitive issues.

Some people are more at risk of deficiencies, such as older adults and those who do not absorb nutrients well. Vegans may also have a deficiency risk, as their diet excludes many B12 sources.

Most people who eat a balanced diet receive enough B12. For others, doctors may recommend oral supplements or injections.