Doctor's Note

More on Vitamin B12:

For further context, check out my associated blog post: Vegan B12 deficiency: putting it into perspective.

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  • Michael Greger M.D.

    Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on vitamin B12. Also, there are 1,449 other subjects covered in the rest of my videos–please feel free to explore them as well!

    • Bill

      Can you advise of any natural fruit and vegetables with B12 content?

      • Toxins

        Hello Bill

        Sadly, since b12 is a product of bacteria, b12 is not found in plant sources. The only healthy and safe way to get adequate b12 is through supplementation, and I say “healthy and safe” to mean that animal sources contain b12, but the health detriments of consuming these products far outweigh the benefits. View this video on b12 and another necessary supplement!

    • Chronic Crohn’s Cosmic-Christ

      Hi, I know B12 isn’t found in any telluric flora; mushrooms aren’t plants though, is their B12 in shiitake mushrooms or any other fungi?

  • Hi Dr. Greger! I first wanted to thank you for this very informative site. I intend to discover much more useful information as time goes on…

    But for the moment I am curious – Of course I don’t intend to stop taking B12… But your video mentioned well water carrying B12, and I’m on well water – Wondering if I did drink several glasses of water per day – Would that be enough to supplement if I wanted to…

    And another question on this line – Is B12 in well water destroyed by boiling or freezing?

    Thank you so much for answering these questions as you find the time to do so.

  • DrDons

    Hi Bea, Since B12 is made by bacteria it can be found in well water. Vitamin B12 is adversely affected by factors such as acidity, heat, as well as certain minerals such as iron and copper. Freezing shouldn’t be a problem. Since it doesn’t appear that we can overdose on B12 I would continue taking your supplemental B12 as the problems with deficiency can be severe and irreversible. I would follow Dr. Greger’s recommendations for insuring adequate B12 intake either by taking 2000 mcg once a week, 100 mcg daily, or at least 2 servings daily(at least 6 hours apart) of B12 fortified foods each containing at least 20% “Daily Value” on label. It is also advisable to periodically check the safety of well water (the EPA recommends annual checks).

  • Thanks for the reply – Yes, I’ll continue on just as before under Dr. Greger’s advice. Feel great so far – It must be working. ;)

  • Michael Greger M.D.

    Also be sure to check out my associated blog post Vegan B12 deficiency: putting it into perspective!

  • Phil

    First off, great and informative site. I did enjoy your “Maximum Nutrition”!
    I read alot about the B12-Issue. Since I went vegan about 4 weeks ago; how pressing is this matter? When does B12-insufficiency start to show up? Should I already be worried? Doesn’t my Marmite (UK)/Vegemite (AUS) cover my B12 needs?

    Or, blatantly, if B12 is a bacterial vitamin coming from the soil, why bother wash organic, homegrown vegetables?


  • Farseer Nobundo

    Is b12 replenished in the body if you ingest it say once per month in high dose? For example I am vegan most of the time, but once per month I eat liver (which contains a lots of b12)?

  • marta

    I have just spoken to my doctor, a hematologist. He told me that -here for sure, Warsaw, Poland- B12 shortage is hardly ever an issue. He has many vege patients suffering with enamia- women mainly, he says- but the problem is tha lack of iron, not B12. Btw, B12 is found in inactive yeast, is this a good supplement?

  • Brean

    Unable to hear the volume and I have excellent hearing.

  • Do tempeh or natto or miso or fermented vegetables contain B12? Is it produced by the fermentation process?

    • Thea

      Harriet Sugar Miller: I don’t know if those foods contain B12 or not, but I do know that B12 is a by-product of bacteria.

      From the above article: “It’s true, plants don’t make B12. Animals don’t make it either. B12 is made by microbes that blanket the earth. These bacteria grow in the guts of animals, which is why their bodies and products can be a source of this vitamin. Our herbivore primate cousins get all they need ingesting bugs, dirt, and feces, and we may once have gotten all we needed by drinking out of mountain streams or well water. But now we chlorinate our water supply to kill off any bugs. So we don’t get a lot of B12 in our water anymore, but we don’t get a lot of cholera either—that’s a good thing.”

      I also understand that we can’t count on foods that may naturally contain some B12 to have enough of it to meet our needs. Thus, the safest way to make sure we have enough B12 is to take a supplement.

  • Biljana

    Hello, i wonder does sauerkraut contain B12? Thank you.