Health Encyclopedia

Vitamin B12

Definition

Vitamin B12 is a water-soluble vitamin. Water-soluble vitamins dissolve in water. After the body uses these vitamins, leftover amounts leave the body through the urine.

The body can store vitamin B12 for years in the liver.

Alternative Names

Cobalamin; Cyanocobalamin

Function

Vitamin B12, like the other B vitamins, is important for protein metabolism. It helps in the formation of red blood cells and in the maintenance of the nervous system.

Food Sources

Vitamin B12 is naturally found in animal foods such as fish, meat, poultry, eggs, milk, and milk products. Vitamin B12 is generally not present in plant foods. Fortified breakfast cereals are a readily available source of vitamin B12. The vitamin is more available to the body from these cereals for vegetarians. Some nutritional yeast products also contain vitamin B12.

You can get the recommended amounts of vitamin B12 by eating a variety of the foods including:

Organ meats (beef liver)
Shellfish (clams)
Meat, poultry, eggs, milk and other dairy foods
Some fortified breakfast cereals and nutritional yeasts

To find out if vitamin B12 has been added to a food product, check the nutrition fact panel on the food label.

The body absorbs vitamin B12 from animal sources much better than plant sources. Non-animal sources of vitamin B12 have different amounts of B12. They are not thought to be good sources of the vitamin.

Side Effects

Vitamin B12 deficiency occurs when the body does not get or is not able to absorb the amount of the vitamin that the body needs.

Deficiency is most common in people who:

Are over the age of 50
Follow vegetarian or vegan diet
Have had stomach or intestinal surgery, such as weight loss surgery
Have digestive system conditions such as celiac disease or Crohn disease

Talk to your health care provider about taking vitamin B12 supplements.

Low levels of B12 can cause:

Anemia
Dementia
Loss of balance
Numbness or tingling in the arms and legs
Weakness

Recommendations

Recommendations for vitamin B12, as well as other nutrients, are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board at the National Academies of Sciences, Engineering, and Medicine. DRI is a term for a set of reference intakes that are used to plan and assess the nutrient intakes of healthy people. These values, which vary by age and sex, include:

Recommended Dietary Allowance (RDA): The average daily level of intake that is enough to meet the nutrient needs of nearly all (97% to 98%) healthy people. An RDA is an intake level based on scientific research evidence.

Adequate Intake (AI): This level is established when there is not enough scientific research evidence to develop an RDA. It is set at a level that is thought to ensure enough nutrition.

Dietary reference intakes for vitamin B12:

Infants (AI)

0 to 6 months: 0.4 micrograms per day (mcg/day)
7 to 12 months: 0.5 mcg/day

Children (RDA)

1 to 3 years: 0.9 mcg/day
4 to 8 years: 1.2 mcg/day
9 to 13 years: 1.8 mcg/day

Adolescents and Adults (RDA)

Males and females age 14 and older: 2.4 mcg/day
Pregnant teens and women: 2.6 mcg/day
Breastfeeding teens and women: 2.8 mcg/day

The best way to meet your body's vitamin B12 needs is to eat a wide variety of animal products.

Supplemental vitamin B12 can be found in the following:

Almost all multivitamins. Vitamin B12 is better absorbed by the body when it is taken along with other B vitamins, such as niacin, riboflavin, and vitamin B6, along with magnesium.
A prescription form of vitamin B12 can be given by injection or as a nasal gel.
Vitamin B12 is also available in a form that dissolves under the tongue (sublingual).

References

Litwack G. Vitamins and nutrition. In: Litwack G, ed. Human Biochemistry. 2nd ed. Philadelphia, PA: Elsevier; 2022:chap 20.

Mason JB, Booth SL. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 205.

Markell M, Siddiqi HA. Vitamins and trace elements. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 27.

National Institutes of Health website. Vitamin B12: fact sheet for health professionals. ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Updated December 22, 2022. Accessed February 21, 2023.

Review Date:1/19/2023
Reviewed By:Stefania Manetti, RD/N, CDCES, RYT200, My Vita Sana LLC - Nourish and heal through food, San Jose, CA. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997-A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

The Agency for Health Care Administration (Agency) and this website do not claim the information on, or referred to by, this site is error free. This site may include links to websites of other government agencies or private groups. Our Agency and this website do not control such sites and are not responsible for their content. Reference to or links to any other group, product, service, or information does not mean our Agency or this website approves of that group, product, service, or information.

Additionally, while health information provided through this website may be a valuable resource for the public, it is not designed to offer medical advice. Talk with your doctor about medical care questions you may have.