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What is vitamin B-12?

Vitamin B-12 is an important nutrient that is found naturally in some foods and added to others. It is also available as a dietary supplement. It is mainly found in fish, shellfish, meat, eggs, dairy products, and 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 eat or drink animal 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.

How much vitamin B-12 do I need?

The amount of vitamin B-12 your body needs depends on your age and whether you are pregnant or breastfeeding. The Food and Nutrition Board at the Institute of Medicine of the National Academies recommends the following daily intake of vitamin B-12 in micrograms (mcg).

Recommended Dietary Allowance (RDA) for Vitamin B-12
AgeRDA per day
0-6 months0.4 mcg
7-12 months0.5 mcg
1-3 years0.9 mcg
4-8 years1.2 mcg
9-13 years1.4 mcg
14-18 years2.4 mcg
19 years and older2.4 mcg

If you are pregnant, the recommended daily intake of vitamin B-12 is 2.6 mcg. If you are breastfeeding, the recommended daily intake of vitamin B-12 is 2.8 mcg.

What can cause trouble absorbing vitamin B-12?

The following can make it hard for you to absorb vitamin B-12 from your stomach or small intestines:

  • 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 (for example, Crohn’s disease or celiac disease)
  • Having abnormal bacterial growth in your stomach
  • Having certain immune system disorders (for example, Graves disease or lupus)
  • Drinking heavily
  • Having atrophic gastritis (irritation of the stomach lining), which decreases the acid in your stomach that helps you absorb vitamin B-12
  • 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 (for example, gastric bypass surgery)

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

A low level of vitamin B-12 in the body is referred to as a “vitamin B-12 deficiency.” If your vitamin B-12 level is just a little low, you might not have any symptoms. However, a very low vitamin B-12 level can cause symptoms such as:

  • Weakness
  • Fatigue (severe tiredness)
  • Pale skin
  • Fast heartbeat
  • Shortness of breath
  • Constipation or diarrhea
  • Loss of appetite
  • Gas
  • Depression
  • Dementia

If you have a very low vitamin B-12 level for a long time, it can damage your nervous system. This can cause symptoms such as numbness or tingling in your hands and feet. 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.

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 also need to do other tests.

Can I just take a 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. Most people can prevent vitamin B-12 deficiency by eating foods that are rich in B-12. However, if you don’t eat or drink animal products, or you have trouble absorbing vitamin B-12 from your stomach or small intestines, you may need to take special vitamin B-12 pills.

Prescription vitamin B-12 shots can be used to treat vitamin B-12 deficiency. 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 pill, nose spray, nasal gel, or an under the tongue medication. These may be options for patients who have used the shots to raise their vitamin B-12 level.

Your doctor can tell you if a vitamin B-12 supplement or medication will affect any medical conditions you have. He or she also needs to know about any prescription or over-the-counter (OTC) medicines, or other dietary supplements you are taking.



  • Update on Vitamin B12 Deficiency by Langan RC, Zawistoski KJ( 08/18/15)
  • National Institutes of Health, Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin B12. Accessed 08/10/15