Risks of Too Much Vitamin B12

Vitamin B-12, also known as cobalamin and cyanocobalamin, is one of the eight B-complex vitamins. Vitamin B-12 is necessary for metabolism, DNA synthesis, production of red blood cells and maintenance of healthy nerve cells, according to FamilyDoctor.org. B-12 is naturally found in animal products such as meat, fish, milk and eggs. B-12 is also added to fortified foods such as breakfast cereals. Overdosing on vitamin B-12 can lead to several health problems. The recommended daily intake of B-12 is 2.4 micrograms for adults. There Institute of Medicine has not set a daily limit on B-12, according to Linus Pauling Institute, but you may begin experiencing symptoms if you ingest an amount that is too much for you.

Excess vitamin B-12 may cause the heart to stop pumping properly, leading to symptoms of heart failure, according to Drugs.com. Vitamin B-12 injections are more likely to cause immediate problems to the heart because the vitamins are administered directly into the bloodstream. Patients with heart problems should avoid taking over-the-counter vitamins without their doctor's approval.

Excess vitamin B-12 can damage liver and kidney cells, leading to symptoms of liver and kidney failure, according to Drugs.com. B-12 is metabolized in the liver and its by-products are removed from the body by the kidneys. Exposure of the liver to high levels of B-12 may cause damage to liver cells, leading to inflammation and scar formation. Kidney tubules may also be damaged by excess of B12 as it is excreted from the body. Patients with liver and kidney problems should consult their doctor before taking over-the-counter vitamins containing B-12.

Excess vitamin B-12 can lead to formation of blood clots in major blood vessels. Blood clots are dangerous because they prevent the flow of blood to body organs, which can cause organ failure, according to Drugs.com. Blood clots may also block blood vessels that transport blood to the heart and brain leading to heart attack and stroke. B-12 supplements should be used cautiously to prevent blood clots. Patients with previous histories of blood clots, stroke and heart attack should avoid taking vitamin B-12.