Vitamin B12, also named cobalamin, is a member of the B complex of vitamins. All the B vitamins, including vitamin B12 are water soluble, and excess amounts of vitamin B12 that are not used by the body are usually excreted in the urine. As a result, overdosing on vitamin B12 is extremely rare. However, even in small doses, vitamin B12 supplements may cause side effects.
Mild Side Effects
Vitamin B12, even taken in small doses, has been reported to cause a variety of mild side effects. A common mild effect is a rash, or dry, itchy skin. In some cases, the rash may become more troublesome, developing into a widespread rash, also known as exanthema, or developing into a series of red welts, also called urticaria. In rare cases, pustules or papules may form on the skin. These symptoms may last up to four months after taking vitamin B12 supplements, warns the Mayo Clinic. Diarrhea has also been reported following the use of vitamin B12 supplements.
Severe Side Effects
In some cases, more severe side effects can result from vitamin B12 supplements, such as the formation of blood clots in the veins of the arms or legs, a condition known as peripheral vascular thrombosis. Patients who undergo coronary angioplasty should avoid vitamin B12, because large doses of vitamin B12 and B6 are often given after the procedure, and taking more vitamin B12 can increase the risk of complications. Vitamin B12 contains the metal ion cobalt, which can cause allergic reactions in some people. Symptoms of an allergic reaction include nausea, dizziness, difficulty breathing and swelling of the face, hands, neck or throat.
Tolerable Upper Intake Level
The Tolerable Upper Intake Level, UL, is the limit set by the Food and Nutrition Board of the Institute of Medicine on how much vitamin B12 should be taken daily. Doses of up to 1000 micrograms per day have been used to treat vitamin B12 deficiency, and have caused no apparent increase in the risk of side effects, according to the Linus Pauling Institute at Oregon State University. As a result, the Food and Nutrition Board has not set a UL for vitamin B12.
Recommended Dietary Allowance
The Recommended Dietary Allowance of vitamin B12, RDA, is the daily intake of vitamin B12 recommended by the Food and Nutrition Board to met your body's nutritional requirements. The RDA for infants ages zero to six months is 0.4 micrograms per day, and rises to 2.4 micrograms per day for males and females aged 14 years and older. Most people meet this RDA through a normal, healthy diet.
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