This is a very, very, very serious question most often posed by pitiful pundits who, by the way, happen to be selling B-12 supplements. The October issue of the European Review of Medicine and Pharmacological Science (2011 Oct;15(10):1176-81) found absolutely no correlation exists between vitamin B12 and quality of life in healthy young adults.
Researchers tested 359 healthy college students between the ages of 18 and 30 for their Vitamin B-12 blood levels and then tested each subject on two different medical scales, the Physical Summary (PCS) and the Mental Component Summary (MCS). Their quality of life (QOL) was then quantified on a test developed by Abbott Labs; the IMx system.
"We conclude that no correlation exists between B12 levels and QOL scores among young adult healthy populations."
The problem with B-12 assessments is that Vitamin B-12 is produced by bacterial action and is not stored in the blood where it is measured; B-12 is stored in the liver.
Furthermore, the test currently in use to detect so-called deficiencies is poorly designed.
In the March 2012 issue of the Annals of Clinical Biochemistry, researchers confirmed that the traditional test for B12 deficiency is flawed due to the poor sensitivity of the currently used methylmalonic acid assay. Instead, they determined that a new assay which relies upon holotranscobalamin should be adopted in clinical assessments. This conclusion was made after comparing both assays on blood samples from 360 human subjects.
Many vegetarian writers, doctors, and scientists believe that Vitamin B-12 supplements are critical to the health of vegans. I believe this to be pure nonsense. In 1996, Victor Herbert determined that Vitamin B-12 deficiency is rare among vegans, even though most do not take supplemental B-12. His landmark work was published in the American Journal of Clinical Nutrition, vol. 59, pp. 1213S-1222S. Herbert wrote:
"To a great extent, B-12 is recycled from liver bile in the digestive system...The enterohepatic circulation of vitamin B-12 is very important in vitamin B-12 economy and homeostasis...bodies reabsorb 3-5 mcg of bile vitamin B-12. Because of this, an efficient enterohepatic circulation keeps the adult vegan, who eats very little vitamin B-12, from developing B-12 deficiency disease..."
When the subject is B-12 deficiency, T. Colin Campbell, author of The China Study, makes these six points:
"Contrary to the most recent U.S. Dietary Guidelines, B12 can be found in plants."
"Organically grown plants contain higher levels of B12 than plants grown non-organically with chemical fertilizers."
"Plant roots are able to absorb certain vitamins produced by soil microorganisms, thus suggesting that plants grown in healthy soil, full of microflora and microfauna, are more nutritious."
"Vegans - and anyone else - should be able to obtain B12 by consuming organically grown produce."
"Evidence that plants obtain vitamins from the soil has been available for several decades."