Vitamin B12 poisoning is so rare and the substance considered so nontoxic that a maximum daily dosage limit does not exist for the vitamin, according to the eMedTV website. However, the vitamin can produce negative side effects in certain cases, even if you take an amount equivalent to the recommended dose. The recommended daily dose of vitamin B12 for people age 14 and older is 2.4 mcg.
Side Effects
Possible side effects from vitamin B12 include blood clots in the legs, diarrhea and a sensation of swelling throughout the entire body, eMedTV and the Mayo Clinic website report. Side effects can also occur in the form of an allergic reaction, with itching, a rash or hives, breathing problems, wheezing and a swollen throat, lips or mouth. Symptoms that mimic an allergic reaction are more likely if you are sensitive to cobalt or cobalamin.
Treatment Side Effects
Problems can arise from treatments that include high amounts of vitamin B12, according to the Mayo Clinic site. Such treatments include those for a vitamin B12 deficiency or megaloblastic anemia, a blood disorder marked by unusually large red blood cells. Deficiency treatments can unveil polycycthemia vera, a condition marked by an increase in number of red blood cells and blood volume. Megaloblastic anemia treatments can lead to gout, the masking of a folate deficiency and a low level of potassium in the blood, the latter of which can be fatal.
Other Precautions
People who receive coronary stents as part of their angioplasty treatments should steer clear of vitamin B12, the Mayo Clinic site reports. These patients already receive a dose of vitamin B12, vitamin B6 and folic acid intravenously as part of the procedure, and consuming additional amounts of these particular nutrients can lead to new blockages in their arteries. People suffering from the hereditary atrophy of the optic nerve, a condition known as Leber's disease, are also safer without vitamin B12. The vitamin can lead to rapid and drastic optic atrophy.
Cosiderations
Just as an overdose of vitamin B12 is rare, so is a deficiency, according to the Mayo Clinic site. Your body can store a backup reserve of vitamin B12 over several years, although you can experience a deficiency if your body can no longer absorb the vitamin. Pernicious anemia, a disease that blocks vitamin B12 absorption in the intestines, can be the cause of a deficiency, as can following a strict vegan or vegetarian diet. Elderly people are also a greater risk of a vitamin B12 deficiency than are younger adults.
References
- MayoClinic.com; Vitamin B12; July 2011
- eMedTV; Vitamin B12 Toxicity; Kristi Monson and Arthur Schoenstadt; October 2008
- National Center for Biotechnology Information's PubMed Health; Megaloblastic Anemia; May 2011
- National Center for Biotechnology Information's PubMed Health; Hypokalemia; August 2009
