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Do You Know How to Recognize the Signs of B12 Deficiency?

Learn how shots and supplements differ and can help with B12 deficiency.

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“You can die of a B12 deficiency,” says Sally Pacholok, RN, the lead author of Could It Be B12?: An Epidemic of Misdiagnoses. While she isn’t suggesting that everyone rush out and get a B12 shot, Pacholok’s experience as a nurse has demonstrated that many serious B12 deficiencies are undiagnosed, leading to unnecessary drug prescriptions and suffering.

To help right these wrongs, she cofounded an educational website, B12 Awareness. “There’s a severe knowledge deficit in the health care community,” she says. For one thing, the possibility of a B12 deficiency is not even considered in many situations, especially in cases of depression, other mental disorders, and neurological problems. For another, when tests are done, they are typically inadequate and lead to a false conclusion that no deficiency exists.

What does vitamin B12 do?

B12 is an essential vitamin that is used to convert carbohydrates into fuel, maintain healthy nerve cells, make red blood cells, maintain the body’s genetic material, utilize iron, and produce compounds that affect the immune system and neurological function.

Symptoms of a shortfall can include fatigue, weakness, weight loss, loss of appetite, numbness or tingling in the hands or feet, a sore mouth or tongue, and neurological symptoms such as poor balance, depression, poor memory, confusion, and dementia. In infants, B12 deficiency can delay development and cause movement disorders. In both children and adults, a deficiency can underlie megaloblastic anemia, a blood disorder.

Who Is at Risk for Vitamin B12 Deficiency?

Since animal foods are the main dietary source of B12, some vegetarians and vegans should seek out foods fortified with the vitamin, or take supplements. Additionally, says Pacholok, there are several reasons why the body may not absorb adequate amounts of B12, including:

  • Low stomach acid, due to age or acid-suppressing medications;
  • Taking metformin, a diabetes drug;
  • Getting nitrous oxide for anesthesia;
  • Gastrointestinal conditions such as ulcers, Crohn’s disease, celiac disease, or other malabsorption syndromes;
  • Intestinal or bariatric surgeries; and
  • Eating disorders.

In addition, some people have a genetic polymorphism that prevents their bodies from moving B12 through the bloodstream. And people age 65 or older are at greater risk of atrophic gastritis, a condition that interferes with B12 absorption. Where absorption is a problem, shots may be the only option.

If you have a medical condition and suspect a B12 deficiency, Pacholok recommends getting tested before taking any supplements, which would skew results-for serum B12 and methylmalonic acid, a substance that is elevated when B12 is lacking.

Should you get vitamin B12 shots?

“If you want shots because they make you feel better, that’s okay,” says Holly Lucille, ND, RN, a naturopathic doctor in Los Angeles ( “It’s a pretty safe injection to get without testing.”

Any excess of the vitamin is simply excreted and is not toxic. In fact, the risk of toxicity is so low that the Institute of Medicine, which sets safe upper limits for nutrients, did not set such a limit for B12 because, it wrote, “no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals.” But more doesn’t necessarily mean better, either.

You can also get shots and take supplements in between, says Lucille. However, she adds, sublingual B12-which is absorbed in the mouth, not the digestive system-may be just as effective if you aren’t treating a medical condition.

Lucille recommends methylcobalamin, the “active” form of B12. Cyanocobalamin, the most common type of B12, must be converted into the active form in your body, and not everyone does this efficiently. Doses range from 500 to 5,000 mcg daily, or at least three times per week, with the higher dose after age 50.

Sublingual B12 may be just as effective [as B12 shots] if you aren’t treating a medical condition.

Can B12 Trigger Acne?

In some people, too much B12 from supplements, in either an injected or oral form, can trigger acne. This has been known for some time, but a recent study at the University of California, Los Angeles, has begun to shed some light on the underlying mechanism.

When researchers gave B12 shots to 10 healthy people, one of them broke out with acne a week later. Analysis of naturally present bacteria in their skin showed that B12 changes the way some bacteria behave, and in some cases, those changes result in an acne flare-up-but it’s easily reversible.

“I have seen, in the research and in my own clinical experience, that a decrease in the dosage has corrected the acne,” says Lucille. Or, you may need to stop taking supplements for a while. How long depends on your individual reaction. There isn’t a hard and fast rule.