View Full Version : Does anyone need 1000 mcg B12/day from supplements?

Apr 21st, 2011, 03:27 PM
I've never seen a single dietician, scientist or doctor recommend as much as 1000 mcg B12 supplementation per day on a regular basis (with one exception: a dietician who also happened to have an online store selling bottles of 1000 mcg B12 supplements). Such high amounts are only needed in special situations - like when someone has an acute B12 deficiency, or have an absorption problem meaning that the only way to absorb B12 orally is through so called 'passive diffusion' - which has a very low absorption rate, meaning that you need a very high B12 intake to achieve normal B12 absorption.

Meat eaters often consume more B12 than they need, and just to illustrate how much 1000 mcg B12 actually is:

In order to consume 1000 mcg B12 from sources that are common for non-vegans, one would have to eat eg.:

Pork: 8 lb (3,8 kg)
Ham: 525 lb (238,1 kg)
Mutton: 50 lb (22,5 kg)
Sardines: 25 lb (11,2 kg)
Shrimps: 118 lb (53,5 kg)
Cow’s milk (not boiled): 170 lb (76,9 kg), or 200-250 glasses of milk
Beef: 52 lb/23,6 kg

.... or hundreds (if not thousands) of chicken eggs.

There are a few more aspects to consider here.
"The bioavailability of physiological levels of vitamin B12 from food is
therefore limited by the capacity of the IF-mediated mechanism to ~1.5-2 g/meal. This mechanism takes a few hours to recover and can then mediate the absorption of a similar amount as a subsequent event. Link (http://www.food.gov.uk/multimedia/pdfs/EVM0020P.pdf)) (Also discussed here (http://www.veganforum.com/forums/showthread.php?2721-Food-for-thought-At-what-levels-is-B12-absorption-best).) So - whether someone gets B12 from food or from supplements, they won't see any linear increase in B12 absorption from consuming more B12. Eating twice as much 'something' which contain B12 does not mean getting twice as much B12. According to the food.gov.uk source, absorption per meal flattens out at around 2 mcg. This means that the few meat eaters who consume, say, 3-4 times as much B12 from meat etc., as the average omnivore don't absorb 3-4 times as much B12.

So - if an omnivore spreads his need for 1000 mcg B12 from his diet over multiple meals, he will absorb more than if he consumes all this food in one meal. According to the UK government source, he may get as much as 2 mcg pr meal, or eg. 8 mcg/day if he for instance eats 500 eggs for breakfast, 2 lb pork for lunch, 12,5 lb mutton for dinner and 29,5 lb shrimps just before going to bed.

But only circa 30% of the B12 he got from his 500 eggs for breakfast is absorbed, due to the known B12 absorption limitation in eggs. Too bad. He needs to set the alarm clock to wake him up in the middle of the night (he needs a few hours between the meals to recover his ability to absorb B12, right...), and have, say, 7.5 lb sardines.

Even if he actually would be able to consume 1000 mcg B12 in a day, he could absorb only circa 8 mcg, following the above suggested diet. But it is generally thought that 5-30% of the B12 found in the omnivorous diet are inactive molecules. An average of 5 and 30 is 17.5%. It is also often mentioned that those inactive B12 analogues may block the absorption of real, active B12 (this is a huge topic, but let's keep it simple for now....). So if he consumes 8 mcg B12, circa 1.4 mcg of these 8 mcg are probably inactive B12 analogues. That's 6.6 mcg left. But the 1.4 mcg inactive B12 analogues may also, in worst case, block for 1.4 mcg of the active B12. That's 5.2 mcg active B12 left.

1000 mcg B12 is a lot of B12. But people with B12 deficiency do need a lot of B12. However, it's often easier to absorb B12 from supplements than from food (this has to do with how B12 in food needs to be 'released' from it's source in order to be absorbed), so 1000 mcg B12 from a supplement should be more efficient that living on the shrimp/sardines/pork/eggs/mutton diet, and clearly be more enjoyable.

One well known theory is that when consuming more than circa 10 mcg in one meal/tablet, we can absorb only circa 0.5% of the B12 we consume. That would mean around 5 mcg per 1000 mcg table, or circa 10 mcg B12 from a 2000mcg tablet.

Here's what Vegan Society says, on this (http://www.vegansociety.com/lifestyle/nutrition/) page:

Vitamin B12: Readily available in fortified foods such as yeast extract, soya milk, breakfast cereal and margarine. Alternatively a supplement can be provided. Daily amount: 3 micrograms.
And on this (http://www.vegansociety.com/lifestyle/nutrition/b12.aspx) page:

Most vegans consume enough B12 to avoid anaemia and nervous system damage, but many do not get enough to minimise potential risk of heart disease or pregnancy complications.

