Anyone who has been vegan for any substantial length of time has been asked about a variety of mythological deficiencies in the vegan diet. Historically, the vegan diet has been characterized as being dangerously deficient in protein, iron, calcium and other essential nutrients. (1) Vegans and vegetarians were constantly warned of the need to supplement their diets with pills, and urged to abandon the extreme, unhealthy diet of fruits and vegetables.
Science ultimately proved all these deficiency myths untrue. Within the pages of this magazine is ample proof that a vegan diet provides more than sufficient protein, even for those pursuing demanding athletic pursuits or wanting to build muscle. And time has shown that a vegan diet can provide more than sufficient calcium and iron for our needs. (2,3) One alleged deficiency in the vegan diet persists however. The “last stand” argument is that a vegan diet is woefully deficient in vitamin B12, and that without substantial and constant supplementation, vegans run the risk of dying of heart disease, or of suffering from dementia, neurological disorders, anemia and other maladies associated with or at - tributed to vitamin B12 deficiency.
If these concerns were true, one would expect vegans to be dropping like fall leaves from heart attacks, or wandering the streets by the thousands demented and anemic on numb or tingling feet. In fact, vegans suffer far less often than their meateating counterparts from these maladies. (4,5,6) Still anyone who has heard the arguments about deficiency would likely have serious questions about B12. What is vitamin B12? How much do we need? Are there vegan sources of B12? Should we be supplementing? Let’s explore the latest science on our quest for answers.
What is Vitamin B12?
Vitamin B12, also known as cobalamin, is a substance that is only produced (as far as science knows at this time) by certain types of bacteria. These bacteria are present in the human mouth and digestive tract, as well as the mouth and digestive tract all other animals. B12 is used by the body to make red blood cells, produce myelin (the fatty substance that forms a protective barrier around nerves), produce acetylcholine (a neurotransmitter that helps with memory and learning), and help produce DNA and RNA. B12 also plays an important role in metabolizing proteins like methionine. Until very recently, the conventional wisdom was that an - imal products were the sole sources of vitamin B12. In fact, many studies of B12 in vegan diets started with the premise that the vegan diet contains no sources of B12. That presumption was always curious, given the fact that it has been known for quite some time that all of the B12 found in animal sources is produced by bacteria which are relatively common in the environment. Nonetheless, the science regarding how much B12 is actually provided by various dietary sources has substantially evolved, and we now know that B12 can be obtained from a number of plant-based sources.
Why is B12 Important?
Vitamin B12 plays a role in a number of vital biological processes, including the production of blood cells, the maintenance of a healthy nervous system, and the metabolism of certain proteins and other compounds. Without B12, the body cannot make functional blood cells, leading to a life threatening form of anemia. B12 is also vital to the maintenance and creation of nerve tissue, so a B12 deficiency can potentially cause numbness or tingling in the extremities (peripheral neuropathy). B12 deficiency has also been associated with various cognitive and neuropsychiatric defects in the elderly. As a general rule, raising low blood levels of B12 provides an effective treatment for all of these maladies, with the exception of neuropathy that has been left untreated for a substantial period of time. (23, 24)
How much B12 do I need?
The body uses only a miniscule amount of Vitamin B12, approximately one millionth of a gram per day, and can store 2-3 mg of B12 in the liver and other body tissues, enough to last 5-6 years. (7) The RDA for B12 for an adult is only slightly more than 2 millionths of a gram per day, and that level assumes that slightly less than half of the amount ingested will actually be absorbed. Given that we need so little B12, and can store so much of it, one would think that B12 deficiency would be extraordinarily rare and relatively easy to remedy.
While it is likely true that genuine cases of B12 deficiency are rare, a substantial amount of controversy has arisen over the amount of B12 people should be consuming due to confusion regarding the best means of testing people for B12 deficiency. This confusion arose due to the role B12 plays in metabolizing two compounds in the body: homocysteine and methylmalonic acid.
Homocysteine, methylmalonic acid, and B12 deficiency testing
One of the roles vitamin B12 plays in the body is in the “methionine cycle,” where the amino acid methionine, which is commonly found in large quantities in meat, is converted to homocysteine, and the homocysteine is then either turned back into methionine, or turned into cysteine. This process, as we understand it, is very complicated, and requires a number of steps and various cofactors to complete. One of these cofactors is vitamin B12. But folate is also an essential part of this process, so is betaine, and so are numerous other enzymes. (9)
It is thought that when the “methionine cycle” becomes unbalanced, homocysteine that is created during the process is not converted back to methionine or cysteine, resulting in an elevated level of homocysteine in the blood. Elevated blood homocysteine levels are commonly found in people suffering from heart disease, Alzheimer’s, and a number of nervous system disorders. (8) Experiments have shown that elevated homocysteine levels can be reduced by adding B12 or folate supplements to a person’s diet.
