Vitamin B-12 (Cobalamin)

Medically Reviewed by Christine Mikstas, RD, LD on March 15, 2023
3 min read

Vitamin B-12 (cobalamin) plays a role in making DNA and also helps keep nerve cells and red blood cells healthy.

Vitamin B-12 has been looked at as a treatment for many diseases and conditions. These include fatigue, Alzheimer's disease, heart disease, breast cancer, high cholesterol, and sickle cell disease. However, the results have been inconclusive. Studies suggest that vitamin B-12 does not help with stroke risk or lung cancer.

Vitamin B-12 supplements do help people who have a deficiency. Low levels of vitamin B-12 are more likely in people over age 50. Vitamin B-12 is also more common in those with certain conditions, like digestive problems and some types of anemia. Low vitamin B-12 can cause fatigue, weakness, memory loss, and other problems with the nervous system.

There is some conflicting evidence about using vitamin B-12 to treat elevated levels of homocysteine in the blood. It is not fully understood how or if this elevation contributes to heart disease and other problems with blood vessels, or if the elevation is a result of these conditions. A high level of homocysteine in the blood is a risk factor for coronary, cerebral, and peripheral blood vessel disease. Risks also include blood clots, heart attacks, and certain types of stroke. However, recent guidelines do not recommend general screening for or treating elevated homocysteine levels unless there is suspicion of homocystinuria. That's a genetic condition that affects the body's ability to break down certain proteins. Instead of trying to treat yourself for elevated levels of homocysteine, it is important that you talk with your doctor about your concerns.

One study showed that vitamin B-12, used with folic acid and vitamin B6, reduces the risk for age-related macular degeneration (AMD) in women with heart disease or multiple risk factors for heart disease. Other research has linked vitamin B-12 with a reduced risk of developing AMD.

The recommended dietary allowance (RDA) includes the vitamin B-12 you get from both food and any supplements you take.


Vitamin B-12: Recommended Dietary Allowance (RDA) in micrograms (mcg)

For children under age 1, only an adequate intake (AI) is available

0-6 months

0.4 micrograms/day
Adequate Intake (AI)

7-12 months

0.5 mcg/day
Adequate Intake (AI)

1-3 years

0.9 mcg/day

4-8 years

1.2 mcg/day

9-13 years

1.8 mcg/day

14 years and up

2.4 mcg/day

Pregnant women

2.6 mcg/day

Breastfeeding women

2.8 mcg/day

Even at high doses, vitamin B-12 seems fairly safe. Experts have not found a specific dose of vitamin B-12 that's dangerous. No tolerable upper intake levels have been set.

Some good food sources of vitamin B-12 are:

  • Fish and shellfish
  • Meats
  • Poultry and eggs
  • Dairy products
  • Fortified cereals

Generally, it's best to get vitamins from whole foods. But doctors often suggest fortified foods -- and supplements -- to people over age 50. As we age, it's harder for our bodies to absorb vitamin B-12 from food.

  • Side effects and risks. Taken at normal doses, side effects are rare.  Allergies to vitamin B-12 supplements have been reported and can cause swelling, itchy skin, and shock.
  • Interactions. Drugs for acid reflux, diabetes, and other conditions may make it harder for your body to absorb vitamin B-12.