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Home Blog VITAMIN B12


03.11.2018 / By Sonia Raga / Published in NUTRITION


What is B12?

Vitamin B12, also known as cobalamin, is a water soluble vitamin that plays an important role in the body. It is involved in the synthesis of DNA, the correct functioning of the nervous system and in the metabolism of every cell in the human body.


Many people think that animals are the primary source of vitamin B12, which is not the case. Plants nor animals can synthesis vitamin B12. Only anaerobic bacteria living in the soil and water can do so (these microorganisms synthesize vitamin B12 from the mineral cobalt).


When ruminants (for exemple cattle) eat grass, they ingest B12-producing bacteria which is then “stored” in their rumen. The rumen (the first stomach of ruminants) is the perfect environment for this anaerobic bacterias. That’s why ruminants do not need a direct source of B12, since they are actually ingesting the bacteria that synthesizes it and which populates their stomach.



Our human ancestors got their vitamin B12 in a similar way, since they spent most of their time foraging tubers and roots, which they ate unwashed, getting therefore enough vitamin B12 to maintain a proper status. They also ate some bugs, insects and other animals products, which also contributed to their overall B12 intake.


Nowadays, we live in highly sanitized societies where the soils are very poor in microorganisms and minerals due to massive exploitation. Our vegetables are sprayed, scrubbed and washed to the point that they are not a reliable source of vitamin B12 anymore. That’s why people avoiding animals products must rely on a vitamin B12 supplement or consume fortified products to meet their B12 needs.


As explained above, animal foods are not the primary source of vitamin B12. We can get our vitamin B12 from these B12-producing bacteria instead of from animal products. A benefit of doing so is, we avoid at the same time the richest sources of cholesterol and saturated fat, which are the main cause of the number one killer in modern societies: heart disease.



Should all vegans take a B12 supplement?

There are no reliable plant-based sources of B12. Therefore, supplementation or relying on fortified foods is a must.



I read that certain plant foods contain vitamin B12. Is that true?

You might have heard or read that certain plant foods, such as spirulina, contain B12. However, these are NOT reliable sources of B12. Many plants contain inactive analogs that can disrupt B12 metabolism and may give false positive results in B12 check ups. I personally avoid spirulina, also because some studies showed that spirulina intake could affect the nervous system.


You might have also heard that miso and tempeh are reliable sources of B12, but they are NOT.


The seaweed nori has been found to contain substantial amounts of active B12 but there is still some uncertainty to it, so it should not be considered a reliable source of B12 until more research has been done. It is important to understand that even if an active form of B12 is present in a food, it might be useless if there are comparable amounts of analogues as well.


transparent bowl with seaweed salad

Photo by Ana Tavares on Unsplash


B12 deficiency symptoms

The most common symptoms are numbness or tingling in the hands and/or feet as well as tiredness and weakness. Other symptoms are heart palpitations, memory loss and/or vision loss. When the intake of vitamin B12 is insufficient, the red blood cells cannot divide properly, resulting in megaloblastic anemia or also called macrocytic anemia.



Health consequences of B12 deficiency

B12 deficiency should be taken seriously since it can cause a wide variety of serious health problems such as megaloblastic anemia, birth defects (neural tube defects), developmental delays in children, neuropathy and sustained spinal cord degeneration, memory and cognitive impairment as well as a high homocysteine status which is related to adverse pregnancy outcomes such as preeclampsia, placental abruption, preterm delivery, and low birthweight.



Should I get my B12 levels checked?

Absolutely yes. If you decide to go vegan, make sure to check your vitamin B12 levels before doing starting out and every 6 months to a year since then (follow your physician’s recommendations).


Obviously, start taking a B12 supplement not later than 2-3 months after going vegan. Although the body typically has sufficient vitamin B12 stores to last for a few years, the speed at which vitamin B12 deposits get depleted varies greatly among different people. Therefore, it is not worth taking any risk. So, if you decide to go vegan, start taking a B12 supplement as soon as possible.



