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To B12 or not to B12
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People are baring their arms and hips to get injections of Vitamin B12, and it may be worth the trouble, but only if you're in this one group. And pregnant women should monitor their intake, a new study suggests. - photo by Jennifer Graham
To B12 or not to B12, that is the question for people seeking to lose weight and restore flagging energy.

A quick-release shot of the vitamin has become a popular offering at weight-loss clinics and on Groupon, where people can snap up six B12 injections for about $35. But will it do anything special for you, or just fill your toilet with vitamin water? And could high levels of the vitamin be dangerous?

Time magazine answered the questions with the help of Dr. Roxanne Sukol, medical director of the Cleveland Clinics Wellness Enterprise. She said the B vitamins there are eight are essential for cell respiration, meaning they enable the body to take in oxygen. When our cells don't get enough, our energy dips, our mood darkens and our laser-focus dims.

Inadequate amounts of B12 (and B6) can also cause anemia, a chronic shortage of the red blood cells that shuttle oxygen to body tissue.

We obtain B12 when we eat meat, poultry, shellfish, eggs and dairy products. And unlike Vitamin C, our bodies can store it. But if we're not consuming enough animal protein, or if we're deficient in a protein that helps us absorb B12, we may need an extra source.

In addition, people who regularly take drugs for heartburn, acid reflux or ulcers (such as Prilosec or Tagamet) may also be deficient, The New York Times has said. And vegans are at particular risk, according to Time.

But other people might want to give supplementation a try if they're frequently fatigued or have trouble focusing. One study has suggested up to 40 percent of Americans, particularly the elderly, may be deficient in B12; another gives a range of 1.5 to 15 percent.

Injections of B12 have been shown to be beneficial for people who have fibromyalgia and myalgia encephalomyelitis. But otherwise, if you're going to try a supplement, a pill is just as good as a shot, Time said, noting that because it's water-soluble, the vitamin is safe, even in high doses, for the general population.

Pregnant women, however, should pay close attention to their intake.

One explosive new study has suggested a link between high levels of folate and B12 to autism, although one doctor writing in The Atlantic cautions that the claim is "extremely premature" and should not discourage women from taking prenatal vitamins.

How much do we need? The National Institutes of Health advise 2.6 micrograms (mcg) daily for pregnant women and 2.8 mcg for breastfeeding moms.

For adults and teens, the requirement drops to 2.4 mcg; for children 9-13, 1.8 mcg; and children 4-8, 1.2 mcg. Children 3 and younger need less than 1 mcg.

Despite the claims of some weight-loss clinics, don't expect to drop pounds just by taking a supplement.

"Everybodys looking for a shortcut," Dr. Brent Bauer, director of the complementary and integrative medicine program at Mayo Clinic, told Markham Heid of Time. B12 supplementation has its benefits, but its not a solution for weight loss.