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Vitamin B12: Cure-all or placebo?

Published: February 2012

“Hey, Doc, I’ve been dragging lately. How about a shot of B12? My mother-in-law had one and it put her on top of the world.”

Primary-care practitioners have been fielding such requests about this reputedly potent fatigue-fighter for at least a half-century. So you would think the revitalizing properties of vitamin B12 for healthy individuals would be well established by now. Well, think again. And you might also be surprised by how many people truly are vitamin B12 deficient.

The oversized reputation of vitamin B12 probably stems from long-ago research at Boston City Hospital that established the vitamin’s importance in relieving the fatigue associated with pernicious anemia, a disease that impairs the absorption of vitamin B12 from food.

The injectable red liquid quickly gained a reputation as a magic antidote for everyday fatigue in otherwise healthy people with normal vitamin B12 blood levels. This belief has persisted despite the lack of good scientific evidence for its use as an all-purpose energizer. In 1985 a National Ambulatory Medical Care Survey recorded about 2.5 million vitamin B12 injections, of which less than 400,000 were for diagnoses compatible with B12 deficiency disorders.

When to treat

It wasn’t until 1973 that the first randomized controlled clinical trial—involving 29 subjects and lasting only six weeks—took place. The participants, all with normal vitamin B12 blood levels, were given either a twice-weekly dose of the vitamin or a placebo for two weeks, followed by a rest period of two weeks, and a final two-week phase in which the vitamin and placebo recipients were secretly switched.

The study was flawed because only the group that received the vitamin first was analyzed. No statistical differences were noted in appetite, sleep patterns, and fatigue, but those initially given vitamin B12 were “happier” and “felt better.”

In another small randomized controlled study from 1989, five people with chronic fatigue syndrome were given a mixture of liver extract, folic acid, and B12, or a placebo, at different phases of the month-long study. Their fatigue levels were the same regardless of which phase they were in.

The role of vitamin B12 has been much better established as replacement therapy for people who are really deficient in the vitamin, which is essential for DNA synthesis, red blood cell development, peripheral nerve integrity, and cognitive function. B12 is not made in our bodies and can be obtained only from animal proteins (or artificially fortified grains). Once it’s ingested, stomach acid is necessary to pry it from food, after which the vitamin combines with something called intrinsic factor, a substance made in the stomach, before eventually being absorbed in the small intestine.

Whom to test

According to the 2001-2004 National Health and Nutrition Examination Survey, 3.2 percent of those over the age of 50 have true vitamin B12 deficiency. More in that age group are at risk; up to 30 percent lack sufficient stomach acid to extract B12 from food. Even greater decreases in stomach acid can occur in patients using proton pump inhibitors, such as omeprazole (Prilosec and generic) and esomeprazole (Nexium); and H2 blockers, such as famotidine (Pepcid and generic) and ranitidine (Zantac and generic).

Another medication associated with vitamin B12 deficiency is the diabetes drug metformin (Glucophage and generic). Strict vegetarians should consume extra B12 from either fortified food or supplements. Malabsorption due to inflammatory bowel disease (Crohn’s and regional ileitis) can also cause a deficiency.

There are no current guidelines on screening for B12 deficiency in people without symptoms. Still, it seems reasonable to check high-risk individuals, especially since oral vitamin B12 has now been shown to be as effective as injected B12, and in any event supplementation is not harmful.

Ask your physician to check your vitamin B12 level if you:

are over 50 years old
take a PPI or an H2 blocker
take metformin
are a strict vegetarian
have inflammatory bowel disease

Marvin Lipman, M.D.

Chief Medical Adviser and Medical Editor

Editor's Note: Marvin m. Lipman, M.D., has been Consumer Reports’ chief medical adviser since 1967. He is a diplomate of the American Board of Internal Medicine (certified in endocrinology and metabolism) and is clinical professor emeritus of medicine at New York Medical College.