Vitamin B12 is a large, complex member of the B complex of vitamins, which is necessary for numerous biochemical reactions in the body. Vitamin B12 is water soluble, which means that excess amounts that are ingested are usually flushed from the body in urine. Although vitamin B12 is typically safe and nontoxic, in certain situations, it may cause side effects. As with any health supplement, consult your doctor before you take vitamin B12.
Skin Irritation
One of the possible side effects of vitamin B12 is skin irritation. Vitamin B12 supplements have been reported to cause dry, itchy skin, sometimes leading to a rash or dermatitis. In very rare cases, vitamin B12 may cause a condition called rosacea fulminans, which is characterized by red, inflamed skin that may develop into boils and pustules.
Allergic Reaction
Certain individuals may experience an allergic reaction to vitamin B12 -- particularly to the metal cobalt ion that is part of the vitamin. If you are allergic to cobalt, use vitamin B12 with caution. Mild allergic reaction symptoms include headaches, nausea, dizziness, hives and a runny nose. In rare cases, severe reactions may occur causing swelling of the hands, face, lips, tongue and throat. Swelling of the throat can constrict the airways, leading to difficultly breathing. If you or someone you know experiences severe swelling of the face and difficulty breathing after taking vitamin B12, call a doctor immediately.
Additional Side Effects
Additional side effects may result from vitamin B12 supplements, including diarrhea. In some cases, vitamin 12 may increase the risk of blood clot formation, particularly in the arms and legs, which is a condition known as peripheral vascular thrombosis.
Disease Interactions
People with a rare hereditary eye disease called Leber's disease should not take vitamin B12. In people with Leber's disease, vitamin B12 can rapidly cause severe damage to the optic nerve, resulting in optic nerve atrophy and possibly vision loss. People who have an angioplasty procedure should also avoid vitamin B12, because the vitamin may cause complications with coronary stents.
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