Clinical Trial of the Vegan Diet and B12
“A group of 20 omnivores agreed to follow a vegan diet for 5 years. Half the group ate B12 fortified foods and the other half did not. Neither group took B12 supplements. The amount of B12 received via fortified foods was not measured. After 5 years, B12 levels in the group using fortified foods went from about 340 to 310 pg/ml. B12 levels went from about 290 to 220 pg/ml in the group not using fortified foods. Only two participants had B12 levels fall below 200 pg/ml, traditionally considered the cutoff for B12 deficiency, and they were both from the unfortified foods group.”
The most interesting finding of this study may be that they convinced 20 omnivores to go vegan for five years! They claimed that all 20 participants adhered to the diet.
I was also surprised that they conducted a study that was likely to induce a nutrient deficiency. They might have told the participants that if they started feeling the symptoms of B12 deficiency they should do something about it, but there appeared to be no monitoring between months 24 and 60.
The researchers did not measure homocysteine or methylmalonic acid levels at any point, so it is not clear what level of B12 deficiency these subjects actually had. There is reason to think that B12 levels as high as 400 pg/ml are required to minimize homocysteine, although this likely depends on how much folate someone gets as folate also reduces homocysteine.
Mądry E, Lisowska A, Grebowiec P, Walkowiak J. The impact of vegan diet on B-12 status in healthy omnivores: five-year prospective study. Acta Sci Pol Technol Aliment. 2012 Apr 2;11(2):209-12. | link