Vitamin B-12


What is vitamin B-12?

Vitamin B-12 is an important vitamin that you usually get from your food. It is mainly found in fish, shellfish, meat, eggs, dairy products and special fortified foods. Vitamin B-12 helps make red blood cells and DNA, and it keeps your nervous system working properly.

Most people with low vitamin B-12 levels either do not consume meat and dairy products or they have trouble absorbing vitamin B-12 from their stomach or small intestines. Vegetarians, vegans (strict vegetarians who do not eat any animal products) and the elderly are at higher risk for not getting enough vitamin B-12.

What can cause problems with absorbing vitamin B-12?

The following are some things that can cause problems with absorbing vitamin B-12:

  • Having a disease called pernicious anemia that destroys the cells in your stomach that help you absorb vitamin B-12.
  • Having an intestinal condition that interferes with the way your body absorbs food, such as Crohn's disease or celiac disease.
  • Having abnormal bacterial growth in your stomach.
  • Taking certain medicines that are used to treat heartburn, ulcers, and diabetes for a long time.
  • Having had surgery on your stomach or your intestines, such as gastric bypass surgery.

Your doctor will find out why you have a low vitamin B-12 level by asking questions about your health, giving you a physical exam and checking your blood. He or she may need to do other tests to check for a low level of vitamin B-12.

What happens if my vitamin B-12 level is low?

You might not have any symptoms if your vitamin B-12 level is just a little bit low. However, a very low vitamin B-12 level can cause symptoms of anemia, such as paleness, weakness and fatigue (severe tiredness). It can also cause depression, dementia and other serious problems with your nervous system. Damage to your nervous system that is caused by a low vitamin B-12 level can become permanent if you don't get treatment promptly.

Some people who have low vitamin B-12 levels also have high levels of homocysteine (say: "hoe-moe-sis-teen"), an amino acid (a building block of protein) in the blood. If you have low vitamin B-12 and high homocysteine, you may have a higher risk of heart disease and stroke.

Can I just take one multivitamin pill every day to raise a low vitamin B-12 level?

No. Over-the-counter multivitamins do not contain enough vitamin B-12 to raise a low level. To get enough vitamin B-12, you will need to take special vitamin B-12 pills.

You can also get shots of vitamin B-12. Usually, these shots are given every 1 to 2 days for about 2 weeks. After this, a shot is given once every month. Vitamin B-12 is also available as a prescription nose spray that is used either daily or weekly. This may be an option for patients who have used the shots to raise their vitamin B-12 level. Your doctor can help decide what form of vitamin B-12 is right for you.

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Vitamin B12 Deficiency by RC Oh, CPT, MC, USA and DL Brown, MAJ, MC, USA (American Family Physician March 01, 2003,

Written by editorial staff

Reviewed/Updated: 04/15
Created: 10/03