To get the full benefit of a vegan diet, vegans should do one of the following:

•eat fortified foods two or three times a day to get at least three micrograms (μg or mcg) of B12 a day or
•take one B12 supplement daily providing at least 10 micrograms or
•take a weekly B12 supplement providing at least 2000 micrograms.

If relying on fortified foods check the labels carefully to make sure you are getting enough B12. For example, if a fortified plant milk contains 1 microgram of B12 per serving then consuming three servings a day will provide adequate vitamin B12. Others may find the use of B12 supplements more convenient and economical.

These numbers are based on the theory that we need more than what WHO, most governments etc think we do.

But whether we need 2.4, 6 or 10 mcg per day.... there are nobody out there who claims to have scientific evidence for saying that humans - vegan or not - need to consume 1000 mcg B12 daily.

The unfortunate existence of the many 'B12 killers' out there may suggest that most humans need more B12 than they think they do, but until there's at least some scientific evidence that we need a lot more B12 than current, general recommendations, it's IMHO not a good idea to start to take 150-200 times the recommended B12 amounts on a daily basis. The idea that vegans regularly should need to consume B12 amounts equivalent to eg. 53 kgs shrimps or 22.5 kgs mutton sticks out as a rather bizarre idea to me.

If you come across anyone who claims that we need this much B12 daily, please ask why - and ask where they have this information from, and - most of all - ask why they think we need to consume a lot more B12 than it's possible to get from omnivorous food.

Apr 23rd, 2011, 01:03 AM
This is great information here!.. i too have had a nutritionist recommend 1000 mcg daily, but like you said he was an owner of a shop that sells it. I used to take between 100-250 mcg a day, and felt fine, then I started doing the 1000 mcg and started to not feel well from it so I stopped taking it altogether...at the higher doses it started making me really drowsy and achy and just generally not feel well. I read that whole thread about too much B12. When I start it again I'll do small amounts of it. What amazes me is that i always see multivitamins with 18 mcg or so, but if you just want to buy the b12 on its own, they only make huge amounts. What I had been hearing was that supposedly you needed to take all 1000 mcg in order to absorb the 3 mcg or so that you needed a day.. I'm thinking that may not be true though because i did notice positive effects from only 100 mcg a day. And then why would all the multi's have smalll amounts of b12...

Thanks for posting this!!!

Apr 23rd, 2011, 10:24 AM
What I had been hearing was that supposedly you needed to take all 1000 mcg in order to absorb the 3 mcg or so that you needed a day...
If a nutritionist recommends 1000 mcg daily based on having seen someone's blood test, it could mean that s/he suggested a therapeutic amount for a B12 deficiency. Or s/he could suggest 1000 mcg because - based on studies focusing on short term, allergic reactions - many believe that it's safe to such a high amount of B12 daily, for years, without any health risks involved. But where are the studies on eg. cancer risk in humans who have taken 1000 mcg daily for years? I haven't seen them.

And again: even if you take 100 mcg/day, you have a more than 10 times as high B12 intake as the average meat eater has.

Some of the confusion arises from the known fact that we don't absorb all the B12 we consume, but I have a feeling that some recommended amounts are based on compensating for this more than once, or the theory that reducing homocysteine amounts as such reliably will reduce the heart disease risk. By "compensating for this more than once", I mean that the common recommendation 1.5mcg-2.4mcg (or up to 6mcg) B12 intake/day already should take the problem with not-all-consumed-B12-is-being-absorbed into consideration. They don't suggest that we need to absorb 1.5 or 2.4 mcg B12 per day, but to consume it. Most eaters generally consume more B12 than humans need, and they consume around 5 mcg/day (but spread over multiple meals).

The reason The Vegan Society (http://www.vegansociety.com/lifestyle/nutrition/b12.aspx) recommends as much as one 10 mcg tablet daily isn't that they think we need to absorb 10 mcg B12/day either. It's more convenient to take on pill/day than to take 3 a day. They write: "The US recommended intake is 2.4 micrograms a day for ordinary adults rising to 2.8 micrograms for nursing mothers. The German recommendation is 3 micrograms a day."

TVS continues: "Recommended intakes are usually based on 50% absorption, as this is typical for small amounts from foods."
If an omnivore eats/drinks something which (in total) contains 1 mcg for breakfast, he'll never absorb as much as 1 mcg B12.

