Vitamin B12 deficiency anemia is a type of megaloblastic anemia, the other type is folate deficiency anemia. All vitamins are essential for the body and their deficiency can cause health problems. In this post, we discuss vitamin B12 deficiency.

Vitamin B12 is needed to produce fully functional red blood cells in the bone marrow, and it is the red blood cells that carry oxygen to all parts of your body.

In vitamin B12 and folate deficiency, your blood picture isn’t healthy. This deficiency causes the body to produce abnormally large red blood cells that are not healthy and do not function well.

Due to a lack of red blood cells, your tissues and organs don’t get enough oxygen, as a result of which the various tissues and organs do not function well and you develop health issues.

Causes of vitamin B12 deficiency

Aging is often the cause of B12 deficiency. This is because as you grow older, your stomach produces less acid, which makes it harder to absorb vitamin B12 from the food. Therefore, even with a good diet older people can become B12 deficient.

In the United States and the United Kingdom, about 6% of adults younger than 60 years have a vitamin B12 deficiency, but the figure rises to 20% in those older than 60 years.

Other causes of B12 deficiency include

  • Taking antacids and acid-blockers for heartburn to suppress stomach acid
  • Eating a diet that does not contain vitamin B12 such as animal foods
  • Weight loss surgery
  • Autoimmune diseases that attack the gastrointestinal tract such as Crohn’s disease and celiac disease
  • Pernicious anemia occurs when the body’s immune system attacks cells in the stomach that produce a substance called intrinsic factor, without which B-12 can’t be absorbed in the intestines. If you have B12 deficiency caused by pernicious anemia, your risk of developing stomach cancer is high.

Who is at risk of developing Vitamin B12 deficiency?

The following groups are among those most likely to become vitamin B12 deficient.

  • Older adults. The reason why older people suffer from B12 deficiency is due to the associated presence of chronic atrophic gastritis. Conditions associated with B12 deficiency include pernicious anemia and Helicobacter pylori infection. Atrophic gastritis is an autoimmune disorder, which decreases the production of intrinsic factor and secretion of hydrochloric acid in the stomach that results in decreased absorption of vitamin B12
  • Individuals with pernicious anemia. Pernicious anemia is an irreversible autoimmune disease that affects the gastric mucosa and causes the gastric mucosa to atrophy. This is called gastric atrophy. This causes decreased production of intrinsic factor and resulting poor absorption of vitamin B12. Therefore, pernicious anemia causes vitamin B12 deficiency, even with proper intake of vitamin B12.
  • Individuals with gastrointestinal disorders. Individuals with small intestine disorders, such as celiac disease and Crohn’s disease, cannot absorb enough off vitamin B12 from food and therefore develop B12 deficiency.
  • Those who have had gastrointestinal surgery. Individuals who undergo bariatric surgery for weight loss are prone to B12 deficiency. Bariatric surgery can cause the removal of cells that secrete hydrochloric acid and cells that secrete intrinsic factor. Since they are responsible for B12 absorption, their removal leads to its deficiency
  • Vegetarians. Vegetarians and vegans who do not consume foods of animal origin such as poultry, meats, fish, and eggs are at a higher risk of developing vitamin B12 deficiency because plant-based foods lack vitamin B12. However, they can reduce their risk by consuming foods fortified with vitamin B12 (such as fortified nutritional yeast). If that’s not enough, they can take vitamin B12 supplements, which can negate the risk.
  • Infants of vegan women. Exclusively breastfed infants of women who do not consume animal food products might have very limited reserves of vitamin B12 and can develop vitamin B12 deficiency. Since the mother is deficient, the infant does not get the appropriate supply through breast milk and becomes deficient. The deficiency in such infants can be severe, especially if the mother has a severe deficiency or suffers from pernicious anemia. Sometimes, the deficiency remains undetected and remains untreated. Such infants can suffer neurological damage, failure and delay in the development of milestones, and anemia.

In such patients who are at risk of developing B12 deficiency, routine monitoring of B12 should be performed.

Treatment should be started only if they turn deficient. Prophylactic treatment before B12 levels fall is contraindicated.

Symptoms of full-blown B12 deficiency include:

Vitamin B12 deficiency anemia usually develops gradually over months or years. Signs and symptoms may be mild so as to go undetected at first but worsen as the deficiency becomes more severe.