Because of this, it was suggested that anyone with an elevated homocysteine level, regardless of whether their blood serum level for B12 appeared normal, must be suffering from a B12 deficiency, because homocysteine levels would go down if the body had access to enough B12. The problem with this assumption of course is that the process is complex, and we simply don’t know if a high homocysteine level really means that a person does not have adequate B12 in their system, or if it means that some other element of the equation is out of balance, perhaps from getting too little folate, too much methionine, etc. Accordingly, this test has been criticized for leading to false diagnoses of B12 deficiency. (9)
Another role played by vitamin B12 is in the regulation of methylmalonic acid (MMA) in the body. MMA is produced from the metabolism of branched chain amino acids like valine and leucine. As with homocysteine, B12 plays a role in converting MMA to other substances, so it was assumed that an elevated level of MMA must indicate a shortage of B12. Over the course of the last 10-20 years, MMA tests became the “gold standard” for determining B12 deficiency. Up until about then, it was assumed that a blood test for B12 showing at least 170 pg/mL was a normal B12 level. However, given the large number of people who tested normal for B12, but high for MMA or homocysteine, many health practitioners started urging that a “normal” B12 level should be double, triple, or even more than that amount in order to make sure that MMA or homocysteine levels stayed low. (9)
However, the use of MMA tests, just like homocysteine tests, has been criticized for the fact that reliance on those tests assumes a lot about how MMA is metabolized by the body that isn’t really supported by the science. First, reliance on those tests assumes that under normal conditions the body will utilize all available B12 to reduce levels of MMA. However it is also possible that the body will process a certain amount of MMA in a given time period under normal conditions, allowing MMA levels to remain high for a period of time. It is also difficult to say with any certainty what a “normal” level of MMA is under a variety of circumstances given how little we know about the process. There are also a number of other factors besides levels of circulating B12 that can lead to high MMA levels. Further, as with homocysteine tests, MMA tests can show high levels of MMA even under circumstances where B12 levels are so high that a deficiency clearly does not exist, and so the test is just as capable of leading to false positive results. For that reason it has been criticized as potentially leading to over-diagnosis of B12 deficiency.(9)
Given these valid criticisms, consuming massive quantities of B12 just to drive down levels of homocysteine or MMA levels without any other indication that a B12 deficiency may exist is simply treating test results rather than an actual malady. The truth of the matter is that as yet we do not have one agreed upon test for determining B12 sufficiency. The best method recognizes that nutrition is a complex science, and takes into account a person’s lifestyle, diet choices in evaluating bloodwork, and not just relying blindly on one test.
With that in mind, there are some important dietary, health and lifestyle factors that can affect how much B12 from the diet is actually absorbed. In fact, it is relatively widely accepted that most cases of B12 deficiency are not due to inadequate intake of B12, but rather to problems associated with its absorption by the body.
Factors affecting the absorbability of B12 Alcohol, smoking, and drugs The consumption of alcohol, smoking, and a number of prescription drugs, including some cholesterol medications, have all been shown to decrease absorption of B12. (10,11,12) Vitamin C and potassium can also damage the structure of Vitamin B12, so taking large doses of Vitamin C along with a source of B12 can conceivably prevent its absorption (which is what is frequently done when a multi-vitamin is utilized). (6) Also, over-the-counter antacids such as Prilosec, Zantac, Tagamet and other such medications can decrease the production of acid and the so-called “intrinsic factor” by the stomach lining. (13) These two substances are vital to the absorption of B12 from food, so the chronic use of antacids can potentially hamper the digestion of B12. As with all such medications, the best approach is to find the cause of the digestive discomfort and treat that directly, rather than just treating the symptoms of the underlying problem with medication.
In the stomach, B12 is separated from food by “intrinsic factor,” a compound secreted by cells in the stomach lining that bind to B12 and transport it to the ilium where it is absorbed by the body. Intrinsic factor is vital to this process, without it the body cannot absorb B12 from food. When the stomach does not produce intrinsic factor a person will go through their body stores of B12, and then develop a condition known as pernicious anemia. Generally, this condition causes symptoms of extreme gastric discomfort, along with other unique symptoms such as a smooth red tongue, so there is some warning that the digestive system is not operating properly and needs tending to. (25) Also, occasionally the digestive system can become overpopulated with bacteria that actually consume B12, which essentially steal B12 before it can be absorbed by the body.
