Vitamin B12 Side Effects

Updated June 13, 2017

Your body uses vitamin B12 to make DNA and maintain neurons and red blood cells. People take vitamin B12 supplements as a home remedy for conditions such as depression, immune system disorders, digestive problems and cancer, although, according to the Mayo Clinic, little evidence supports the vitamin's effectiveness for most of those conditions. Supplements of vitamin B12 greater than what the body needs may cause skin irritations and worsen certain types of nerve disorders.Ttaking in too little vitamin B12 can cause negative effects, as well.


Deficiencies of vitamin B12 may cause dementia, mood problems and psychosis, which you can reduce or improve by consuming the recommended daily allowance of 2.4mcg. of vitamin B12.

Pernicious Anemia

Pernicious anaemia is a hereditary disease caused by an inability of the body to absorb vitamin B12 from the blood. You can cure the disease by taking supplements of vitamin B12.

Sickle Cell

A combination of vitamin B12, folic acid and vitamin B6 has been found to reduce damage to the blood vessels caused by sickle cell disease, although, according to the Mayo Clinic, more studies are needed to confirm those results.


Pregnant women have a greater need for vitamin B12 to prevent loss of blood during pregnancy. You should consume 2.8mcg. per day during pregnancy or lactation.


Doses of vitamin B12 greater than 2.4mcg. per day can result in itching, rashes and rosacea, which may require treatment with steroids to resolve.


According to the Mayo Clinic, high doses of vitamin B12 can cause peripheral vascular thrombosis--blood clots that can result in swelling, pain and redness.

Leber's Disease

Taking vitamin B12 supplements can hasten the destruction of the optic nerve in Leber's disease.

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About the Author

Jessica Lietz has been writing about health-related topics since 2009. She has several years of experience in genetics research, survey design, analysis and epidemiology, working on both infectious and chronic diseases. Lietz holds a Master of Public Health in epidemiology from The Ohio State University.