The Best Source of Vitamin B12: Supplements, Shots, or Fortified Foods?

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Is it true we can actually absorb some B12 from our own microbiome?

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

To treat vitamin B12 deficiency, intramuscular injections, oral pills, or sublingual lozenges can similarly effectively increase the level of vitamin B12 at sufficient doses, but this is based on blood level targets rather than assessing clinical outcomes, in terms of symptom improvement. So, some believe that at least initially, injected B12 should be the first-choice treatment for patients with severe B12 deficiency––though even with the best treatment, neurological symptoms may take several months or even years to resolve, and may never get better. So, it’s better to prevent deficiency in the first place.

B12 isn’t made by plants or animals, but rather by bacteria, so feces are a good source of vitamin B12. That’s one of the ways our fellow great apes like gorillas get B12. Evidently, dining on dung was seen to be more common after wet weather though, leading to the suggestion that besides its nutritional importance, it may be just that they want something warm to nibble on at the end of a long, cold rain. Thankfully, since the advent of modern sanitation, bacteria and feces are (happily) no longer reliable sources of vitamin B12 for humans.

A large proportion of the bacteria in our gut do make B12 though, but it’s always been thought to be produced too far down to be absorbed. How do we know? Because if radioactively-labeled B12 is squirted into people’s rectums, they don’t really seem to absorb it. But the human colon is about five feet long (1.5 m), and it was just squirted in about a foot (30 cm). What about higher up?

No B12 uptake from the human colon had ever been previously described or considered … until now. B12 was squirted via colonoscopy all the way up to the beginning of the colon, and…dun dun dun DUN…B12 is absorbed in the human colon. Or at least a little bit was. Now the squirt occurred just a few inches (5 cm) from the end of the small intestine, so some of it may have slipped out and was absorbed there, even higher up, but presumably the same could happen with any B12 made by our own microbiome.

The researchers suggest that this potential colonic absorption might help explain an apparent paradox. There are hundreds of millions of vegetarians in India, so why don’t we see more B12 deficiency? Well, vitamin B12 deficiency is endemic in India, with B12 deficiency rates running as high as 50 to 77%. But maybe the reason it’s not closer to 100% is because they’re absorbing a bit from their microbiome. Obviously, though, it’s not something we can count on.

The safest way to prevent B12 deficiency in plant-based diets is to take an oral B12 supplement. B12-fortified foods, like certain brands of nutritional yeast or soymilk, are another option, but they may only provide adequate vitamin B12 when consumed multiple times a day.

What about chlorella and spirulina, which both claim to contain B12? But actually, up to 90% of so-called B12 is pseudo-B12––B12 analogs that look like B12, but are actually unusable by our body. It’s outrageous that manufacturers would advertise real B12 when there may be none. It is crucial that consumers are not misled by wrong information.

What about duckweed, which also claims to have B12? Sometimes it does, but not because it or any plant makes it, but because of variable amounts of bacterial contamination. If you actually disinfect the plants to reduce the bacteria loads in duckweed, you end up with little B12.

It’s the same with seaweed like nori—sometimes it’s contaminated with B12-producing microbes, other times not, and sometimes it has pseudo-B12-producing bugs. For example, in this study, eating nori actually made B12 status worse, whereas in this study nori made B12 status mostly better. But even then, it made B12 status worse in two of the participants.

That’s why those eating unfortified plant-based diets must take B12 supplements. But which kind is best? When researchers asked ChatGPT, it said methylcobalamin and adenosylcobalamin are better than cyanocobalamin, but ChatGPT was wrong. (It must have just sucked up that slimy supplement company propaganda.) Check out my video on why cyanocobalamin is best for most people.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

To treat vitamin B12 deficiency, intramuscular injections, oral pills, or sublingual lozenges can similarly effectively increase the level of vitamin B12 at sufficient doses, but this is based on blood level targets rather than assessing clinical outcomes, in terms of symptom improvement. So, some believe that at least initially, injected B12 should be the first-choice treatment for patients with severe B12 deficiency––though even with the best treatment, neurological symptoms may take several months or even years to resolve, and may never get better. So, it’s better to prevent deficiency in the first place.

B12 isn’t made by plants or animals, but rather by bacteria, so feces are a good source of vitamin B12. That’s one of the ways our fellow great apes like gorillas get B12. Evidently, dining on dung was seen to be more common after wet weather though, leading to the suggestion that besides its nutritional importance, it may be just that they want something warm to nibble on at the end of a long, cold rain. Thankfully, since the advent of modern sanitation, bacteria and feces are (happily) no longer reliable sources of vitamin B12 for humans.

A large proportion of the bacteria in our gut do make B12 though, but it’s always been thought to be produced too far down to be absorbed. How do we know? Because if radioactively-labeled B12 is squirted into people’s rectums, they don’t really seem to absorb it. But the human colon is about five feet long (1.5 m), and it was just squirted in about a foot (30 cm). What about higher up?

No B12 uptake from the human colon had ever been previously described or considered … until now. B12 was squirted via colonoscopy all the way up to the beginning of the colon, and…dun dun dun DUN…B12 is absorbed in the human colon. Or at least a little bit was. Now the squirt occurred just a few inches (5 cm) from the end of the small intestine, so some of it may have slipped out and was absorbed there, even higher up, but presumably the same could happen with any B12 made by our own microbiome.

The researchers suggest that this potential colonic absorption might help explain an apparent paradox. There are hundreds of millions of vegetarians in India, so why don’t we see more B12 deficiency? Well, vitamin B12 deficiency is endemic in India, with B12 deficiency rates running as high as 50 to 77%. But maybe the reason it’s not closer to 100% is because they’re absorbing a bit from their microbiome. Obviously, though, it’s not something we can count on.

The safest way to prevent B12 deficiency in plant-based diets is to take an oral B12 supplement. B12-fortified foods, like certain brands of nutritional yeast or soymilk, are another option, but they may only provide adequate vitamin B12 when consumed multiple times a day.

What about chlorella and spirulina, which both claim to contain B12? But actually, up to 90% of so-called B12 is pseudo-B12––B12 analogs that look like B12, but are actually unusable by our body. It’s outrageous that manufacturers would advertise real B12 when there may be none. It is crucial that consumers are not misled by wrong information.

What about duckweed, which also claims to have B12? Sometimes it does, but not because it or any plant makes it, but because of variable amounts of bacterial contamination. If you actually disinfect the plants to reduce the bacteria loads in duckweed, you end up with little B12.

It’s the same with seaweed like nori—sometimes it’s contaminated with B12-producing microbes, other times not, and sometimes it has pseudo-B12-producing bugs. For example, in this study, eating nori actually made B12 status worse, whereas in this study nori made B12 status mostly better. But even then, it made B12 status worse in two of the participants.

That’s why those eating unfortified plant-based diets must take B12 supplements. But which kind is best? When researchers asked ChatGPT, it said methylcobalamin and adenosylcobalamin are better than cyanocobalamin, but ChatGPT was wrong. (It must have just sucked up that slimy supplement company propaganda.) Check out my video on why cyanocobalamin is best for most people.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Doctor's Note

This is the third video in a five-part series on vitamin B12. If you missed the previous two, check out How Long Does It Take to Become Vitamin B12-Deficient and What Are the Symptoms? and The Best Way to Test for Vitamin B12 Deficiency. Stay tuned for How Much Vitamin B12 Do We Need Each Day? and Are Large Weekly Doses of Vitamin B12 Safe?.

For more on vitamin B12, check out the topic page.

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