Vitamin B12 is a generic name for a group of cobalamin vitamers that includes adenosylcobalamin, hydroxycobalamin, cyanocobalamin, aquacobalamin, nitrocobalamin and methylcobalamin. All vitamin B12 is produced by bacteria. Vitamin B12 is an important coenzyme to three key enzymes in human metabolism including homocysteine methyltransferase, methylmalonyl-CoA mutase and leucine aminomutase. Insufficient intakes of vitamin B12 cause reduced flux through the pathways involving these enzymes and this results in metabolic dysfunction. Vitamin B12 is interesting nutritionally because it is found only in tissues of animal origin. While some cobalamin-like substances have been identified in plants, evidence suggests that these compounds are either not absorbed or not recognised as vitamin B12 by the body. As a result of this vitamin B12 can only be obtained from tissues of animal origin which produces a problem for vegans. Lactovegetarians consume milk and eggs and as a result can often obtain some vitamin B12 in their diets.
A number of studies have analysed the diets of vegetarians in comparison to omnivores consuming mixed diets, and these results often highlight low intakes of vitamin B12 for the former. For example, in one study1 the diets of lactovegetarians were analysed chemically and compared to the diets of subjects eating a mixed swedish diet and a vegan diet, both of which had been examined previously. The intake of vitamin B12 was only ~1.4 μg per day for the lactovegetarians, which was below the recommended intake. However, the subjects showed no signs of deficiency suggesting that intake was great enough to prevent clinical deficiency. The intakes of other nutrients were adequate in terms of current recommendations, although this does not mean that the intakes were optimal. As would be expected the lactovegetarians had greater fiber intakes than omnivores consuming a mixed diet (the amount was actually three time higher). This is explained by the higher intakes of plant foods in the lactovegetarian diet.
Dr Robert Barrington’s Nutritional Recommendation: While lactovegetarians can clearly obtain some vitamin B12 from their diet, the consistently reported low intakes of this group suggest that a supplemental B12 tablet would be beneficial. The absence of any products of animal origin in the diets of vegans necessitates a vitamin B12 supplement. Any vegans not taking a vitamin B12 supplement will almost certainly be deficient in the vitamin. However, some vitamin B12 may be produced in the gut of humans, and this may prevent outright deficiencies developing in vegans who do not supplement.
RdB
