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Toxic Levels of Vitamin B12 (Methylcobalamin)

Aug 18, 2011 | By Sarka-Jonae Miller

Two forms of vitamin B-12 are in your body, methylcobalamin and 5-deoxyadenosyl cobalamin. Supplements use a form of vitamin B-12 called cyanocobalamin that the body converts into methylcobalamin and 5-deoxyadenosyl. Vitamin B-12 has a low potential for toxicity, but high amounts of vitamin B-12 may increase the risk of developing prostate cancer. It can also cause harmful side effects in some people.

Prostate Cancer

A study conducted at the Department of Medical Biosciences, Clinical Chemistry and the Umea University Hospital in Umea, Sweden researched the effects of taking vitamin B-12, folate and homocysteine on 254 case subjects with prostrate cancer and 514 matched control subjects. The researchers previously thought that the supplements may have a protective effect on prostate cancer, but instead the researchers found a three-fold increase in risk in patients taking vitamin B-12. The study was published in the "International Journal of Cancer" in February 2005.

Side Effects

Some people experience allergic reactions to vitamin B-12 supplements or are sensitive to cobalamin or cobalt, Mayo Clinic reports. Vitamin B-12 is also contraindicated if you have certain conditions. For example, people with the hereditary optic nerve atrophy disease known as Leber's disease should not take vitamin B-12 because it might cause severe and swift optic atrophy. Optic atrophy is the deterioration of the optic nerve, which carries nerve impulses from the eyes to the brain. Other possible side effects include rashes, itching and diarrhea, but you should speak with your doctor if you think you are experiencing reactions to vitamin B-12.

Recommended Amounts

Generally, the recommended supplemental dose for vitamin B-12 is between 1 mcg to 25 mcg daily, according to MedlinePlus. More specific recommendations are age dependent. The recommended dietary allowances for infants up to 6 months old should take 0.4 mcg. Infants 7 to 12 months old require 0.5 mcg. Children from 1 to 3 years of age, between 4 and 8 years and 9 to 13 years need 0.9 mcg, 1.2 mcg and 1.8 mcg respectively. Children over 14 and adults should get 2.4 mcg. Pregnant women need an additional 2 mcg for a total of 2.6 mcg. Women who are nursing should consume 2.8 mcg.

Deficiency

Although vitamin B-12 toxicity doesn't seem to be a real threat, vitamin B-12 deficiency is a concern. Your body stores several years' worth of vitamin B-12 and since the amounts needed aren't very high, deficiencies are rare. Even 1 cup of milk with a cup of raisin bran can provide enough vitamin B-12 for a day. Seniors, strict vegetarians and vegans may be at risk from not eating enough vitamin B-12. It's also possible to lack vitamin B-12 because your body cannot absorb it. A disease known as pernicious anemia is known to interfere with the absorption of vitamin B-12. Liver disorders, certain medications and enzyme deficiencies are other possible causes of a vitamin B-12 deficiency. Your doctor can check your vitamin B-12 levels to make sure you are getting enough.

References

Article reviewed by Avraham Zuroff Last updated on: Aug 18, 2011

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