Symptoms may include:

  • Balancing problems
  • Depression
  • Extreme fatigue or muscle weakness
  • Shortness of breath
  • Dizziness
  • Pale skin
  • Memory loss or confusion
  • Numbness or tingling in the hands and legs
  • Anemia
  • Irregular heartbeats
  • Mouth ulcers


In patients with suspected B12 deficiency, your doctor will order initial lab tests, which will include a complete blood count (CBC) and tests to determine serum B12 and folate levels.

In B12 deficient patients, the CBC would show anemia, which presents as decreased levels in both hemoglobin and hematocrit.

Additionally, the mean corpuscular volume (MCV) will be increased beyond 100 (normal values are 80 to 100 fl).

Your doctor will order tests to determine serum B12 and folate levels. He will do this because folic acid deficiency also presents as macrocytic anemia and is often confused with B12 deficiency.

Ordering serum levels of both B12 and folate can help remove any confusion.

  • A serum B12 above 300 pg/mL is interpreted as normal.
  • Levels between 200 and 300 pg/mL are considered borderline.
  • B12 levels below 200 pg/mL are considered deficient.

After a B12 deficiency confirmation, the etiology must be addressed. History taking and further investigations are done to rule out an improper diet, bariatric surgery, resection of terminal ileum where B12 is most absorbed, lack of intrinsic factor due to Crohn’s disease or celiac disease.

Treatment of B12 deficiency

Treatment of vitamin B12 deficiency involves repletion of the deficiency with B12 supplements.

In patients who are deficient due to a strict vegan B12 deficient diet, an oral supplement of B12 is usually enough to replete the depleted reserves.

Patients with a deficiency in intrinsic factor, either due to pernicious anemia or Crohn’s disease, can be treated with 1000 mcg intramuscular cobalamin injection once a month, since oral B12 will not be fully absorbed.

In patients who have undergone Roux-en-Y gastric bypass surgery and have subsequently become B12 deficient, supplementation with high doses (1,000 mcg/day) of oral methylcobalamin supplements or with hydroxocobalamin injections is indicated.

In newly diagnosed patients, 1000 mcg of intramuscular B12 is given once a week for four weeks. Once the depleted stores are replenished, your doctor will switch you to once a monthly injection.

Oral B12 is also effective in individuals lacking the intrinsic factor at high doses that will fully saturate intestinal B12 receptors.

Once you begin treatment, it can take up to six to 12 months to fully recover from B12 deficiency. You may also not experience any improvement during the first few months of treatment.

B12 Supplements: Tablets and injections

Vitamin B12 that is added to fortified foods and dietary supplements is already in free form and therefore is easily absorbed in the body.

Additionally, the bioavailability of B12 from dietary supplements is about 50% higher than that from food sources, which makes it more easily available for absorption.

Vitamin B12 supplements are present in various combinations:

  • As multivitamins with minerals. Multivitamin/mineral supplements typically contain vitamin B12 at doses ranging from 5 to 25 mcg
  • With other B-complex vitamins. In such supplements, vitamin B12 levels are higher, generally 50–500 mcg
  • As vitamin B12 alone. Such supplements contain even higher doses, typically 500–1,000 mcg

B12 supplements come containing all forms of vitamin B12 but cyanocobalamin supplements are the most common. Adenosylcobalamin, methylcobalamin, and hydroxocobalamin supplements are less common.

The absorption rates of vitamin B12 in supplements remain the same in all forms of vitamin B12.

In addition to oral supplements, vitamin B12 is available in sublingual preparations such as tablets or lozenges. Both these preparations are equally effective.

Cyanocobalamin and hydroxocobalamin forms of vitamin B12 can be administered as intramuscular injections and are available on prescription. These parenteral supplements can also be administered intravenously though they are more frequently used intramuscularly.

Parenteral administration is typically used to treat severe vitamin B12 deficiency caused by pernicious anemia, tropical sprue, and pancreatic insufficiency. These conditions do not allow the absorption of B12 and can lead to severe vitamin B12 deficiency.

Vitamin B12 is also available as a prescription nasal gel spray, which is effective in raising vitamin B12 blood levels in adults and children. The bioavailability of B12 with intranasal administration is similar to the bioavailability of an oral dose.