Vitamin B-12 (cobalamin) is a complex molecule that contains the minerals cobalt and phosphorous. The vitamin is an important co-enzyme required for the metabolism of carbohydrates, proteins and fats. It functions together with folacin and plays an important role in DNA synthesis and the maturation of red blood cells. Severe vitamin B-12 deficiency can result in pernicious anaemia and can lead to irreversible neurological deterioration.
Plants do not produce vitamin B-12 and neither do animals. The vitamin is produced by bacteria, and animals thus obtain their supply from their intestinal bacteria, or from eating the flesh of animals. The bacteria that produce vitamin B-12 are very sensitive to acid and so they are confined to intestinal regions that have a low acidity. For ruminants there is thus no problem, as the rumen contains an alkaline medium and ample bacteria which can produce the vitamin. In non-ruminant plant eaters such as rodents and rabbits, the bacteria that produce vitamin B-12 are mainly confined to the posterior portions of the intestinal tract where absorption of the vitamin is minimal. They solve this problem through the phenomenon known as coprophagy (eating one’s own excreta), and thus satisfy their vitamin B-12 demands. Carnivores, in turn, obtain their supply of vitamin B-12 from the stored vitamin in the flesh of animals, but they also prefer to eat the rumen content of their prey, which is rich in nutrients, including vitamin B-12.
The human digestive tract also contains the bacteria which produce vitamin B-12, but these bacteria are again largely confined to the colon, where absorption is minimal or non existent because of the absence of the intrinsic factor required for its absorption.. The bacteria are there, and b -12 is produced in the colon as was proved by correcting vitamin B-12 shortages with extracts of human stools.12 Short of coprophagy, there is thus no other way of obtaining vitamin B-12 but through the diet. As plants do not produce vitamin B-12 (although there is evidence that some plants may produce small amounts), the vegan vegetarian can only obtain this vitamin from food that is contaminated with bacteria, or from the small amounts which are available from the intestinal bacteria. Vegan vegetarians have a high consumption of fibre, and as a consequence, they have higher concentrations of bacteria in the lower portions of the small
intestine where B-12 can still be absorbed because of a high enough concentration of the necessary intrinsic factor.13 The bacterial flora in the mouth can also contribute to the vitamin B-12 requirements of vegans.13 The more alkaline the diet, the higher the intestinal bacterial concentration will be, and great care should thus be taken to ensure proper food combinations and to consume correct proportions of alkaline to acid forming foods.
The requirements for vitamin B-12 are extremely low, and nobody needs more than 1 mg/day. It has even been found that doses as low as 0.1 mg/day could reverse symptoms of deficiency.14 Moreover, vitamin B-12 is reabsorbed very efficiently from bile and thus has the longest reserve capacity of all vitamins, and this explains why it takes up to 20 years to run out of vitamin B-12 after one stops consuming it. In cases of disturbed absorptive capacity, mostly because of intestinal infections or a reduction in the production of the intrinsic factor required for the absorption of vitamin B-12 it will however take only 3 years to run out of vitamin B-12.14 The production of the intrinsic factor is normally impaired when portions of the stomach have been operatively removed, or if there is an infection of the stomach mucosa (gastritis). This probably explains why cases of vitamin B-12 deficiency are rarely reported in the literature.6 Vegan vegetarians need thus not panic over the issue, but they should be aware of the possible shortages which may arise, particularly in small children, and should supply the lack in the form of a supplement or foods fortified with cobalamin. Fortified soy milk or vitamin B-12 fortified nutritional yeast are possible sources for this purpose. It is important to ensure sufficient dietary B-12 in the case of infants that are breast fed, as B-12 reserves will decline over time in mothers that breast feed if reserves are not maintained.13 For peace of mind in this regard, it would be prudent to have a serum analysis done to determine the concentrations of B-12 in the blood, as this is the most accurate way of determining B-12 status.
When purchasing fortified foods or supplements, it is important to note that the product contains cobalamin, and not some analogue of the vitamin. Most of the claims of B-12 content on products are incorrect, as the analysing techniques used do often not distinguish between analogues and the active B-12 which is cobalamin. Fermented soy foods, such as tempeh, also do not contain vitamin B-12, and neither does Spirulina, which is often sold in health shops as a source of vitamin B-12.14 Spirulina may even make matters worse because it contains analogues which may interfere with normal absorption of cobalamin.