Furthermore, "To meet the US and German recommendations you need to obtain sufficient B12 to absorb 1.5 micrograms per day on average." According to a table in Vegan Society's book on nutrition, one needs an intake of around 7 mcg B12 to absorb 1.5 mcg B12.

Dr. Herbert suggested, in 1987, that the minimum daily requirement for B12 (for 'normal people') appears to be 0.2-0.25 micrograms per day absorbed from food (Herbert V. 1987. Recommended dietary intakes (RDI) of vitamin B-12 in humans), and that what we need to "sustain normality" is probably within the range of ~0.1 mcg. A main reason why an absorption of around ten times these amounts are commonly recommended today is probably that we now know how coffee, contraceptive pills, sugar and much more affects our B12 status. Another reason may be the knowledge about the up to 30% inactive B12 analogues in 'normal', omnivorous diet.

Most likely, taking half a (non-multivitamin) B12 tablet containing 2.5 to 3 mcg twice a day would meet the requirements of healthy humans not getting any B12 from food - but then again, I'm not a big fan of general recommendations or B12 recommendations which don't take exposure to 'B12 killers' into consideration.


If we stick to absorption needs, and not consumption needs - let's stick to assuming, at least for now, that we need to absorb 1.5 mcg B12/day. According to http://ods.od.nih.gov/factsheets/vitaminb12/:

"Thus, oral doses deliver much less cobalamin per dose once IF capacity (1-2 μg) is exceeded in normal persons or is absent in PA (Table 1). Because of wide individual variations, 1000 μg must be taken daily if malabsorption exists. Oral cobalamin is also less effectively absorbed after a meal than when fasted (1.8-7.5 vs 2.8-13.4 μg of a 500-μg dose). Small doses (5-10 μg) are thought effective in cobalamin-deficient patients with normal Schilling test results."

In other words:
500 mcg, taken after a meal: an average of 4.65 mcg absorbed.
500 mcg, taken when fasted: an average of 8.1 mcg B12 absorbed.

They also write "Data from the 19992000 NHANES indicate that the median daily intake of vitamin B12 for the U.S. population is 3.4 mcg".

In both cases - based on these sources - more than three times the B12 we need to absorb pr day (using the 1.5 mcg reference) is absorbed. Other references suggest that (just over) 5 mcg B12 is absorbed when taking 1000 mcg.

An interesting aspect of all this is that B12 is best absorbed in much smaller amounts than the amounts found in animal products, where an estimated average of 50% of the B12 eaten is never absorbed. The more microscopic amounts B12 amounts we consume per meal (much lower than found in milk, cheese and burgers), the closer to 100% the absorption rate comes.

One source writes "Absorption of B12 varies from about 50%, if about 1 microgram or less is consumed, to about 0.5% for doses of 1000 micrograms (1 milligram) or above", but at around 0.2 mcg B12, pretty much all the B12 is absorbed. With 4 meals a day, that's around 0.8 mcg B12 absorbed, and with some water (which once wasn't as 'denaturalized' as it is today) between the meals we should, back in the day, have reached the daily needs without a problem, without any use of animal products.

More than that, we wouldn't have all the 'B12 enemies' we have today - or at least, we could easily avoid those which existed (like sugar and coffee), so I'm almost 100% certain that we would exceed our B12 needs, but by safe margins, and without problems associated with diets very rich in B12. These diets don't not only contain more B12 than we need, but also much more B12 per meal than the human body can absorb (per meal). These diets simply don't qualify as a smart reference.

IMHO it's important *not* to glorify the B12 levels in a meat based diet as ideal for all humans. But: If we assume that we need to absorb as much as 1.5 mcg B12 pr day, around 7-10 mcg B12 needs to be eaten if taken in one portion. One daily 9 mcg pill taken by a vegan would mean that he would reach the average B12 absorption of a meat eater (if we assume that the meat eater consumes circa 5 mcg B12 spread over several meals).

Personally, I think it's better to reduce the B12 absorption (compared with omnivores' B12 absorption) and at the same time reduce our exposure to all the B12 killers out there, which usually are unhealthy for a number of non-B12 related reasons as well. We aren't striving to become a part of the cancer statistics.

A glass of cow's milk provides circa 0.9 mcg, but only 0.6 mcg is absorbed, and if two glasses of milk is taken, there's still less than 1 mcg absorbed. A double cheeseburger may contain as much as 30% of what a human need to consume every day, but still - only one mcg (or less) is absorbed from eating it. These numbers should put some perspective on the 'need' for 1000 mcg pills daily. And by the way - if someone consumes eg. milk with that burger (or with a cheese or tuna sandwich) the absorption rate goes down for each of these components. Here's why: human bellies don't know the whether the B12 molecules which ends up in it comes from milk, cheese or fish - the max. capability of B12 absorption is per meal, including everything we eat and drink. (Consuming very high levels of liver may be an exception.)