That condition is known as Small Intestinal Bacterial Overgrowth. The symptoms of the disease include chronic digestive discomfort and weight loss. When a person suffers from this disease, the body is absorb - ing less B12, so it starts to use up stored B12, and if the problem persists for several years those stores can be depleted, leading to symptoms of B12 deficiency. Again, maintaining a healthy diet and lifestyle will help maintain a healthy balance of bacterial flora in the digestive system, and is probably the best protection against this disease. (26)
Can I get B12 in a vegan diet?
The short answer to this question is yes, it is highly unlikely that you wouldn’t be able to find sufficient sources of B12 in a vegan diet. The amounts in vegan foods may be small, but remember, the body only needs a very small amount and is quite good at stor - ing it for many years.
For starters, many vegan foods, including various non - dairy milks, cereals, breads, tofu and a myriad of other vegan products are routinely fortified with B12. So a few servings a day of these items easily provide you with more than 100% of the RDA for B12. But there are plenty of whole food sources of B12 as well.
It once was thought, incorrectly, that only animal foods contain B12. In fact, you will still find that claim repeated on many health-advice internet sites. But that is simply not the case. B12 is produced by bac - teria, not animals, and those bacteria can be found in many fermented foods, such as tempeh, kombucha, and some types of kimchi and sauerkraut, and can also be found in a number of other plant sources such as some types of seaweed and even some fermented teas. (14,15,17,18,19,20,27). Also, it has been shown that plants such as spinach, barley and certain types of radish can absorb B12 from the soil in which they are grown. (14) B12 is thought to be easier to absorb from whole foods than it is from pills or powders, so it is probably best to get B12 from whole foods whenever possible (it is assumed that about 50% of the B12 in food is absorbed by the body, whereas it has been shown that only about 1% of the B12 in high-dose supplement form is absorbed). (7) Included at the end of this article is a list of vegan foods that have been found to contain B12.
So do I need to supplement with B12?
As with anything, it pays to do your own research and come to your own conclusions. However, the latest science does show that it is possible to obtain sufficient B12 from a vegan diet. As long as you avoid be - haviors that can decrease your B12 absorption such as chronic smoking or drinking, and maintain a healthy digestive system, you should be able to absorb more than enough B12 from a vegan diet.
Is there a downside to supplementing?
The general consensus is that it is not possible to overdose on B12 supplements, particularly since only about 1% of the B12 that is ingested in pill form is actually absorbed by the body. This belief is one of the reasons that some health practitioners routinely advise vegans to take B12 supplements that contain a hundred or more times the RDA of B12. After all, if there is really no downside to taking a supplement, isn’t it better to be safe than sorry.
However, just because there is no evidence at this time that taking a B12 supplement itself causes harm does not mean that regular B12 supplementation can’t have negative consequences. One potential adverse consequence has to do with the fact that B12 supplementation can mask the symptoms of serious underlying diseases. For example, if you have pernicious anemia – which generally results from damage to the cells in the stomach lining that secrete the “intrinsic factor” necessary for the absorption of B12 from food – regular B12 supplementation will mask some of the symptoms of the disease, potentially allowing it to progress to the point where treating or reversing the underlying condition may become more difficult. Or worse, it may progress to the point where B12 is no longer absorbed from food, leaving the person with an undiagnosed and dangerous condition where suddenly stopping B12 supplementation could cause a life threatening anemia. Also, in cases of Small Intestinal Bacterial Overgrowth, where overgrowth in the small intestine of anaerobic bacteria that consume B12 before it can get absorbed by the body, regular supplementation with large doses of B12 could conceivably foster the growth of such bacteria, worsening or prolonging the absorption problem, and the gastric discomfort that would go with it.
Additionally, an imbalance in the metabolism of MMA or homocysteine can be due to a number of nutritional deficiencies or diseases. Regular supplementation with B12 can mask those problems by making it appear that the metabolic cycle is in balance when it is not, allowing potential deficiencies in folate, B6 or other nutrients to go undetected, or worse, mask some of the symptoms of serious kidney or other diseases that can also increase levels of MMA or homocysteine. (9)
Finally, it is not necessarily certain that consuming frequent massive doses of artificially prepared vitamin B12 will not have long term negative health consequences that we have not discovered yet. There can be little argument that the intake of such high levels of B12 does not occur naturally, and it may well be that maintaining an unnatural state of chronic, extremely high B12 intake could lead to as yet undiscovered consequences. That certainly has been the case with other isolated vitamin supplements that we once thought were beneficial, such as beta carotene and vitamin E, which we discovered actually increased the risk and progression of certain cancers. (21)
Food for thought: Is B12 really a “vegan” issue at all?
