Vitamin B12 Deficiency: Symptoms, Causes & Treatment

Home/Health Library/Diseases & Conditions/Vitamin B12 DeficiencyAdvertisementAdvertisementVitamin B12 DeficiencyMedically Reviewed.Last updated on 09/30/2025.

Vitamin B12 deficiency is a treatable condition that happens if you aren’t consuming enough vitamin B12 in your diet or if your body isn’t absorbing it properly. Vitamin B12 deficiency can cause physical, neurological and psychological symptoms. It can be treated with vitamin B12 medications.

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What Is Vitamin B12 Deficiency?

Vitamin B12 deficiency, sometimes called cobalamin deficiency, happens when your body is either not getting enough or not absorbing enough vitamin B12 from the foods you eat. Vitamin B12 is an important nutrient that helps your body make red blood cells and DNA, the genetic material in all of your cells. It’s essential to how your body functions. Without treatment, vitamin B12 deficiency can cause physical, neurological and psychological problems.

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What is vitamin B12?

Vitamin B12 is an important nutrient that helps your body keep your nerve cells and red blood cells healthy. It also helps your body make DNA.

Your body doesn’t make vitamin B12 on its own. You have to consume food and drinks that have vitamin B12 to get it. Vitamin B12 is found mostly in animal products, like fish, meat, dairy and eggs. It’s also in fortified foods (foods with vitamins and minerals added to them), like cereals, breads, plant-based milks and nutritional yeast.

Adults need around 2.4 micrograms (mcg) of vitamin B12 a day. And women who are pregnant or breastfeeding need more. The amount of B12 babies and children need varies based on age.

How does my body absorb vitamin B12?

Two things need to happen for your body to absorb vitamin B12 from the food you eat:

1. Hydrochloric acid in your stomach removes vitamin B12 from the food it is in.
2. Vitamin B12 combines with something called intrinsic factor, a protein your stomach makes.

Your digestive system can then absorb B12.

What is vitamin B12 deficiency anemia?

Vitamin B12 deficiency anemia happens when your body doesn’t have enough healthy red blood cells. As B12 helps make red blood cells, a lack of vitamin B12 can cause anemia. But you can also have a vitamin B12 deficiency without having anemia.

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Symptoms and Causes

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Symptoms of vitamin B12 deficiency

The symptoms of vitamin B12 deficiency can develop slowly and can get worse over time. You may have no symptoms despite having a low level of vitamin B12 in your body. Vitamin B12 deficiency can cause physical, neurological and psychological symptoms.

Physical symptoms can include:

• Feeling very tired or weak
• Experiencing nausea, vomiting or diarrhea
• Not feeling as hungry as usual
• Losing weight
• Having a sore mouth or tongue ulcers
• Having pale skin

Neurological symptoms can include:

• Numbness or tingling in your hands and feet
• Vision problems
• Having a hard time remembering things or getting confused easily
• Having a difficult time walking or speaking like you usually do

Psychological symptoms can include:

• Feeling depressed
• Feeling irritable
• Experiencing a change in the way you feel or behave

Vitamin B12 deficiency causes

Vitamin B12 deficiency happens if you aren’t eating enough vitamin B12 or your body isn’t absorbing the vitamin B12 you consume. Situations or conditions that can cause vitamin B12 deficiency include:

• Lack of vitamin B12 in your diet: People who don’t eat enough foods that have vitamin B12 or don’t eat foods fortified with B12 can develop a deficiency.
• Gastritis: Gastritis is inflammation of the stomach lining, and it’s a common cause of vitamin B12 deficiency. It can cause vitamin B12 deficiency due to a lack of hydrochloric acid in your stomach, which you need for B12 absorption.
• Pernicious anemia: People who have pernicious anemia don’t make intrinsic factor. You need intrinsic factor so your body can absorb B12 vitamin. People with pernicious anemia have a B12 vitamin deficiency.
• Digestive diseases: Diseases that affect your digestive system, like Crohn’s disease and celiac disease, can prevent your body from fully absorbing vitamin B12.
• Surgery: People who have had gastrointestinal surgery — like a gastric bypass — can have difficulty absorbing vitamin B12.
• Alcohol use disorder: This condition can damage your digestive system and cause vitamin B12 deficiency.
• MTFHR deficiency: A gene mutation (change) that makes it harder to metabolize B12 correctly. You need higher doses of vitamin B12 to function well and, sometimes, a special methylated B12 supplement.
• Transcobalamin II deficiency: This is a rare genetic disorder that makes it hard for vitamin B12 to circulate in your body.

