B12 overdose / megadose?

[Pascale]

Are B12 megadoses (like in those b12 lozenges with 1 mg) safe to use for an extended period of time?

[Tigerlily]

I have no idea but I do know that taking a lot of B12 makes me feel very nauseous.

[yasha]

I have no idea but I do know that taking a lot of B12 makes me feel very nauseous.
AHHH! Ok I was going to post a thread about being nauseous, and I wonder if it is because I have been taking b12 supplements and eating foods that contain it.

All evening I have been sick on my stomach with a severe migraine.
Is b12 doing this to me or something else?

[Michael Benis]

AHHH! Ok I was going to post a thread about being nauseous, and I wonder if it is because I have been taking b12 supplements and eating foods that contain it.

All evening I have been sick on my stomach with a severe migraine.
Is b12 doing this to me or something else?

Have you always suffered from migraines?

What dose B12 have you been taking?

There is no need for megadoses unless you need to correct a deficinecy. The more B12 you take the less efficently your body absorbs it.

Cheers

Mike

[Tigerlily]

AHHH! Ok I was going to post a thread about being nauseous, and I wonder if it is because I have been taking b12 supplements and eating foods that contain it.

All evening I have been sick on my stomach with a severe migraine.
Is b12 doing this to me or something else?

I can't even take multi vitamins without breaking them in half. Next time I go vitamin shopping, I'm getting a kiddy formula. :p

[Haniska]

Me too, but I can take them with vinegar pretty good.

[thecatspajamas1]

The B vitamins (as well as C) are water soluble, so if you take too much you will pee it out and so theyre not as toxic as the fat soluble vitamins A,D,E, and K.

[Korn]

The B vitamins (as well as C) are water soluble, so if you take too much you will pee it out and so theyre not as toxic as the fat soluble vitamins A,D,E, and K. Hmm... if all B12 that was 'too much' would be thrown away by the body, how would B12 overdose symptoms actually exist - and how could B12 be stored in the body for years?

[thecatspajamas1]

Hmm... if all B12 that was 'too much' would be thrown away by the body, how would B12 overdose symptoms actually exist - and how could B12 be stored in the body for years?

I've been wondering that too- how it can be stored in the body. But what we've been learning in nutrition class is that its excreted with water, so I thought I should add that.

[zzippffizz]

I've been drinking an effervescent energy drink called Zipfizz everyday for a while now. Usually I only have one. Yesterday, i thought it would be exciting to have 6. ((sometimes I like to perform experiments on myself. don't judge me)) Then I looked at the nutrition information. 1 test tube full has 41,667% RDA of Vit B12 as well as 833% RDA of Vit C and caffeine from guarana seed, L-Taurine, etc. I have since developed a rash on my chest, neck, lower scalp and the sides of my torso under my rib cage. I was in class after consuming the 5th test tube. I felt like I was in a dream, sort of. Not drunk/high, but disconnected, ungrounded. It minimally impeded my mental function. I had no trouble taking tests but wasn't always able to follow what people were saying because I felt tired and awake at the same time. I also experienced a Niacin-like burning on the back of my neck and lower scalp. After the 3rd, it was able to sleep during the night. After the 6th, I was not able to nap. After the 4th, I began to feel sad and somewhat anxious. If I had been by myself, I probably would have cried, but I was at school. My blood pressure felt like it might have been high, but I don't own a pocket blood pressure tester so I can't say if it was for sure. Today I decided to check for information about B12 overdose and found this site, after the rash appeared last night. Sorry it's hard to follow the timeline of when I ingested the different doses, but I didn't feel motivated to type it out. If you're curious about any other side effects, feel free to ask.

[Korn]

1 test tube full has 41,667% RDA of Vit B12


And you took five of these?? Ooops...

In some European countries, more than 9 mcg B12 pr. day is considered medical treatment, and can't be bought without a doctor's prescription, and the amount of B12 you consumed is at least 500 times higher than that. If I were you, I'd stay away from anything containing B12 for a while!

[Korn]

There may ne no reliable, detailed studies on the link between high levels of B12 and cancer yet, but here's a link I came across by accident, more or less related to that topic. Cancer is defined as uncontrolled immature cell division. This URL is about a product called Trimethylaminohydroxybicycloheptane Chloride, or 714X.


Here's what they write about 714X and B12:


714X is a non-toxic treatment which supports the body's natural defense mechanisms. It is compatible with most therapeutic approaches seeking to bolster the biological terrain. These therapies are generally referred to as non-conventional, complimentary, alternative, etc.