Is it dangerous to take too much vitamin B12?

Since vitamin B12 is a water soluble vitamin, any excess will be excreted with the urine, so you don’t really need to worry about overdosing. However, make sure to follow the directions of a physician and don’t take more than strictly necessary. High doses of B12 have been related to acne in sensitive people. If you are an acne-prone person, make sure you are not taking more than you really need.



B12 status: serum B12 levels, homocysteine and methylmalonic acid.

Serum/plasma concentrations is an accurate, practical and inexpensive way to measure B12 status.


Homocysteine and Methylmalonic acid levels are good markers of B12 status since inadequate intake of vitamin B12 leads to elevated plasma homocysteine as well as elevated serum or urinary methylmalonic acid (MMA).


Often, homocysteine and MMA tests are used to diagnose early B12 deficiency. However, these assays are certainly more expensive and the results might be affected by several other factors, such as poor renal function. Homocysteine levels can also be affected by metabolic problems as well as folate, vitamin B2 and vitamin B6 status (a deficiency in this last two can increase homocysteine levels). Homocysteine can damage the artery walls and high levels of it have been associated with an increased risk of the most common Western diseases, such as heart attacks. People that consume large amounts of animal products also present high levels of homocysteine.



What else can cause a B12 deficiency besides an insufficient intake?

Some people might experience a deficiency in vitamin B12 in spite of a proper intake, which is due to malabsorption of vitamin B12.The most common condition of vitamin B12 malabsorption is pernicious anaemia (PA). To understand it, we need to know what the intrinsic factor is:


The intrinsic factor is a glycoprotein secreted by the stomach’s parietal cells. It plays a key role since it binds vitamin B12 and enables its active absorption. Pernicious anemia is an autoimmune disease where the body produces antibodies that attack the parietal cells which consequently lose their ability to produce intrinsic factor.


In other cases, antibodies are produced directly against the intrinsic factor itself, attaching to it and preventing it from binding vitamin B12. If you suffer from pernicious anemia, you will probably need either higher doses of vitamin B12 of injections. Your doctor should decide the right medical treatment for you.


(Just for clarification purposes, pernicious anemia has nothing to do with veganism. It is an autoimmune disease and it could affect anyone).



Who else should take a B12 supplement besides those following a vegan diet?

According to the Food and Nutrition Board, all people (and not just vegans) older than 50 years old should “meet their RDA mainly by consuming foods fortified with B12 or a B12-containing supplement.” The reason for this statement is that 10 to 30 percent of older people have problems absorbing vitamin B12 due to atrophic gastritis.


Also, “individuals with vitamin B12 deficiency caused by a lack of intrinsic factor require medical treatment.”



How much, how often and what type of B12 should I take?

The RDA for adults is 2.4 µg/day but the amount of vitamin B12 that you need to take as a supplement depends on how often you are going to take it since absorption rates vary significantly. Low doses are much better absorbed which means that if you take your supplement more often, you need lower doses and if you take it more sparingly, you need much higher doses. Whether you do one or another is up to you. Some people find it easier to get used to take a daily supplement while others prefer to take it only once/twice a week.

Whether to rely on supplements or fortified foods is also up to you. I personally prefer to take a supplement so I don’t have to make sure that I’m eating fortified foods every single day.


Types of vitamin B12

Concerning the types of B12, there are 4 forms:

  • Adenosylcobalamin (AdoCbl)
  • Methylcobalamin (MeCbl)
  • Cyanocobalamin (CNCbl)
  • Hydroxocobalamin (HOCbl)


The first two (AdoCbl and MeCbl) are the active forms of vitamin B12 in human metabolism and the body requires both of them.

CNCbl is the form usually present in dietary supplements and fortified foods since it is well studied, the least expensive and the most stable. However, the body must convert CNCbl to the active forms AdoCbl and MeCbl.

