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Metabolism and Metabolic Studies
Abbreviations: AAFC, Agriculture and Agri-Food Canada; PDV, portal-drained viscera
Among B vitamins, vitamin B12 occupies a very special niche. This vitamin is produced only by bacteria and archaebacteria if Co supply is adequate. As opposed to other B vitamins, it is neither synthesised nor used by fungi and plants(1). Therefore, in human diets, the sole natural source of vitamin B12 comes from animal products. Among animal products, those from ruminants are particularly rich in vitamin B12, the vitamin being naturally synthesised by ruminal microflora using Co as an essential precursor and then absorbed and stored in the liver and muscles (meat) of the host or secreted in its milk(2).
In humans, vitamin B12 deficiency affects cell division and may lead to megaloblastic anaemia and neuropathy(2). In the presence of vitamin B12 deficiency, increasing folic acid supply cures anaemia but not neurological symptoms, then, by masking haematological symptoms, it could delay the diagnosis of vitamin B12 deficiency until neurological damages are irreversible. Consequently, over the last decade, since folic acid fortification of flour became mandatory in many Western countries, including Canada and USA, there has been a renewed interest in the evaluation of vitamin B12 status in human populations according to folic acid provision(3,4).
Vitamin B12 status is correlated with vitamin B12 intake in humans(5-7). Vegetarians had lower vitamin B12 status than omnivores(7,8). However, dietary sources of the vitamin also seem to matter. For example, vitamin status of vegetarians was positively correlated with their intake of dairy products, especially milk, but not of eggs or seafood(8). Among adults not using vitamin supplements, the relationship between plasma concentration of the vitamin and its intake from dairy products is similar to the relationship observed with the intake from cereals fortified with vitamin B12. However, the relationship with intake from meat, poultry or fish is weaker(5). A Norwegian study showed that plasma vitamin B12 increases with...