Clinical observations have revealed certain exceptions in the case of :
Vitamin B-12
Vitamin E
Shark and bovine cartilage as well as other antiangiogenic products.

These exceptions apply to dietary supplements but do not include vitamins B-12 and E found in food.

Vitamin B12

It is recommended not to simultaneously use 714X and vitamin B12 supplements.

Vitamin B12 accelerates cellular division (especially blood cells) without distinguishing healthy cells from immature cells. There is nothing to be gained by stimulating cell division in an already hyperactive organism. This restriction does not affect vitamin B12's properties in a normal context.

For those persons having had a partial or total removal of the small intestine who wish to take 714X, the above exception concerning vitamin B12 does not apply as this vitamin is essential for such persons' survival.

I think the warning is very vague: First they write that 'It is recommended not to simultaneously use 714X and vitamin B12 supplements' and then that 'there is nothing to be gained by stimulating cell division in an already hyperactive organism'. But the most interesting part is this one: 'Vitamin B12 accelerates cellular division (especially blood cells) without distinguishing healthy cells from immature cells'. I've mentioned warning from doctors against taking B12 for people who have cancer (or are on their way to develop cancer) in a couple of other posts, and this URL confirms that B12 stimulates cell division (cancer= exaggerated cell division), and that B12 isn't able to distinguish between healthy and immature cells.

According to this (http://www.wsws.org/articles/2000/jan2000/canc-j18.shtml) link, reports predict that four in every ten people in Britain will develop cancer at some point in their lives. The article also mention that Britain has one of the worst survival rates for cancer in the developed world, but IF we should apply those numbers on the members of this forum, 1600 of us should develop cancer at some point in our lives. Realistically, such studies (when/if they are correct) tells us that a lot of people are in a situation where they may or may not develop cancer, based on a lot of things they may or may not do something with.

There are only a few studies that confirm a link between cancer and high B12 levels (see earlier posts in this thread), but in spite of not having hundreds of studies suggesting or confirming such a link, eating a too much of a substance that stimulates cell division, but can't distinguish between healthy and other cells doesn't sound like a terrific idea to me.

[Korn]

From http://www.acu-cell.com/nico.html :

Some uninformed practitioners believe that there is no overdose possible with Vitamin B12, however
5-10% of the population presents with above-normal levels of Vit B12, so if injections are erroneously
given, they can trigger a number of adverse symptoms that may include coronary artery spasms with
chest pains, numbness or pain down their right arm, and/or TIA-like symptoms with tingling / numbness
on the right side of the face.
There is also a risk of hypokalemia, pulmonary edema, peripheral vascular thrombosis, optic nerve
atrophy for someone with Leber's disease, and others. Risks from intranasal use of Vitamin B12
include glossitis, headache, sore throat, rhinitis, and feeling of "pins and needles." Individuals suffering
from Mitral Valve Prolapse (MVP) are also vulnerable to experience a worsening, or an acute flare-up
of MVP symptoms following a Vitamin B12 shot if not indicated.

Even without having had any Vitamin B12 injections, individuals who run naturally high Vitamin B12
and cobalt levels (which may include patients with mitral valve prolapse), tend to frequently suffer from
tachycardia, panic-anxiety attacks, or angina-like chest pains, that may be accompanied by numbness
and tingling in the face or extremities.
In contrast to cellular measurements, blood tests for cobalt or Vitamin B12 levels (including the Schilling
test) are not only very unreliable, but at times alarmingly wrong, subjecting patients to improper therapy,
or routinely misdiagnosing them as Psychiatric Cases, when in fact correcting their abnormal cobalt,
Vitamin B12 and nickel status (or ratios) could resolve the problem.

Getting too much B12/cobalt from a vegan diet is NOT a problem, but people who supplements too much with B12 in order to be 'on the safe side' may experience some of the overdose symptoms described above.

[Korn]

From http://www.angelhealingcenter.com/AmalgamProtocol.html :


14. B Complex: Should provide at least 15-25 milligrams of each of the various B vitamins. Take the number of tablets indicated to provide the desired amounts. [NOTE; A word of caution concerning those individuals taking large amounts or injections of vitamin B12. There is limited scientific information indicating that vitamin B12 can methylate mercury. Consequently, during the entire amalgam replacement process, every effort should be made to eliminate excess B12 intake. If you must receive B12 injections, request your physician to use hydroxocobalamin.]

