VITAMIN B12 IS FOUND mainly in meat, poultry, ish, eggs and dairy. So those who follow diets that avoid or limit animal products are at greater risk of having inadequate amounts. Nevertheless, a full-blown B12 deficiency due to poor intake is rare, as stores of vitamin B12 can last in the body for two to four years without being replenished – if you switch to a vegan diet, a deficiency may take time to show.