The National Institutes of Health (NIH) states that vitamin B12 is necessary for the metabolism, proper functioning of the nervous system and for the production of red blood cells. The body does not store excess vitamin B12, so it needs to be replaced daily. Although it is available in limited food sources such as meat and dairy, B12 intake from supplements or from a prescription for anemia or sufferers from a B12 deficiency are also sources. Vitamin B12 usually presents no side effects, but some have been noted.
Skin Side Effects
The initial and most obvious side effect of vitamin B12 is a skin reaction such as hives, flushing, rash, swelling and itchiness. The US National Library of Medicine indicates that rosacea is also reported in association with B12 use, and that symptoms can remain for up to 4 months after the vitamin has been discontinued. The Mayo Clinic advises that, while these reactions can occur, they also subside as the body adjusts to the vitamin intake.
Intestinal Side Effects
The US National Library of Medicine also reports diarrhea or loose stools due to vitamin B12 use. When vitamin B12 is taken as the synthetic cyanocobalamin, often used in supplementation or medical application, diarrhea can be accompanied by nausea, vomiting and indigestion. Glossitis, which is swelling of the tongue, can also occur.
Lung and Heart Side Effects
Side effects that involve the lungs and heart are difficulty breathing accompanied by a tightness in the throat. Chest pain is also reported, and the US National Library warns that patients with stenting---a mesh tube that is used to prop open an artery or blood vessel---can experience a renarrowing of the blood vessel.
Nervous System and Pain Side Effects
Nervous system side effects include headache, anxiety, nervousness, dizziness and a decrease in the sense of touch, known as hypoestesia. These effects are linked to the use of cyanocobalamin, the synthetic form of vitamin B12. Pain, specifically back pain, is also a side effect. Less reported side effects are the inability to walk normally and a lack of coordination.
If you are taking vitamin B12, be sure to report any adverse reactions to your physician. If you are currently on any medication, or have any heart condition, speak to your doctor before beginning any B12 intake.
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