The benefits of vitamin B-12 include its support of the central nervous system, the skin, hair, liver and eyes, according to the University of Maryland Medical Center. However, high levels of vitamin B-12 can imbalance the other B vitamins, which should work in concert. Vitamin B-12 also can cause negative interactions with some medications or be harmful to people with certain diseases.
Vitamin B-12 also helps the body make DNA and RNA, says the University of Maryland Medical Center. B-12 also works with folic acid, also called vitamin B-9, to make red blood cells and help the body use iron more efficiently. The two vitamins also help the body make S-adenosylmethionine, a mood regulator. Along with vitamin B-6, folic acid and vitamin B-12 also regulate levels of homocysteine, high levels of which have been linked with heart disease.
People who take other medications, such as chemotherapy drugs, H2 blockers, some diabetes medications, proton pump inhibitors and anti-seizure medicines should consult with their doctors before taking vitamin B-12, advises the University of Maryland Medical Center. Those who suffer from Leber's disease shouldn't take vitamin B12, because it can damage the optic nerve.
Vitamin B-12 is found almost exclusively in animal products, leaving vegans and vegetarians at risk for vitamin B-12 deficiency, states the University of Maryland Medical Center. Older people and others who have low levels of the stomach acid needed to process vitamin B-12 may be at risk of deficiency.