The same is of course true for plants that may contain B12. White button mushrooms were in 2009 reported to contain B12 which has a "retention time and mass spectra identical to those of the standard vitamin B(12) and those of food products including beef, beef liver, salmon, egg, and milk but not of the pseudovitamin B(12), an inactive corrinoid in humans". The B12 activity in mushrooms may be better or worse than eg.in eggs, but mushrooms are really light weight and nothing someone would consume high amounts of every day... The same is true for other plants reported to contain bioavailable B12. Eating double or quadruple portions of nori, chlorella or sea buckthorn won't provide double or quadruple B12 amounts.

All these different types of reference values (RDA, RDI, DRI, DV, EAR, DRV, AI... ) used in B12 (and other) recommendations also add confusion to all this, but it's not *that* difficult: Anyone who doesn't get (enough) B12 from his/her diet should take some B12 supplementation, but not overdo it, and try to avoid B12 killers. Taking proper blood tests is also a good idea.

B12 needs calcium for absorption, calcium needs vitamin D for absorption, and sunlight is our main vit. D provider. So I'll finally stop typing about B12 (for now... :-) ) and get out in the sun!

Apr 23rd, 2011, 01:02 PM
I'm with the others that 1000 mcg doesn't sound like a good recommendation. As an omni I didn't eat alot of meat to begin with, some days none at all. I did take a daily vitamin supplement containing 12mcg (200% RDA) of B12 and my blood test in February came back with no issues or vitamin deficiencies. So I speculate most omni's aren't even getting nearly that amount--they don't even think about it I bet.

Feb 11th, 2013, 01:20 AM
I have tried various different b12 tablets,1000ug,500ug and have felt negative side effects,
i am now taking a 25ug tablet broke into quarters and still feel like this is too much for my body.

Feb 11th, 2013, 01:22 AM
How do you know it's the b12?

Mar 23rd, 2013, 10:30 PM
Thanks so much for your thread Korn!

I've been 100% vegan since October, 1986. In about 2001, I started having symptoms of B12 deficiency (tingling in hands), and I started taking B12 - the megadose of 1000 mg. Deficiency symptoms went away in about a month. Of course, I've missed some days, but all in all, I've probably averaged around 5000 mg/week for over a decade.

In 2010, I was surprised to find that my LDL was 105, which is in the High range for "bad" cholesterol. I know some people are genetically prone to high cholesterol, but it's not in my family.

I checked again in 2012. My LDL had risen to 128. Total chol. went from 184 to 212 (High). Triglycerides went from 54 to 113.

I had myself checked for hypothyroidism. It's not that.

Our bodies need a certain amount of LDL for cell membranes, synthesis of Vit. D, bile, etc; so we produce our own. But I couldn't figure out why my body was producing so much!

Recently I came across a possible link between B12 and cholesterol synthesis. One of the functions of B12 is to produce Succinyl CoA from Methylmalonyl CoA. Succinyl CoA could stimulate production of endogenous cholesterol.

Specifically, "S-CoA stimulates the enzyme succinyl-CoA-acetoacetate transferase to increase the production of aceto-acetyl-CoA, which can be utilized to form hydromethylglutaryl (HMG)-CoA, and mevalonate-biosynthetic precursors of cholesterol (Norman H. Ertel, MD, FACP)."

I think it's possible that a consistent B12 megadose could (possibly) lead to overproduction of endogenous cholesterol.

Anyway, it's something to think about. I'll be testing again in about 3 months. If my cholesterol is lower, well then.....I'll report back sometime in August. Until then, I'm taking a break from B12, but plan to resume later with a much lower dose.

Mar 27th, 2013, 08:29 AM
I've probably averaged around 5000 mg/week for over a decade.
That's a lot of B12!
Have you seen this (http://www.veganforum.com/forums/showthread.php?169-B12-overdose-megadose) thread? Maybe it would be interesting for you to have a look at it, it contains many references to experiences people have with B12 overdosing/megadosing.

Mar 29th, 2013, 08:16 AM
Thanks Korn for the link! I read some of the references. I have to wonder what was I thinking?! I guess I was too lazy to split up the tablet, and I believed what I'd read about there being no side effects. I won't be taking any B12 for at least a couple of months, and then I'm going to have my cholesterol tested again. I will be so happy if it goes down! I found some B12 drops with only 25 ug per drop. I may try one/week of those later.

