Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. 

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Am Fam Physician. 2003;67(5):993-994

What is vitamin B12?

Vitamin B12 is an important vitamin that you usually get from your food. It is mainly found in meat and dairy products. Vitamin B12 helps make red blood cells and keeps your nervous system working right.

What happens if my vitamin B12 level is low?

If you have a very low vitamin B12 level, you might get anemia, depression, dementia, or a serious problem with your nervous system.

You might not have any symptoms if your vitamin B12 level is just a little bit low.

Some people with low vitamin B12 also have high levels of homocysteine (say this: homo-sis-teen), an amino acid in the blood. If you have both of these problems, you may have a higher risk of heart disease and stroke.

How does my doctor know I have a low vitamin B12 level?

Your doctor may check your blood to see if your vitamin B12 level is low. If your vitamin B12 level is close to low, and you have symptoms, your doctor may also check your blood to find out why your vitamin B12 level is low.

I eat meat and dairy products, so why do I have low vitamin B12?

Vegetarians who do not eat meat or dairy products are at risk for low vitamin B12, usually about two years after they become vegetarians. However, most people who have low vitamin B12 are not strict vegetarians. Most people with low vitamin B12 levels have trouble absorbing vitamin B12 from their stomach or small intestines.

What causes problems with absorbing vitamin B12?

Here are some reasons you might have trouble absorbing vitamin B12:

  • A disease called pernicious anemia (say this: per-nish-us ah-nee-mee-ah) could destroy the cells in your stomach that help you absorb vitamin B12.

  • If you use medicine for heartburn and ulcers for a long time, you may begin to have trouble absorbing vitamin B12.

  • If you have had surgery on your stomach or your intestines, you may have trouble absorbing vitamin B12.

Your doctor will be able to find out why you have a low vitamin B12 level by asking questions about your health, giving you a physical exam, and checking your blood, if necessary.

I have just been told I have a low vitamin B12 level. To raise it, can't I just take one multivitamin pill every day?

No. To raise your vitamin B12 level, you have to take at least 1,000 mcg of vitamin B12 every day. Over-the-counter multivitamins do not have this much vitamin B12. To get enough vitamin B12, you will need to take special vitamin B12 pills.

You can also get shots of vitamin B12. Usually, these shots are given every 1 to 2 days for about two weeks. After this, a shot is given once every month. Your doctor can help you decide what is the best treatment for you.

I have been getting a vitamin B12 shot every month for years. Can I change to a pill?

Possibly. In recent years we have found out that in most people, vitamin B12 pills work as well as shots. Ask your doctor if changing to pills would be OK for you.

How long do I have to take the pills or get the shots?

Most people with low vitamin B12 take the pills or get the shots for the rest of their lives.

Where can I get more information about vitamin B12 deficiency?

National Institutes of Health (Facts About Dietary Supplements)

American Heart Association (for information about homocysteine and heart disease)

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