The Harmful Effects Of Too Much Vitamin B12

The human body needs vitamin B-12 to synthesize new cells and maintain the normal functions of nerve cells. Since vitamin B-12 dissolves in water, it makes it difficult for the body to store vitamin B-12, thus people need to constantly obtain this vitamin through dietary intake. Research studies have not shown much evidence supporting that an excess intake of vitamin B-12 can produce harmful effects. Medical reports have shown that vitamin B-12 can produce side effects and may contribute to serious health conditions in people with certain chronic diseases.

Evidence of Harmful Effects

Due to the insufficient evidence that supports the adverse effects of vitamin B-12 overdose, the Institute of Medicine of the National Academies, or IOM, does not specify the maximum level of daily intake that could pose a threat to health. The IOM warns that people should not overdose on vitamin B-12 because it may cause potential adverse effects.

Studies of Harmful Effects

According to Linus Pauling Institute at the Oregon State University, no significant side effects have been reported by individuals who received 1 mg of vitamin B-12 capsules daily or 1 mg of intramuscular injection monthly for the treatment of pernicious anemia. Individuals with pernicious anemia can't produce the sufficient amount of healthy red blood cells due to vitamin B-12 deficiency, thus vitamin B-12 medications or supplements would help correct the condition. The university explains that excess intake of vitamin B-12 produces only a very minimal amount of toxicity to the body because human tissues cannot absorb high doses of this water-soluble vitamin.

Reported Side Effects

Medical reports have shown complaints of mild diarrhea; inflammation, such as itching and swelling of the body; and peripheral vascular thrombosis, a condition in which clots developed in the arteries leading to the arms or legs by patients who received intravenous vitamin B-12 doses. Additionally, physicians have documented cases of pulmonary edema, a condition in which fluid accumulates in the lungs, and congestive heart failure, commonly known as heart failure, as potential side effects. The American Heart Association describes congestive heart failure as the heart's inability to pump enough blood to meet the needs of the tissues throughout the body, and generally this can result in the accumulation of fluid in the lungs, liver, eyes and legs.

Dr. Mary Mulvihill and her colleagues point out vitamin B-12 and its potential to increase blood volume as a possible explanation to the contribution of these aforementioned conditions. Due to the lack of reliable evidence of health safety of large intakes of vitamin B-12 during pregnancy, MayoClinic.com suggests that pregnant women should avoid excess intake of vitamin B-12 as well.