[nervine]

Are B12 megadoses (like in those b12 lozenges with 1 mg) safe to use for an extended period of time?

I just bought a packet of something like that too. It's together with Natrium Chloride. I plan on taking them once or twice a month..

[ella_vega]

hi korn.

very inteesting issue.

i will follow the thread.

[Michael Benis]

Getting too much B12/cobalt from a vegan diet is NOT a problem, but people who supplements too much with B12 in order to be 'on the safe side' may experience some of the overdose symptoms described above.

I'd caution everyone to read Korn's words carefully. What's important is the "too much". The Vegan Society recommends either eating foods containing synthesised B12 or supplementing with it. Supplementation to be on the safe side is responsible for vegans, both for our own health and to be effective advocates for a vegan diet. Taking very high levels of supplements for a long time without supervision/tests is obviously not responsible.

Unfortunately the site cited (:D) by Korn (and it is a commercial site) does not state any of the sources of its information. However it appears that the part about "naturally high levels" is the author's own conclusion as far as I can gather. The studies/papers referred to seem to have been about the inappropriate use of high injected doses of B12.

Please don't use this as a reason not to supplement. Several vegan pioneers suffered greatly from B12 deficiency. There's not excuse for us to waste their efforts.

Cheers

Mike

[Korn]

What's important is the "too much".

Yes, that's important. OTOH, if someone goes vegan today, they may already B12 levels way above the average population, and too high levels of B12 is - according to various sources - associated with health problems. Ohters seem to suggest that one can never get too much B12.


Supplementation to be on the safe side is responsible for vegans.

But then again - you're not necessarily on the safe side if you take supplements. Giving such an advice can create a several false illusions, for example that (if B12 analogues actually is a real problem) that supplements or fortified food always contain bioactive B12 and no B12 analogues, or that everybody who takes supplements can absorb the supplements they take, or that persons who are exposed to more 'B12 killers' (http://veganforum.com/forums/showthread.php?t=196) than the average population is just as 'safe' on x mcg B12 daily as someone who are exposed to an 'average' amount of B12 destroying factors.

We have circa 6000 members here, and if it's correct that 1% of all people (vegans included) have a B12 absorption problem, that alone would mean that 60 of our members could develop severe B12 deficiency based on absorption problems alone (problem that has nothing to do with their vegan diet) - if we would have given advice a la 'take supplements and you're safe'.

There are lots of meat eaters out there, and while we know that lots of them are short in folate, Omega-3 and many other nutrients, between 10 and 40% of them also have low B12 levels. Meat eaters normally consume 'enough' B12, and I won't contribute to all the simplification around B12 that both some vegans and non-vegans do. Your B12 status is about a lot more than how much B12 you consume, and to inform about this is important.

Vegans are obviously concerned with which nutrients that needs special attention for vegans, but if both vegans and non-vegans keep talking about which nutrients vegans need to pay extra attention to, and never inform about the fact that non-vegans also have a lot of nutrients that probably are very low or even deficient in, the information is unbalanced, and will give a wrong picture of the healthiness of living on a plant based diet.


There are vegans who have had too low B2 levels, and based on studies that show that 10-40% of non-vegans have low B12 levels as well, there are between 6 and 24 million people in UK alone with low B12 levels - and most of these (95%?) are not vegans. Of course there are vegans with B12 deficiency, and there should more vegans, percentwise, than non-vegans with B12 deficiency, because vegans have other nutrients they need to pat extra attention to than non-vegans, and B12 is the main think to look out for for vegans. There's reason not to pay attention to B12 levels for vegans, and it doesn't help a B12-deficient vegan much to know that non-vegans are deficient in a number of nutrients (http://veganforum.com/forums/showthread.php?p=368908)...

[Michael Benis]

Korn, sure there are lots of variables, but let's cut to the chase: Are you changing your previous advice and not recommending vegans to take a B12 supplement at the lower (RDA) levels?

[Korn]

Are you changing your previous advice and not recommending vegans to take a B12 supplement at the lower (RDA) levels?


I'm not 100% sure about what you mean by 'take a B12 supplement at the lower (RDA) levels', but (of course) I don't think anyone should have too low levels of anything, and that if they do, they should so something about it.

I'm also saying that...