Risk factors

You are more likely to develop vitamin B12 deficiency if you have one or more of the following risk factors:

• Being older than 75 years: People over 75 are more at risk for developing vitamin B12 deficiency because their bodies are often unable to fully absorb vitamin B12.
• Having a digestive system disorder: Digestive disorders can make it more difficult for your body to absorb vitamin B12.
• Following a vegan or vegetarian diet: Vitamin B12 is only naturally found in animal products, like meat and dairy. Because of this, people who eat a vegan or vegetarian diet are more likely to have a vitamin B12 deficiency if they aren’t taking a B12 supplement.
• Taking certain medications: Certain medications can cause low levels of vitamin B12 in your body, including metformin, proton pump inhibitors, H2 blockers and oral birth control pills.
• Having Sjögren’s syndrome: People with Sjögren’s syndrome are more likely to have vitamin B12 deficiency.
• Drinking excessive amounts of alcohol: Chronic alcohol use can damage your digestive system and cause vitamin B12 deficiency.

Complications of B12 deficiency

Left untreated, vitamin B12 deficiency can cause lasting side effects that affect your nervous system and brain. More severe side effects include:

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• Peripheral neuropathy
• Degeneration of your spinal cord
• Paralysis
• Bowel incontinence and/or urinary incontinence
• Erectile dysfunction
• Paranoia and delusions
• Memory loss

Diagnosis and Tests

How is vitamin B12 deficiency diagnosed?

It can be difficult to diagnose vitamin B12 deficiency because you may not have symptoms, or symptoms can be like other nutritional deficiencies. Healthcare providers will usually do blood tests to check for B12 deficiency in people who have a high risk of developing it.

Specific tests to help diagnose vitamin B12 deficiency are:

• Complete blood count (CBC)
• Vitamin B12 test
• Methylmalonic acid (MMA) test
• Homocysteine test

Management and Treatment

How is vitamin B12 deficiency treated?

Getting more vitamin B12 treats the deficiency. Providers may prescribe cyanocobalamin, a human-made form of B12. Options for vitamin B12 treatment include:

• Vitamin B12 oral medication
• Vitamin B12 injections
• Vitamin B12 nasal spray or nasal gel
• Eating more foods that are rich in B12 (like meat, fish, eggs and dairy)

Depending on the cause of the deficiency, you may only need treatment until your vitamin B12 levels are back to normal, or you may need B12 therapy for the rest of your life.

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Outlook / Prognosis

What can I expect if I have this condition?

What you can expect depends on how early the vitamin B12 deficiency is caught and how low your levels are. If your deficit is mild, you may respond quickly to medication and eating more foods containing B12.

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If you have chronic low B12 levels or have underlying health conditions that cause the deficiency, you may need to take B12 for the rest of your life (or for as long as you have the underlying condition).

Work with your healthcare provider to find the treatment that works best for you based on your situation.

Prevention

How can I prevent B12 deficiency?

Most people can prevent vitamin B12 deficiency by eating foods that have vitamin B12.

Options for consuming B12 include:

• Animal food products: Fish, milk, dairy products, eggs, poultry and red meat all contain vitamin B12.
• Fortified foods: Fortified foods are foods that have vitamins and nutrients added to them that they don’t naturally have. Fortified foods include certain breakfast cereals, nutritional yeast, plant milk and certain bread. You can check the food label to see if a food has been fortified with vitamin B12.
• Vitamin B12 dietary supplements: Many multivitamins have vitamin B12. There are also supplements that only contain vitamin B12. Ask your healthcare provider or pharmacist to help you choose which supplement is best for you.

Other things you can do to help prevent vitamin B12 deficiency include:

• Avoid alcohol: Frequent alcohol consumption can damage your digestive system and make it difficult for your body to absorb vitamin B12.
• Do your best to manage a digestive disease: If you have a digestive disease, be sure to follow your healthcare provider’s instructions to stay healthy.

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A note from Cleveland Clinic

Vitamin B12 is an important vitamin that your body needs to be healthy. But it’s one of those things that you probably don’t think about needing until you have symptoms of not having enough of it. Most of us can prevent vitamin B12 deficiency by consuming enough of it in the foods we eat. If you have risk factors for developing vitamin B12 deficiency or are experiencing symptoms, be sure to contact a healthcare provider to get a blood test to check your levels.

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Medically Reviewed.Last updated on 09/30/2025.

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References

Cleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards.

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Medically Reviewed.Last updated on 09/30/2025.

References

Cleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards.

• Ankar A, Kumar A. Vitamin B12 Deficiency (https://www.ncbi.nlm.nih.gov/books/NBK441923/). 2022 Oct 22. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Accessed 9/30/2025.
• Langan RC, Goodbred AJ. Vitamin B12 Deficiency: Recognition and Management (https://pubmed.ncbi.nlm.nih.gov/28925645/). Am Fam Physician. 2017 Sep 15;96(6):384-389. Accessed 9/30/2025.
• Merck Manual (U.S.). Vitamin B12 Deficiency (https://www.merckmanuals.com/home/disorders-of-nutrition/vitamins/vitamin-b12-deficiency). Last revised 8/2024. Accessed 9/30/2025.
• National Institutes of Health (U.S.). Vitamin B12 (https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/). Updated 12/2023. Accessed 9/30/2025.

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