The claim that a vegan diet is devoid of vitamin B12 is one of the last great “deficiency myths” about veganism. If there were really much truth to it, most vegans would, within 5-10 years of going vegan develop anemia, neurological defects, and other symptoms of the disease. But the simple fact is that not a single large scale study of long term vegan health issues has ever found that to be the case, despite rather extensive findings that vegans do not consume the amounts of B12 that many practitioners believe is necessary to ward off a B12 deficiency.
Further, recent studies show that B12 “deficiency” is as much of a problem for meat and dairy eaters as it supposedly is for vegans. In a large scale study of the residents of Framingham Massachusetts, it was discovered that meat and dairy eaters who did not take B12 supplements had below normal B12 blood serum levels. (16) It is curious, given these findings, that any medical professional would characterize B12 deficiency as a problem primarily suffered by vegans, since the evidence shows that it appears to be just as much of a problem for meat eaters. Further, the fact that only people taking supplements in this study appeared to have “normal” blood levels of B12 suggests that our idea of a “normal” B12 level may be too high, particularly since there does not seem to be any indication that the residents of Framingham are disproportionately suffering numbness of the extremities, anemia, or any of the other symptoms of B12 deficiency despite the high numbers of supposedly “deficient” residents.
In any event, given this data, it is simply not accurate to describe B12 deficiency as a problem suffered mostly or even disproportionately by vegans. Doing do only perpetuates the myth that a plant-based diet is somehow inferior to or deficient in nutrients found in an animal based diet. This unnecessarily frightens many people away from a diet that has been shown to increase longevity and vitality and decrease the risk of death from cardiovascular disease, cancer, and a host of other diseases. (22)
Nutrition science is a relatively young field, and is constantly evolving. With respect to vitamin B12, what we can at this point say for certain is that a healthy, varied vegan diet that includes a lot of different sources of nutrients can provide sufficient vitamin B12. If you choose to supplement your diet with B12 in pill or powder form, just be aware that the body absorbs much less B12 from artificial high-dose sources, about 1% (which means you are literally flushing 99% of the pill down the toilet). Nonetheless, you should try to tailor your supplementation so that you are not vastly exceeding the RDA.
What plant-based foods have been found to contain B12?
In addition to the myriad of fortified foods in the marketplace, the following foods have naturally occurring B12:
A survey of various plant-based foods for B12 content found that tempeh can contain fairly large amounts of vitamin B12 (0.7 to 8 μg/100 g).(14) That amount is as much or greater than the amount of B12 contained in a serving of meat, eggs, or milk. This finding should not be that surprising, given that the fermentation process relies heavily on bacteria, and a number of studies have found that the bacteria used to make tempeh can include strains that produce B12. (14, 18, 19)
The same study noted above found that “nori” (seaweed) can contain large amounts of B12 (32 to 78 μg/100 g dry weight). This amount equals or exceeds even the highest amounts provided by some animal sources of B12. The study showed that vegans who consumed nori had serum vitamin B12 concentrations twice as high as those not consuming nori. Further research with Nori has confirmed that the B12 present is in fact a biologically active form of B12 . (14,17, 20)
Perhaps one of the most surprising of sources of B12 is fermented tea leaves. A study found that considerable amounts of vitamin B12 are found in various types of tea leaves: green (0.1–0.5 μg vitamin B12 per 100 g dry weight), blue (about 0.5 μg), red (about 0.7 μg), and black (0.3–1.2 μg) tea leaves. (14)
Kombucha has also been found to contain substantial amounts of B-12, up to 840 mg/L. (15) In fact many (though not all) brands of kombucha now list the B12 content right on the label.
SAUERKRAUT AND KIMCHI
Kimchi and sauerkraut made with strains of propionibacteria are fermented foods that have also been found to contain substantial amounts of B12, up to 7.5 μg/100g. (27)
Some nutritional yeasts are either fortified with B12, or use a fermentation process that produces B12. For the nutritional yeasts that do contain B12, one tablespoon will generally provide half or more of the daily B12 RDA. The label will tell you if it contains B12, and how much (29)
Several types of mushrooms have been found to contain substantial amounts of B12. Golden chanterelleand black trumpet mushrooms were found to contain between 1.09-2.65 ug/100 g of B12 (30), dried shitake mushrooms were found to contain 5.62 ug/100g (14), and white button mushrooms were found to contain B12 as well (.26 ug/100g). (31)
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