• Both vegans and non-vegans may need to take supplements. It seems that non-vegans need to worry about more nutrients than vegans, but when it comes to B12 specifically, a vegan is more likely to develop a B12 deficiency than a non-vegan (the opposite is true for other nutrients).

• If you miss a nutrient, taking a pill containing that nutrient may solve the problem - but not always. Due to potential absorption problems and other reasons, there's no such thing as 'take a pill and you're safe' for everybody.

• Getting enough B12 isn't only about your B12 intake, which is why a general advice saying 'take a pill' may be either useful or cause harm, depending on the person who is receiving this advice.

• Just like high levels of folate can 'mask' low levels of B12 (in the sense that a starting B12 deficiency may not be discovered at an early stage), compensating for an unhealthy lifestyle by eating a lot of supplements may also 'mask' the fact that your lifestyle (total food/drink intake - plus lack of sunlight/fresh air and exercise) is the problem, it's not the lack of taking supplements.

• If a person needs to take a nutrient supplement, she needs to remember that the amount she needs to consume varies from person to person. Giving advice that's trying to simplify the situation may complicate the situation.

Example: Some people may think they eat enough plants if they follow the advice about eating '5 a day', but that advice is extremely over-simplified, and may create a false illusion that they're getting the antioxidants, phyto-chemicals, fiber, folate etc. they need. Some people give a similar kind of advice about B12.

• Let's say it's 500,000 vegans in a country, and that 50% of those vegas take B12 supplements. That's 250,000 vegans who don't take a B12 supplement (there may be other people living on a vegan diet as well, like vegetarians with milk allergy or lactose intolerance, but let's ignore them for now). If it's right that 1% of these 250,000 have a B12 absorption problem (which has nothing to do with their vegan diet), that's 2500 vegans in that country who should develop serious B12 deficiency symptoms. Two thousand five hundred! So... the 'I know some long time vegans who had B12 deficiency'-"argument" agaisnt going vegan is totally non-valid, because in any group of this size (vegans or non-vegans), based on the numbers above, there should be 2-3000 people with a serious B12 deficiency anyway within this group, even if half of these people took daily B12 supplements.

• There's no reason to use any of these numbers as an excuse for ignoring the fact that B12 is one of the nutrients that vegans need to pay extra attention to. Unhealthy vegans is bad marketing for veganism, and even if many people eat vegan for health reasons alone, others/vegan newbies may think that vegan food isn't as healthy as non-vegan food. By staying healthy more people will understand that vegan food is healthy.

The median intake of vitamin B12 from food for non-vegans is estimated to ca. 5 mcg/day. (The RDA for B12 is normally around 2.4 mcg). At least one vegan site suggests that vegans should take 10 mcg daily four times the RDA, and twice the average B12 intake for omnivores - even if absorbing B12 from supplements (if taken the 'right' way) may be more efficient than absorbing it from food (due to the difference in the protein binding). This is probably based on the idea that increasing homocysteine levels always is good for your heart, but there is still disagreement about this, and even if it is right that increasing the homocysteine levels always is good for your heart, I'm against any kind of nutrient information that - while it is meant in a helpful and positive way - gives the impression that vegans, unlike non-vegans won't get enough of the nutrients they need and therefore - again, unlike non-vegans - have to take supplements.

When there is disagreements among health professionals about important certain issues, it's better to inform about these disagreements than to decide what you mean, promote your opinion and not mention that there are others who are having opposite views.

I'm happy to continue this discussion (about supplements and what kind of advice that makes sense to give to vegans about B12), but let's do it in another thread, OK? :)

[Korn]

Here are some more links about B12 overdosing:

http://www.iscid.org/encyclopedia/Vitamin_B12:

It is possible to overdose on vitamin B12; negative effects include cardiovascular, dermatologic, gastrointestinal, and hematological problems.

"Nutrition for Vegetarians" by Drs. Agatha and Calvin Trash:

"In animals studies, there have been cases of increased cancer production in animals receiving high levels of B-12. It has been noted that the animals have an increased production of white blood cells such as occurs in chronic myelogenous leukemia. A case has been reported of acute myeloblastic leukemia resulting from B-12 overdose in the treatment of pernicious anemia."

http://www.newswise.com/articles/view/513540/

These days, most health warnings about vitamins focus on the danger of overdose. For vitamin B12, though, it's more likely that people are getting too little. In fact, B12 deficiency is the most common nutritional deficiency in the developing world and possibly in the United States as well.

