Myth about How Often Someone Needs B12

Some vegan advocates have emphasized that humans need only small amounts of B12 and that it can be stored in the body for years. It is true that, at the time they become vegan, some people have enough B12 stored in their livers to prevent overt B12 deficiency for a number of years. But, these stores cannot prevent mild B12 deficiency (elevated homocysteine levels).

Additionally, to build up such stores, it takes many years of consuming B12 beyond one's daily needs without using supplements. Many people have not consumed B12 beyond their daily needs for many years and so cannot rely on B12 stores to prevent overt deficiency for a few years.

The body is constantly losing small amounts of B12 and the length of time that any given molecule of B12 will stay in the body will vary based on a number of variables. So, your body might store it for a long period of time, or it might not store it at all.

Of course, this is an easy problem to solve by simply eating B12-fortified foods or taking a supplement.

Small Amounts of Animal Products Do Not Cure B12 Deficiency

There is evidence that B12 function cannot be restored to optimal levels by adding small amounts of animal products into the diet:

van Dusseldorp et al.¹ (1999, Netherlands) investigated whether moderate consumption of animal products is sufficient for achieving normal B12 function in 73 adolescents who had been strict macrobiotics (MAC) until 6 years old and then switched to a lacto-ovo-vegetarian (LOV) or non-vegetarian (NV) diet. 94 people who had never been macrobiotics or vegetarian were controls. Dairy supplied an average of ~ 1 µg B12/day for the MACs. They also ate fish, red meat, or chicken 2-3 times/week.

Thus, moderate animal product consumption was not enough to restore normal B12 status for 21% of these children (based on MMA levels).