How much B12 is there in plant based diet?

[Korn]

How much B12 is there in a plant based diet? Many will claim 'none'. A few will claim that you will get enough.

It all depends on what kind of vegan diet you eat and lots of other factors. From time to other I come across sites that have analyzed the diet of vegans, and somehow claim to know how much B12 their diet contains. Here is a page (from PubMed) stating that the vegan in question would get 1.2 mcg B12/day 'at most':

"Nutritional vitamin-B12 deficiency. Possible contributory role of subtle vitamin-B12 malabsorption.

Carmel R.

Dietary deficiency of vitamin B-12 has been reported, yet most people ingesting vitamin-B12-deficient diets even for many years appear to achieve a balance that does not lead to overt signs and symptoms of deficiency. I present the case of a vegan of 25 years' duration who developed severe neurologic abnormalities due to vitamin-B12 deficiency. His diet provided 1.2 microgram of vitamin B12 daily at most. Despite normal Schilling test findings, he absorbed subnormal amounts of vitamin B12 given with ovalbumin. This poor absorption appeared to be related to his gastritis, achlorhydria, and subnormal intrinsic-factor secretion. Probably, vitamin-B12 deficiency in this patient resulted from both dietary restriction and the subtle malabsorption, neither of which would have sufficed alone to produce the clinical problem. Possibly such malabsorption may also be present in many of those vegans developing overt vitamin-B12 deficiency in whom Schilling test findings have been normal."



This article, also from PubMed, is about a study of the diet of six middle-aged vegans. It concludes that their diet contained 0.3-0.4 microgram vitamin B12/day:

"The vegan diet was rich in folic acid (301 versus 90 micrograms/1000 kcal in MD) but the intake of vitamin B12 was only 0.3 to 0.4 microgram/day (mixed diet: 3 to 4 micrograms/day). No clinical signs of nutritional deficiency were observed in the vegans. Serum protein levels of the vegans as well as their serum lipoproteins were near the lower range of the reference group. In addition, none of the vegans was overweight and their blood pressures were low for their age."

If you find other sites that contains info about daily B12 amounts in vegan food, please post them in this thread!

[wuggy]

I found out recently that I suffer from B12 deficiency which made me edgy, sleepless and moody, also, my eyes were sore. I think some people just don't absorb some vitamins as efficiently as others. I am taking a vegan B12 supplement, and trying to eat sensibly, but more information would be great. When I was pregenant, my iron levels were continually tested and my midwife and doctor were amazed at how high they were (not entirely relevant, but just thought I would mention it!).

[Korn]

From http://www.textfiles.com/food/b12.txt

Some recent dietary intake studies of vegans showed them to be
consuming, (including B12 from fortified foods like certain soya
milks and margarines) an average intake of 1.2 -1.8 micrograms
(Carlson et al., 1985; Sanders et al., 1987; Rana et. al.). In a
Swedish study where fortified foods were not used, the average
intake of .35 micrograms was recorded (Abdulla et al., 1981).
Gill Langely (1988), in his fine survey of the research on vegan
nutrition, reports a study indicating British vegan pre-school
children had a mean intake of 280% of the British RDA (but 5 did
have intakes less than the recommended intake (Sanders, 1981).
An U.S. vegan community that used supplemented soya milk and
yeast, had mean intakes of 15 micrograms or about 660% of US RDA
for children. In none of the above groups were any clinical
signs of deficiency found.

[Korn]

More from the same (not very new) source:

Haematological measurements (Sanders it al, 1978) of 34
vegans who had been on the diet for between one and 30 years
revealed a range of serum B12 levels from 94-675pg/ml -- all
ABOVE the value of 80pg/ml at which deficiency symptoms can
be expected. The majority of subjects took B12 tablets or
food fortified with the vitamin, and those who did had higher
amounts in their blood. THE SERUM LEVELS OF THREE SUBJECTS
WHO HAD BEEN VEGAN FOR 6-13 YEARS (LONG ENOUGH THEORETICALLY
TO EXHAUST LIVER STORES OF B12) WITH NO OBVIOUS DIETARY
SOURCE OF B12 WERE ALSO ADEQUATE, at 120-230pg/ml. All the
vegans were healthy, none showed symptoms of B12 deficiency
and all had normal haemoglobin values. The same report lists
other surveys of vegans which have failed to show symptoms of
dietary deficiency of B12. [emphasis his]

[Korn]

According to a study referred to at this site, "Vegan diets contain very low levels of vitamin B12, resulting in intakes of probably less than 0.5 mcg/day (Chanarin, 1990)"

[Korn]

Looking at these studies, and trying to create an average based on what they have found, here's what I get:

• From post # 1 above: "1.2 mcg at most".
That's a very vague statement, and I don't know how they got to that number, but if there's any scientific basis for that number at all, all it says a potential maximum intake from vegan food (without additional supplements) - it doesn't say anything about the average intake or what kind of diet this person was living on. (This person had been living on a vegan diet for 25 years without taking supplements, and actually developed severe neurologic abnormalities due to vitamin-B12 deficiency, but the this article from PubMed says that his poor B12 absorption appeared to be related to his "gastritis, achlorhydria, and subnormal intrinsic-factor secretion", and that probably, vitamin-B12 deficiency in this patient resulted from both dietary restriction and the subtle malabsorption, neither of which would have sufficed alone to produce the clinical problem." A study based on one person alone, which also includes assumptions isn't very scientific, so we don't know for sure if These assumptions are right or wrong.
• Also from the study cited in post # 1: 0.3-0.4 mcg.
• From post # 3: 0.35 mcg B12
• From post # 5: less than 0.5 mcg B12. (Less than 0.5 is also vague, and also contains a "probably"...)