http://online-vitamin-info.com/vitamin_b12.html

Although very rare, a vitamin B12 overdose can result in some forms of anemia, hyperthyroid condition, tingling or numbness in arm or face, anxiety, panic attacks, insomnia and heart palpitations among other conditions. If you have been taking large quantities and experience these problems, cut back on your intake. Medical treatment should not be required for vitamin B12 overdose if you exercise moderation and common sense.


http://www.essential-vitamin-supplements.com/Vitamin_B12_supplement.html

Here are some of the most common problems or ailments of low vitamin B12 levels:

– Loss of appetite
– Growth deficiencies in children
– Excessive tiredness
– Brain damage
– Neuritis
– Nervousness
– Spinal cord degeneration
– Feelings of depression
– Weakness and dizziness
– Tingling or numbness in the extremities

Vitamin B12 deficiency causes neural tube defects during pregnancy. Vitamin B12 supplement or a vitamin B12 rich diet is highly advisable for adults over 50. Vitamin B12 supplement overdose does not generally pose much of a danger.

http://health.yahoo.com/drug/d00413a1:

What happens if I overdose?

An overdose of cyanocobalamin is unlikely to threaten life. Call your doctor, an emergency room, or a poison control center for advice if you suspect an overdose.

Symptoms of a cyanocobalamin overdose are not known.
...and then, on the same page:

If you experience any of the following serious side effects, stop taking cyanocobalamin and seek emergency medical attention:
an allergic reaction (difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or hives);
chest pain or difficulty breathing; or
unusual warmth, redness, or pain in an arm or leg.
Other less serious side effects may be more likely to occur. Continue to take cyanocobalamin and talk to your doctor if you experience

headache;
upset stomach or diarrhea;
numbness or tingling;
fever;
dizziness;
felling of swelling of entire body; or
itching or rash.
Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

http://ods.od.nih.gov/factsheets/vitaminb12.asp

What is the health risk of too much vitamin B12?

The Institute of Medicine of the National Academies did not establish a UL for this vitamin because vitamin B12 has a very low potential for toxicity. The IOM states that "no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals" [7]. In fact, the IOM recommends that adults older than 50 years get most of their vitamin B12 from vitamin supplements or fortified food because of the high incidence of impaired absorption in this age group of vitamin B12 from foods that come from animals [7].

http://www.webmd.com/drugs/drug-60350-Aca+B-12+Inj.aspx?drugid=60350&drugname=Aca+B-12+Inj&pagenumber=6:

Aca B-12 Inj
Back to Drug Overview
Does this medication have side effects?
The following side effects are associated with Aca B-12 Inj:
Infrequent side effects:
Itching Less Severe
Diarrhea Less Severe
Rare side effects:
Life Threatening Allergic Reaction Severe


http://www.drugs.com/mtm/b-12-resin.html

What happens if I overdose?
Seek emergency medical attention if you think you have used too much of this medicine. An overdose of cyanocobalamin is not likely to cause life-threatening symptoms.
[...]
B-12 Resin (cyanocobalamin) side effects
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Stop using cyanocobalamin and call your doctor at once if you have any of these serious side effects:
chest pain or difficulty breathing; or
unusual warmth, redness, or pain in an arm or leg.
Less serious side effects may include:
headache or dizziness;
upset stomach or diarrhea;
numbness or tingling;
fever;
joint pain;
stuffy or runny nose, sore throat, nasal pain;
swelling; or
itching or rash.
This list is not complete and other side effects may occur. Tell your doctor about any unusual or bothersome side effect.


http://vitamins-nutrition.org/vitamins-guide/vitamin-b-12-cyanocobalamin.html

Overdose:
Signs of Overdose:
When taken in conjunction with large doses of vitamin C, nosebleeds, ear bleeding, or dry mouth may occur.
Side Effects:
Reaction or effect : What to do
Diarrhea : Stop use and call doctor.
Skin itching : Obtain emergency treatment immediately


http://www.vitamindeals.info/articles/vitamin-b12.html

What Happens If You Get Too Much Vitamin B12?
Symptoms of a B12 overdose are unknown. There is no sufficient, reliable information about the safety of very large amounts.

