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    You Ask, I Answer: Vitamin B12

    As a vegetarian (vegan most days) I know I have to supplement my diet with vitamin B 12. However, I’m really puzzled about something.

    The best sources (non-veg) of vitamin B 12 are mollusks, snapper, calf’s liver, lamb, venison, etc. If these animals are able to produce vitamin B 12 in their tissues, why aren’t we?

    — Jennifer Armstrong
    Saratoga Springs, NY

    Great question.

    Vitamin B12 is produced by bacteria in animals’ — yes, that includes humans — digestive tracts. However, since this occurs in our large intestine, it is past the point of absorption (nutrient absorption takes place in the small intestine).

    You may be wondering, then, why Vitamin K — also synthesized by bacteria in the large intestine — is absorbed with no difficulty.

    Simple. Our colons contain Vitamin K receptors which aid in the absorption process. Keep in mind, though, that we do not produce enough vitamin K to meet the Recommended Dietary Allowance, so we must get some from food.

    While we’re on the subject of B12, I want to point out other important factors regarding its consumption and absorption.

    Too often, I see various forms of algae and seaweed described as “good sources of B12”, which is inaccurate.

    What those foods contain are B-12 analogues — compounds that mimic real B12 and compete with it for absorption (bad news!).

    Some fermented soy foods (natto, tamari, and miso) contain real B12, but the amount is so insignificant that it is really a moot point.

    A much better idea for vegans and vegetarians is to supplement B12 through fortified foods (i.e.: certain brands of nutritional yeast, as well as most brands of non-dairy milks and cereal) or supplements.

    It is not only vegans who need to be concerned with B12, though.

    People with celiac disease need to be careful; gluten intake damages the microvilli in their small intestines, thereby inhibiting absorption of nutrients, including B12.

    Similarly, individuals who undergo total gastrectomy are at high risk of developing B12 deficiencies, as they lack intrinsic factor (a glycoprotein produced by the stomach and required for B12 absorption.)

    A large body of research has also established that B12 absorption capacity decreases with age, which is why it is often recommended that individuals over the age of 60 supplement B12.

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    2 Comments

    1. Jennifer Armstrong said on October 6th, 2008

      Thanks very much for the explanation, Andy.

    2. Kevin said on February 18th, 2012

      Great explanation! Hear too many vegan friends saying their kombucha/seaweed gets them their necessary b12

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