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Vitamin B12 is an important B vitamin. It is crucial for nerve tissue health, brain function, and the production of red blood cells. Cobalamin is another name for vitamin B12.

A deficiency or insufficiency can occur when levels of vitamin B12 become too low to meet the demands of the body. This can lead to a number of symptoms and can even progress to irreversible neurological issues if left untreated.

In the United States and United Kingdom, approximately 6% of adults aged 60 or younger have vitamin B12 deficiency. The rate jumps to 20% in people older than 60.

Vitamin B12 is a water-soluble vitamin, like all other B vitamins. This means it can dissolve in water and travel through the bloodstream. The body can store vitamin B12 for up to 4 years, and it can get rid of any excess or unwanted vitamin B12 in the urine.

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.

This article explores the functions of vitamin B12, how a person would know they are not consuming enough vitamin B12, and how to increase intake.

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Vitamin B12 is crucial to various bodily processes, including:

  • normal functioning of the brain and nervous system
  • cognitive functioning (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 normal red blood cell production (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 is characterized by impaired DNA synthesis and the formation of large, abnormal, immature red blood cells.

Intake requirements

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

Excessive intake of vitamin B12 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:

Vitamin B12 occurs naturally in many animal products. It does not typically occur 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:

  • older adults
  • those on restrictive diets like vegan diets
  • people with certain health conditions such as celiac disease

Learn more about vitamin B12 foods for vegetarians and vegans.

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.

hat said, even slightly lower-than-normal levels of vitamin B12 can trigger symptoms. However, these symptoms are nonspecific and are not enough to diagnose vitamin B12 deficiency. Symptoms may include:

  • depression
  • confusion
  • memory problems
  • fatigue
  • headaches
  • mood changes
  • difficulty concentrating

Once symptoms worsen, they can include neurological changes, such as numbness and tingling in the hands and feet. Some people may have difficulty maintaining balance.

Infants who lack vitamin B12 may show:

  • unusual movements, such as face tremors
  • reflex problems
  • feeding difficulties
  • irritation
  • eventual growth problems if left untreated

B12 deficiency has been linked to an increased risk of cognitive impairment and depression.

Insufficient vitamin B12 can also lead to anemia. The most common symptoms of anemia are fatigue, shortness of breath, and an irregular heartbeat. People with anemia might also experience:

  • a sore mouth or tongue
  • weight loss
  • pale or yellowing skin
  • diarrhea
  • menstrual problems

Who is at risk?

Several groups of people may be at an increased risk of vitamin B12 deficiency.

Vegans face a risk of vitamin B12 deficiency, as their diet excludes animal-sourced food products. Pregnancy and lactation can worsen deficiency in vegans. Unless a vegan diet is carefully planned, it is difficult to get enough vitamin B12 through plant foods alone. For this reason, it is recommended for those following vegan diets to supplement with B12.

Learn more about B12 foods for vegans and vegetarians here.

People with pernicious anemia may lack vitamin B12. Pernicious anemia is an autoimmune disease that affects the blood. Patients with this disorder do not have enough intrinsic factor (IF), a protein in the stomach that allows the body to absorb vitamin B12.

Other at-risk groups include people with small intestine problems, for example, an individual with a surgically shortened small intestine. Crohn’s disease is also a risk factor for vitamin B12 deficiency due to frequent involvement of the terminal ileum.

Gastritis, celiac disease, and inflammatory bowel disease (IBD) may lead to a deficiency because these conditions reduce nutrient absorption.

People with chronic alcohol use disorder may lack vitamin B12, as their bodies may not absorb nutrients efficiently.

People with diabetes who are treated with metformin should have their B12 levels tested by their healthcare professional regularly. This is because metformin reduces the absorption of vitamin B12.

Treatment for vitamin B12 deficiency includes oral vitamin B12 supplements or vitamin B12 injections.

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 breastfeeding.

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

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 2 weeks, or until the individual’s symptoms improve. Continuing treatment depends on if the cause of the deficiency relates to diet or if the individual has any accompanying neurological problems.

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

Hydroxocobalamin injections may cause side effects, including:

  • pain, swelling, or itching at the injection site
  • nausea or vomiting
  • headaches
  • dizziness
  • hot flashes

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

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

The body needs vitamin B12 for normal 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 can even lead to 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.