Vitamin B12 (cyano-cobalamine) deficiency causes pernicious anemia which is characterized by weakness, loss of appetite, poor memory and depression. The vitamin itself is not really deficient but it is not properly absorbed by the body.

This is more likely to occur in people who lack a chemical called the intrinsic factor (which enables the absorption of B12), those with gastritis or have undergone stomach surgery, and strict vegetarians who don't consume milk or dairy products, eggs and other animal foods. These are the only cases where vitamin B12 supplementation is required.

But some bad physicians have the habit of giving "weak, tired" patients vitamin B12 injections even though they don't have pernicious anemia. The shots themselves are generally harmless (vitamin B12 is nontoxic except to your wallet) but a few do develop severe allergic reactions from this useless practice.

"It has been the unfortunate practice of many physicians to administer monthly B12 injections for tiredness, undiagnosed anemia and other vague symptoms. The dose usually given is 1,000 micrograms, 10 times the usually recommended injectable dose and about six months' worth of B12 in terms of the usual daily rate,” according to Drs. Harold M. Silverman, Joseph A. Romano and Gary Elmer in “The Vitamin Book: A No-Nonsense Consumer Guide.”

“This practice is costly, unnecessary and potentially dangerous because it exposes the patient to the possibility of reactions lo the injections. Allergic reactions to B12 injection can involve itching, redness and swelling and, in rare cases, serious drug reactions," they said.

Contrary to popular belief, vitamin B12 won't improve your memory unless you are deficient in this vitamin which happens only in the cases I cited above. So be wary of physicians who prescribe them without first finding the cause of your problem. As Jane Brody, award-winning health columnist of The New York Times, said in her “Nutrition Book”:

"They leave you with nothing more than a sore butt, a diminished purse, and, possibly, a failure to diagnose the true cause of your symptoms."

In summary, if anyone prescribes vitamin supplementation for your disease, avoid that person unless you are truly suffering from a vitamin deficiency. The above conditions don’t require nor can they be treated by megavitamin therapy.

Moreover, in cases where a vitamin deficiency is evident and is responsible for certain symptoms, the cure lies in correcting one's diet rather than popping pills.

The case against megavitamin therapy was neatly summed up by Dr. Samuel Valarub in the Journal of the American Medical Association who said "Not only is it an insult to the intelligence and an injury to the pocketbook, it is also a threat to health."

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