A vitamin B12 deficiency can lead to a type of anemia called megaloblastic anemia. This can result in extra large red blood cells that can’t divide normally. You may be at risk if you have trouble absorbing nutrients.

Anemia is a condition that can develop if your levels of red blood cells are lower than normal. Anemia can be caused by many different factors, including a vitamin B12 deficiency.

Vitamin B12 is needed for the normal production of red blood cells. It also plays a role in maintaining healthy nerves. A B12 deficiency can lead to a type of anemia called megaloblastic anemia — a type of anemia where red blood cells are larger than normal and unable to divide properly. This can reduce the level of red blood cells in your body.

Your body can’t make its own vitamin B12, so you need to get it from food or supplements. Most cases of vitamin B12 deficiency are due to your body’s inability to absorb enough vitamin B12.

In the United States, around 6% of adults under 60 have a vitamin B12 deficiency. Older adults are more likely to have low B12 levels. It’s estimated that 20% of adults over the age of 60 are deficient.

This article will take a closer look at how a vitamin B12 deficiency can increase the risk of anemia and what you can do to treat or prevent low levels of B12.

Vitamin B12 is needed to make healthy red blood cells. To make red blood cells, a type of cell called a megaloblast is created first. The megaloblast needs vitamin B12 to be able to divide into smaller normal red blood cells.

Without B12, the megaloblasts can’t divide. They stay large and die earlier than healthy red blood cells. Some of these large red blood cells can’t get into the bloodstream. Their large size means that some get stuck in the bone marrow where they’re made.

All of these factors can cause the number of healthy red blood cells in your body to drop, which, in turn, can lead to anemia. This type of anemia is called megaloblastic anemia.

Megaloblasts also need folate to divide into healthy red blood cells. A folate deficiency can lead to megaloblastic anemia as well.

Anemia caused by a vitamin B12 deficiency can happen if you don’t have enough B12 in your diet or if you have trouble absorbing vitamins and nutrients. Once vitamin B12 levels are restored, your body will likely be able to make normal red blood cells again.

When levels of red blood cells drop, the symptoms of anemia are usually the same, no matter what the cause. Typical symptoms include:

Because vitamin B12 is needed for nerve health, a B12 deficiency can cause changes in nerve function. This may include:

  • changes in muscle movements
  • tingling sensation or pain, especially in your hands and feet
  • unexplained weight loss
  • changes in mood
  • memory issues
  • confusion
  • trouble walking
  • smell or taste changes

If you notice any of the above symptoms, contact a doctor. A simple blood test can provide more information about your vitamin B12 and red blood cell levels.

A vitamin B12 deficiency often develops from a lack of a protein called intrinsic factor. This protein is made in the lining of your stomach. It binds to B12 and allows this vitamin to get absorbed in the small intestine. If you don’t have enough intrinsic factor, you may have a harder time absorbing vitamin B12.

Low intrinsic factor, which can result in low levels of vitamin B12, may be caused by:

  • Pernicious anemia: Pernicious anemia is an autoimmune condition that destroys the cells that make intrinsic factor.
  • Gastric bypass surgery: Surgery that changes your stomach’s structure can reduce the amount of intrinsic factor available for B12 absorption.
  • Some medications: Some types of medications can change the conditions in your stomach and reduce the amount of intrinsic factor you create. Metformin, oral contraceptives, and proton pump inhibitors are just a few examples.
  • Infection with Helicobacter pylori: H. pylori, a bacteria that can infect your stomach, may affect your ability to make intrinsic factor.
  • Being older: People older than 50 are more likely to experience changes to their stomach acid, which could affect their ability to absorb vitamin B12.

Additionally, digestive conditions such as inflammatory bowel disease (IBD), celiac disease, or Crohn’s disease may also result in a B12 deficiency due to a lack of absorption in the small intestine.

It can take time to develop a deficiency, since your body can store enough vitamin B12 to last 2 to 4 years. Ongoing monitoring through blood work is important for anyone at risk.

If your doctor suspects you might have a vitamin B12 deficiency, they’ll order blood tests to measure your levels of B12. These tests will provide more details about your vitamin B12 levels and the health of your red blood cells.

Oral B12 supplements may be the first approach to treat a deficiency. The supplements can be swallowed or dissolved under your tongue.

If supplements don’t work to raise B12 levels, vitamin B12 can be injected. When injected, B12 doesn’t require intrinsic factor for it to be absorbed.

The amount of vitamin B12 your body needs is actually quite low. Unless you don’t eat animal products, you’ll likely be able to get enough B12 from your diet.

Adults only need 2.4 micrograms (mcg) of vitamin B12 daily. If you eat a balanced diet, you’ll likely be able to get enough B12 from your diet. While vitamin B12 is primarily found in animal products, there are a few plant-based sources as well.

Good food sources of vitamin B12 include:

  • fish and shellfish
  • dairy products
  • meat
  • poultry
  • eggs
  • nutritional yeast
  • foods with added B12, such as breakfast cereals

In many cases, a vitamin B12 deficiency is more likely to be caused by not being able to absorb enough B12 than by having a diet that’s deficient in this vitamin.

A vitamin B12 supplement may be recommended to prevent a deficiency if you:

  • don’t consume any animal products
  • take medications that affect your body’s ability to absorb B12, including proton pump inhibitors or metformin
  • have had gastric bypass surgery or have another digestive condition that affect your body’s ability to absorb nutrients

A vitamin B12 deficiency can cause a type of anemia called megaloblastic anemia. This is when red blood cells are too large and can’t divide like healthy red blood cells. This can result in a lower level of red blood cells.

Most people get enough vitamin B12 through the foods they eat, but several factors can affect the ability to absorb B12 properly. Medications, health conditions, and age can all affect levels of intrinsic factor, which is needed to help with absorption.

Treatment for megaloblastic anemia includes oral B12 supplements or B12 injections. For anyone at risk of vitamin B12 deficiency, regular blood work can monitor for changes in red blood cells and B12 levels.