(The following is an excerpt from the FAQ Chapter in The “Plan A” Diet)

Vitamin B12, also called cobalamin, is a compound produced by bacteria that can live in an environment without oxygen. In days gone by, bacteria-based B12 found in the soil would be consumed by humans eating plants which still had a bit of dirt attached. But because our society now fervently washes fruits and veggies to wipe out any trace of bacteria, we no longer get proper levels of B12 from our food—nor from our chlorinated water supply.

Vitamin B12 is important for the production of red blood cells, the formation of DNA, and for maintaining the normal function of the brain and nervous system. Animals and plants don’t have the enzymes to produce B12, but animal tissues do have the ability to store B12 when it’s consumed from foods—which is why meat, poultry, eggs, fish, and dairy foods are typically recommended as sources of B12. Just as with calcium, animals have B12 in their systems because they’ve consumed it from their food.

So where does that leave those of us who only consume plant foods? Fortunately, our bodies can store B12 for several years too, so there’s no need to run out and immediately purchase supplements; but to be safe, it’s important to take a vitamin B12 supplement.

Meat-eaters require supplementation just as much as plant-eaters do, as they often develop B12 deficiency for many reasons as well—poor absorption due to atrophic gastritis, weight loss surgery, Crohn’s disease, pancreas dysfunction, and the prolonged use of certain medications, just to name a few. For those reasons, B12 supplementation is recommended by the Institute of Medicine for all adults over the age of 50, regardless of their diet.

How much vitamin B12 should we take? The average adult needs only about 2.4 micrograms (mcg) per day, but you’ll notice that supplements are sold in much higher dosages. The experts’ opinions vary on the appropriate dosage—the goal is to take enough to keep our levels at a healthy range without incurring any side effects from taking too much. Dr. John McDougall recommends taking 500 mcg weekly, in either the hydroxyl, methyl, or adenosyl forms; he suggests avoiding the cyano form due to possible toxicity issues. Dr. Thomas Campbell recommends taking the smallest dosage in either cyano or methyl form, perhaps a couple of times a week, and having your blood checked to make sure it’s sufficient. And because our bodies can only absorb a small amount of B12 in any pill, Dr. Michael Greger recommends 2500 mcg of the cyano form once a week, in a sublingual (under the tongue), chewable, or liquid supplement.

As you can see, the recommendations for B12 supplementation vary. I personally take 1000 mcg of methyl B12 once per week and have had good results to date. If you have health concerns that may affect your B12 absorption ability, please discuss the matter with your doctor.