Achieving an adequate B12 intake is easy and there are
several methods to suit individual preferences. Absorption of B12 varies from about 50%, if about 1 microgram
or less is consumed, to about 0.5% for doses of 1000 micrograms (1 milligram) or above. So the less frequently
you consume B12, the higher the total amount needs to be to give the desired absorbed amount.
Frequent use of foods fortified with B12 so that about
one microgram of B12 is consumed three times a day with a few hours in between will provide an adequate amount.
Availability of fortified foods varies from country to country and amounts of B12 vary from brand to brand, so
ensuring an adequate B12 supply from fortified foods requires some label reading and thought to work out an
adequate pattern to suit individual tastes and local products.
Taking a B12 supplement containing ten micrograms or more
daily provides a similar absorbed amount to consuming one microgram on three occasions through the day. This
may be the most economical method as a single high potency tablet can be consumed bit by bit. 2000 micrograms
of B12 consumed once a week would also provide an adequate intake. Any B12 supplement tablet should be chewed
or allowed to dissolve in the mouth to enhance absorption. Tablets should be kept in an opaque container. As
with any supplement it is prudent not to take more than is required for maximum benefit, so intakes above 5000
micrograms per week should be avoided despite lack of evidence for toxicity from higher
All three options above should meet the needs of the vast
majority of people with normal B12 metabolism. Individuals with impaired B12 absorption may find that the third
method, 2000 micrograms once a week, works best as it does not rely on normal intrinsic factor in the gut.
There are other, very rare, metabolic defects that require completely different approaches to meeting B12
requirements. If you have any reason to suspect a serious health problem seek medical advice
Symptoms of B12 deficiency
Clinical deficiency can cause anaemia or nervous system
damage. Most vegans consume enough B12 to avoid clinical deficiency. Two subgroups of vegans are at particular
risk of B12 deficiency: long-term vegans who avoid common fortified foods (such as raw food vegans or
macrobiotic vegans) and breastfed infants of vegan mothers whose own intake of B12 is low.