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

Why do people take vitamin B-12?

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.

Since the evidence for treating elevated levels of homocysteine in the blood remains conflicting,  the current recommendation is screening of men over age 40 and women over age 50. For patients with elevated homocysteine levels, the recommendation is to supplement with folic acid and vitamin B-12. You should talk to your doctor before treating yourself for these conditions.

A recent 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.

How much vitamin B-12 should you take?

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

Category

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.

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