(Again: If any of you have seen other, similar studies, please post them here!)

If we ignore the '1.2 mcg at most' and 'probably less than 0.5 mcg' comments, there are only two studies left, which have actually come to the same numbers - one says 0.35 mcg and the other says 0.3-0.4 mcg. I don't know if these people were eating plants known for having no B12 in them at all, or if they were focusing on plants that had been reported to contain B12, we don't know how much raw vs. cooked food they ate, if they drank coffee, were smoking or were taking any medicine or were using contraception pills. Still, none of them showed any signs of B12 deficiency. Now, these numbers may not be translatable to other people, but still - how can all this be possible if plants would contain no B12? How can a plant based meal provide B12 if the plants the meal is made of contain no B12?

There are at least five important things to consider:
1) How much B12 do each of us actually need to actually absorb (note the difference between intake and actual absorption)?
Victor Herbert, who definitely wouldn't manipulate any information to make it appear 'vegan-friendly', thought we needed to absorb from food (0.1-0.25 micrograms per day). He even wrote that 'the minimum daily requirement (MDR) for vitamin B12 to sustain normality is probably in the range of of ~0.1 mcg.'. The average of 0.1 and 0.25 is 0.175 mcg B12.

2)What B12 intake is needed in order to absorb the amount of B12 we need to absorb?
We have a thread about this here: Food for thought: At what levels is B12 absorption best? I have quoted studies there, which state that absorption of B12 is best "at small doses below 0.5 mcg, where about 70% of available B12 is absorbed. As the dose approaches 10 mcg, the amount absorbed flattens off at about 1.5 mcg and only about 0.5% of further increases in dose are absorbed". So - at a dose around 0.5 mcg, 70% of the consumed B12 is absorbed. The percentage is probably higher at doses lower than than 0.5 mcg, but let's ignore that for now... If a vegan diet consist of 0.35 mcg pr. day, and 70% of this B12 is actually absorbed, thats circa 0.25 microgram absorbed B12 pr. day. According to Victor Herbert, we need to absorb max 0.25 mcg B12 pr. day. It's interesting to see that these numbers are identical - but read on...

3) Do plants contain B12?
There are a number of reports confirming that plants contain B12. Extremely few plants have been tested for B12, and almost no studies provide any scientific documentation of the ratio between active B12 and passive B12 analogues in plants. There are various problems involved in measuring B12 in plants and to distinguish between B12 and B12 analogues, ind since most people and researchers eat animal products, there aren't many studies out there - but there are some. It's a long time since people with some real knowledge about B12 believed that no plants contained B12 - the discussion is about the amounts, the reliability of this B12, the B12/B12 analogue ratio and whether a healthy human body can consume a mix of B12 and B12 analogues and distinguish between them or not.

4) If we actually absorp enough active, bio-available B12, will some of that B12 be reduced/destroyed after we have absorbed it? That's quite likely. Chlorinated water, for example, is said to destroy not only good and bad bacteria, but also B12, and chlorine is also used because how effective it is compared with other substances that kill bacteria, because it continues to work after we have absorbed it... Active, bioavailable B12 may or may not exists in the plants you eat, but if you or the plants are exposed to chemicals (in water or other food/drink) that destroys vitamins after you have absorbed them, you wouldn't be really safe as such - even if you both consume and actually absorb bioavailable B12. This applies to non-vegans too.

5) If plants actually contain B12, is the problem then that the B12 found in plants are only passive B12 analogues that have no function? B12 analogues are found in plants, in non-vegan food, in supplements and in B12 fortified food. There are various opinions out there about this topic: some claim that B12 analogues will block the absorption of bioavaliable, active B12, while others claim that a healthy body can distinguish between active, bioavailable B12 and passive B12 analogues. Since multivitamin/mineral supplements containing vitamin B12 also may contain analogues of vitamin B12, eating these pills may not be a good solution if the existence of B12 analogues as such always represent a problem and block the absorption of bioavailable, active B12.


If it's correct that we actually don't need to absorb more than 0.25 mcg pr. day, and that vegan food provides an average of 0.25 mcg B12 pr. day, is there a real problem? My guess is that it is a real problem for some, maybe most vegans, for two and a half reasons....

1) Most people (and most food) are exposed to a lot of stuff that destroys/reduces B12.
2) None of us know exactly how much B12 we may get from food, or to which degree this food has the same levels of B12 that it had when it was harvested, or how many days ago it was harvested - in short, we don't know for sure if it contains the same amount of B12 that the two studies above found.
2.5) The homocysteine discussion, which we have a thread about here:
B12, homocysteine, & heart disease. There has been an ongoing discussion about homocysteine, heart disease and B12/folate for several years, and people don't seem to quite agree in that preventing heart disease by increasing the homocysteine levels (by taking B12/folate supplements) necessarily is a good idea. Most people seem to have been thinking that the solution is simple: higher homocysteine is associated with higher risk for haert disease, se lowering the homocysteine levels means lower heart disease risk - but researchers are still trying to figure out what is the cause and what is the effect. According to the studies cited in an article called B vitamins do not protect hearts, posted on bbc.co.uk a couple of years "Taking B vitamins to ward off heart attacks and stroke does no good and may even be harmful". "Scientists had thought that these drugs might be useful by lowering levels of a blood substance called homocysteine which has been linked heart risk. However, a large study looking at this has found no benefit even though homocysteine went down with these supplement pills."

Now, this study was performed on people who already had a heart disease, and also wasn't a study on vegans, so the most interesting part of the article above is probably the last paragraph: "We are still awaiting the definitive trial that takes people with high blood homocysteine levels, which is the indicator of B vitamin need, gives them B16, B12 and folic acid, and measures the reduction in heart attacks or strokes."