Vitamin B-12 is an important nutrient that plays a role in various vital processes, such as the synthesis of DNA, and the metabolism of protein and fat. It is an essential vitamin, meaning that we must get it from our diet or supplements because our bodies cannot produce it on their own. Due to its significance, B-12 is added to many foods in order to help consumers meet their daily requirements for the vitamin. However, it is still possible to have too much vitamin B-12 in your system, and this can lead to a wide range of negative effects, some of which are serious.
Dermatological Symptoms
Though vitamin B-12 is considered non-toxic, it can still have certain minor side effects, even when taken in small amounts. These include skin complications such as increased acne, itching, rash or dry skin. In some cases, these may deteriorate into slightly more serious skin conditions such as transitory exanthema, and urticaria or hives, MayoClinic.com explains. These problems may persist for a time; some patients experience lingering effects up to four months after taking vitamin B-12 supplements.
Cardiovascular Symptoms
In rare cases, large doses of vitamin B-12 taken intravenously can lead to potentially serious cardiovascular complications, Drugs.com reports. The first signs of these usually involve pain, tingling or numbness in the arms and legs and difficulty breathing. Some patients have experienced peripheral vascular thrombosis, where clots form in a blood vessel, or congestive heart failure. This is because vitamin B-12 delivered through injection can potentially interrupt the blood flow to vital organs such as the heart and lungs. Cases of pulmonary edema have also been reported.
Gastrointestinal Symptoms
Mild transient diarrhea is one of the more common potential symptoms of excessive vitamin B-12 consumption. These may be accompanied by dyspepsia, nausea and vomiting, Drugs.com notes. An exceedingly rare case of bezoar, a small, stony secretion formed in the intestine, was reported in an elderly patient who had a history of several gastrointestinal injuries. However, elderly individuals are more at risk for vitamin B-12 deficiency than they they are for an overdose.
Dosage
The recommended daily allowance for vitamin B-12 is 2.4 micrograms for men and women over 14 years of age, the Office of Dietary Supplements notes. For pregnant and lactating women, it is 2.6 mcg and 2.8 mcg, respectively. Many vitamins and minerals have a "tolerable upper intake level" set by the Food and Nutrition Board of the Institute of Medicine. However, since high oral doses of B-12 do not seem to cause an increase in the risk of side effects, no such limit has been set for this vitamin.
Allergic Reactions
Some individuals may have a hypersensitive, allergic reaction to vitamin B-12. These symptoms may include swelling of the face, throat, neck and hands, difficulty breathing, abdominal pains and cramping and heart palpitations. Though it is less common, there have also been cases of anaphylaxis -- a severe, life-threatening allergic reaction that requires immediate medical attention -- related to B-12.
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