...and finally, for pure entertainment purposes, from syl.com, a dating service site: :)
http://www.syl.com/hb/toomuchofagoodthinganoverdoseofvitaminb12.html

During World War II, vitamin B12 was given to soldiers before a battle. It was noticed that workers, who were given the vitamin B12, looked calmer. By 1937 manufacturers enriched flour with the vitamin B12. The Medical Institute says that the overdose of vitamin B12 with food doesn't influence the human body in a bad way. The vitamin B12 side effects are very seldom. But they appear when a person suffers from any chronicle disease.
World War 2 ended in 1945. B12 was discovered in 1948.

[Korn]

From http://www.cqs.com/amalgam.htm


15. Methyl mercury is more toxic to some body processes than inorganic mercury. Mercury from amalgam is methylated by bacteria and candida albicans in the mouth and intestines(51,81,98,182,225). Oral bacteria streptococommus mitior,S.mutans, and S.sanguis were all found to methylate mercury(81). High levels of Vit B12 in the system also have been found to result in increased methyl mercury concentrations in the liver and brain(51). Methyl mercury is 10 times more potent in causing genetic damage than any other known chemical (Ramel, in(35)), and also crosses the blood-brain barrier readily. Once mercury vapor or methyl mercury are converted to inorganic mercury in cells or the brain, the mercury does not readily cross cell membranes or the blood-brain barrier. Thus mercury has a very long half life in the brain. N-acetylcysteine(NAC) has been found to be effective at increasing glutathione levels and chelating methyl mercury(54,126).

[Korn]

B12 has several functions, some of them related to cell division and cell growth. Cancer is caused by abnormal and uncontrolled cell division.

Now, findings about what may be beneficial for cancer patients may not at all be valid for others, but here's (http://findarticles.com/p/articles/mi_m0EIN/is_1995_Feb_15/ai_16515543) a study confirming the effect B12 has on cancer cells:


We have demonstrated for the first time that the simple depletion of vitamin B12 - an essential enzyme co-factor for cell proliferation, can trigger programmed cell death in cancer cells without exposure to toxic chemotherapeutic drugs or radiation," said Dr. A. Charles Morgan, Jr., Ph.D., president and chief technical officer of Receptagen.

Receptagen's therapeutic approach involves growth blocker drugs designed to selectively deplete cancer cells of vitamin B12, an essential nutrient for cell growth and division. Vitamin B12 depletion is a treatment approach that has been used to successfully treat patients with acute leukemia. But until now, drugs capable of B12 depletion have not been in existence.

So - B12 doesn't only stimulate normal growth in children, it's essential for cancer cell survival as well.

Again - this isn't an argument for a B12 depleted 'lifestyle', but since cancer is presently responsible for about 25% of all deaths in US and other so called 'developed' countries, maybe it's worth thinking of the possible side effect too high B12 levels can have - not only for people with a cancer diagnosis, but for the millions of people who will develop cancer in the future but don't know it yet.

Some people claim that one cannot take too much B12, but IMO we should look at all the possible effects of too much B12, not only intoxication as a result of overdosing B12, but also possible side effects and on health issues associated with high B12 levels. If you google 'vegan' and 'cancer', you'll find a lot of info confirming that vegans are less likely will develop certain types of cancer than 'normal' people, and as we know, vegans normally have lower levels of B12 than non-vegans (often too low, which of course isn't good either).

[Michael Benis]

It's essential for lots of groth and maintenance process and a deificinecy can slow these. Sure. So?

Anyonetaking in more B12 than they need within levles not induced by massive oversupplmewntation will simply store the excess. It will not alter tissue levels of B12.

[Korn]

It will not alter tissue levels of B12.B12 mainly is stores in muscles and liver, and since 'tissue' is often used about muscle/liver ('muscle tissue', 'liver tissue'), I don't think I understand what you mean....? Here's one article discussing B12 levels in liver tissue: The Vitamin B12 Content of Human Liver Tissue and Its Nutritional Significance (http://bloodjournal.hematologylibrary.org/cgi/content/abstract/12/1/24) The fact that so many people carry around so high B12 amounts in their liver that it could be used as a B12 reserve for years to come somewhat suggests that they consume way too much B12. This, combined with the fact that so many people (meat eaters) who live on a diet that as such isn't B12 deficient also are very low in B12 suggests the amount of B12 humans consume only represent one (possibly overrated) factor in terms of what actually matters when it comes to maintaining a healthy level of B12.


Anyway, here's some more info about B12 allergy (which is rare):
Allergy to hydroxycobalamin, with tolerance of cyanocobalamin (http://www.mja.com.au/public/issues/177_03_050802/h-smith_050802.html)