Another possible side effect from the B12 might be the contact dermatitis that mysteriously appeared several years ago. If that goes away too, I will be stoked!

May 24th, 2013, 02:54 AM
My cholesterol already dropped after discontinuing the B12 megadoses!

I thought I should get a baseline for where my cholesterol is now and then get tested again in August. So last week, I visited my ND and discussed my cholesterol theory with her and got a lab script. The results show that my cholesterol is already down from last year, although I haven't done anything different except that I stopped taking the B12 since about March 23 (date of my first post above).

I was very pleasantly surprised to see that not only did my LDL and total cholesterol drop by several points, but also my triglicerides dropped considerably, and my HDL went up!


Total cholesterol 2012: 212 H
Total Cholesterol 2013: 194

LDL 2012: 128 H
LDL 2013: 111 H

Triglycerides 2012: 113
Triglycerides 2013: 53

HDL Cholesterol 2012: 61
HDL cholesterol 2013: 72

CHOL/HDL ratio 2012: 3.48
CHOL/HDL ratio 2013: 2.69

Cholesterol Non-HDL 2012: 151
Cholesterol Non-HDL 2013: 122

So that's it! I knew there had to be something going on besides heredity (as I'd been told by my MD)! I've been strict vegan since October 1986 for heaven's sake!

I'm still above the normal range for LDL, but I feel pretty confident in predicting I'll be back in the normal range by my next test in August.

In my opinion, Korn is certainly correct to have expressed his concerns on this forum. Thanks Korn!

May 24th, 2013, 10:52 AM
Wow Allyoop, that is really interesting! So glad you shared that cutting back on B12 helped.

I have B complex sublingual drops and the B12 dose in it is 1200 mcg, but I only take it once a week. I used to take it two times a week but was having strange dizzy spells and tingling in hands but cutting back seemed to have helped. I wonder if even once a week is too much though. I have trouble with pills of anything so always try to find alternative routes, but all the sublingual B12s seem high. But maybe it is an absorption issue? I would think you would need less sublingually because most of it goes straight to the bloodstream and bypasses the liver. This is the way it is with my hrt (I had my ovaries out and have osteoporosis hence why I take estradiol). I use a patch and my dose is very small compared to when I tried pills and the dose was much greater.

May 24th, 2013, 09:42 PM
Hi Robinwomb,

Thanks for your reply!

Like you, I'm somewhat perplexed about where to go from here (for dosage). I read my old B12 bottle that contains losenges with 1000mcg B12/ea. Recommended useage is 1 losenge per day. This is just a little less than what you are getting with the sublingual drops. So is there an expected absorption issue with all forms of supplement, and is that why the recommended dosage is so high?

Another possibilitity: the manufacturers may presume that all (or most) of their consumers have their own absorption problem or they wouldn't be taking the supplement! After all, most people with B12 deficiencies are meat eaters with an absorption problem. Therefore, the dose is extremely high. My product says "Suitable for Vegans" on the label, but maybe the manufacturers don't take into consideration that vegans most likely do not have absorption problems.

I thought I'd found a product that provides only 25 mcg per drop, as I posted previously above. But I'd read the label incorrectly. It actually says 25 drops make up one recommended dose of 1000 mcg. So that's 40 mcg per drop. That's still too much for a daily dose, considering that Mayo Clinic advises 2.4 mcg per day. Maybe 1 drop per week would be good if we consider that some of it won't be absorbed. Anyway, it's certainly safer than 1000 mcg per day, in my opinion! Maybe at some point I'll take the 40mcg/week for a year and then have my homocysteine level tested. We long-term vegans are treading on all-new terrain here I think, so it may take some experimenting to get it right.

Jul 4th, 2013, 06:19 PM
Sorry for the delayed reply
Well, iv'e tried all types of b12 from smaller doses (10mcg) to the larger (1000mcg) both cynacobalamin and the methyl form.
with the larger doses if i havent taken any b12 in a while i will feel a big energy rush, but if i continue to take it everyday i will feel tired, unmotivated,dizzy and anxious. With the smaller doses for the first week i will feel fine and then begin to experience the symptoms i did with the larger doses. after this i then stopped for a while and got a b12 reading of around 450.
I have been taking nutritional yeast and the odd low dose of b12 since and i have developed symptoms of a deficency including phychosis which i have never experienced before.
I got a another b12 reading in early june and it was 299, so i may have a problem absorbing the b12. I recently got a b12 oral spray which contains 300mcg of methyl b12 per spray and have been using everyday for the past 2 weeks and am now going to be using it once per week as i was just starting to get the tired symptoms as i did before, but the nerve symptoms are getting better and the phychosis is clearing