B-12 Facts and Myths


Separating fact from fiction

B-12 (cyanocobalamine or methylcobalamine) is critically important in human nutrition.  A deficiency of B-12 can occur by several mechanisms and is not as uncommon as you might imagine.  B-12 deficiency can cause a number of serious, potentially permanent, even fatal diseases, and B-12 is a relatively harmless supplement.  That said, excess vitamin B-12 does cause human disease, and excess B-12 does not improve energy or assist in weight loss.

Most humans only require 2 or 3 micrograms of B-12 a day in their food for good health. B-12 is plentiful in animal products such as fish, meat, and dairy products.  Deficiencies arise in Vegans (vegetarians who do not consume dairy or eggs), other malnourished people such as alcoholics, or people with poor absorption of B-12 in the intestines.  Examples of people with poor absorption include those who have had stomach or intestinal surgery, those who take pills to block the production of stomach acid, and people with chronic intestinal diseases like Crohn’s disease.  Some medications, like the diabetic medicine, Metformin, or anti-seizure medicines also predispose people to B-12 deficiency, perhaps by using up the vitamin more rapidly than usual.  B-12 deficiency is also seen in an unusual medical condition called pernicious anemia, which is more common in older people.

B-12 deficiency results in the body having trouble making blood properly and also affects the brain and the nerves, sometimes permanently.  Doctors can find or suspect B-12 deficiency based on blood tests, often before a patient feels symptoms.  Symptoms can include such things as fatigue, looking very pale, problems with balance, numbness or weakness in limbs, confusion and psychiatric problems.  If you have any of the symptoms above, especially if you have one or more of the risk factors mentioned above, you should ask your doctor or health care provider to look for B-12 deficiency. 

People with risk factors for B-12 deficiency should also consider oral supplementation of the vitamin to prevent deficiencies.  Vegans or people with poor diets only need 2 or 3 mcg a day, so a daily multi-vitamin supplement is sufficient.  In contrast, people with poor absorption of B-12 due to surgery, disease, or acid-blockers should take 1000 to 2000 mcg a day, depending on the doctor’s advice.  The preferred form is Methylcobalamin rather than Cyanocobalamin to improve absorption and utilization.  At these high amounts of B-12, the special transport and absorption mechanisms of the human body are not needed, and the intestines can passively absorb enough B-12 without stomach acid, instrinsic factor or full length intestines.  People with risk factors or a history of deficiency should be monitored (have blood drawn) every 3-6 months initially and at least once a year after this to ensure that they have adequate levels of this critical vitamin.

            Some people still need to get shots of B-12, but these are uncomfortable, inconvenient and recently there has also been a shortage of the injectable B-12 due to manufacturing delays.  There is also a greater risk of side effects and over-dosage with the shots.  Sublingual (under the tongue) and intranasal forms of B-12 are also available for those who don’t get enough B-12 from oral vitamins.  The only people who definitely need the shots are those with symptoms due to severe deficiency (just for the initial treatment to get back up to normal levels) and those who are unable to keep up normal levels on just oral supplements.  Some people still choose the shots for other reasons.

            B-12 is a water-soluble vitamin.  This means that it is not stored in fat.  Instead the human body gets rid of excess in the urine.  This makes it a very safe vitamin under normal circumstances.  However, a recent study showed that a high oral intake of vitamin B-12 and B-6 increased the risk of hip fracture.  Shots have much higher doses and more side effects.

Unfortunately, although B-12 does not help weight loss in any way, or improve energy in healthy people,  some people still market B-12 shots for weight loss and energy, sometimes adding amino acids and giving the shot a fancy name.  Amino acids are the building blocks of protein and you eat plenty of these every day, so the tiny amount in the shot does absolutely nothing.  These so-called weight loss centers use it for the placebo effect of a shot.  The human body has very strong, but temporary, responses to placebos (pretend medicines).  Placebos often cause around a 30% “response rate” on subjective symptoms which are not measurable objectively.  Unfortunately, giving a normal person shots of B-12 several times a month, or even several times a week is actually dangerous. Not only can you get an infection or hit a nerve or blood vessel with the shot if not given properly, but excess B-12 can make you sick. Common side effects of B-12 overdose include headaches, anxiety, itching, swelling, nausea, diarrhea, joint pain, and balance problems.  Less common, but more severe, side effects include life-threatening allergic reactions (which can happen even if prior shots were fine), high platelet counts, blood clots, low potassium levels, fluid in the lungs and heart failure.

            In summary, B-12 is critical to good health, easy to get in regular foods, and safe to supplement with oral multi-vitamin pills.  People with risk factors for deficiency should discuss this with their health care providers.  Deficiencies should be treated and regularly checked.  And, although B-12 overdose is unusual, it can occur and cause symptoms in people given shots of B-12 inappropriately.

Dr. Chastanet hiking in the Grand Canyon Rachel Chastanet MD Dr. Chastanet is Board Certified in Internal Medicine and Obesity Medicine. She practices at Chesapeake Weight Loss & Aesthetics in Chesapeake, VA.

You Might Also Enjoy...

The Skinny on Skin Care

Healthy glowing skin is what we all strive for, however achieving the complexion we desire may seem a little daunting with all of the different skin care tips floating around. Where does one begin?