HOCbl is the form usually administered parenterally as a prescription medication (intramuscular injection).


cup of tea

Photo by Carolyn V on Unsplash


Existing evidence does not suggest any differences among forms with respect to absorption or bioavailability. However, some researchers suggest that at higher doses, CNCbl is better absorbed. It seems that absorption of MeCbl is more effective by way of intrinsic factor while CNCbl absorption efficiency is better through passive diffusion. According to some researchers, MeCbl and AdoCbl supplements might not be stable in their oral form and thereby much higher doses might be needed. Absorption rates aside, there are several other reasons why some physicians feel more comfortable recommending one or another.


Some physicians do not recommend CNCbl because of the following:

The body must convert CNCbl to the active forms AdoCbl and MeCbl by releasing the molecule cyanide. However, some people can’t make this conversion efficiently, therefore affecting B12 status.


In addition, cyanide molecules accumulate in the body and, in specific amounts, it is known to be highly toxic. On the other hand, cyanide is also present in many fruits and vegetables and some sources consider that the amount of cyanide in CNCbl supplements is physiologically insignificant.


However, it can not be overlooked because certain individuals might need to avoid this form of B12. For example, people at risk for Leber’s optic atrophy, a genetic disorder caused by chronic cyanide intoxication, should definitely avoid CNCbl supplements since cyanocobalamin may increase the risk of irreversible neurological damage. Typical early symptoms of mild cyanide toxicity include dizziness, headache, vomiting, fast heart rate and shortness of breath.


Now let’s focus on the MeCbl form:

Many physicians prefer to recommend MeCbl since it is an active form of B12, meaning it is readily available for cells to use. However, according to some studies the methylated form is unnecessary since the methyl group on MeCbl is removed before the methylcobalamin enters the cell and the cobalamin is later on re-methylated within the cell.


Even if this may be so, many doctors and physicians still prefer the methylated form since according to their experience, it is more effective at reducing homocysteine levels and it has been shown in clinical studies to successfully improve vitamin B12 status of individuals. Many of them also consider that avoiding the possibility of long-term toxicity due to cyanide is an added advantage.



Recommended doses:

As stated above, the RDA for adults is 2.4 µg/day. However, the body’s ability to absorb vitamin B12 from dietary supplements varies significantly depending on the dose.


Common recommend doses are:

  • If relying on CNCbl fortified foods: 2.5- 4 mcg twice daily.
  • Daily supplement: 25-1000 mcg once/day*
  • Weekly supplement: 500-2.500mcg once/twice weekly*

*As you can see, the dose’s range varies significantly. It is difficult to make a particular recommendation since the required intake depends on:

  • The person’s ability to absorb the vitamin.
  • The form of cobalamin taken.
  • Your age and whether you are pregnant or breastfeeding.


The best way to know which is the right dose for you is to test your B12 levels sporadically and make adjustments according to them and in agreement with your physician. In spite of this, the most common recommendation for vegans in general is 1000-2000 mcg once a week.


Many people ask me how much, how often and which type of B12 I personally take: I’ve been taking 1.000mcg of methylcobalamin once a week since 2007 and my B12 status has always been adequate ever since. This is not a recommendation for you. I just share this information for curiosity purposes since I get asked very often.



Maintaining adequate levels of vitamin B12 is highly important to preserve optimal health. If you decide to follow a plant-based diet or a mostly plant-based diet, don’t risk your health and make sure you are either eating B12 fortified foods daily or taking a B12 supplement.


cow and kid

Photo by Jinen Shah on Unsplash


Some people argue that a vegan diet is unnatural because of the need of B12 supplementation. The thing is, we do not leave in natural environments anymore, our food is not what it used to be and our lifestyles are also far from being “natural”. We use cellphones, cars and cleaning products. There are many things our ancestors did that we don’t need (and probably nor want) to replicate. When I analyze our current society, I see three highly alarming facts:


  • Around 70 billion farmed animals are reared annually. Around 6 million animals are killed for food every hour.
  • Coronary heart disease kills around 400.000 people annually. That’s around 8.000 people per week. (For more information, check out Forks over Knives).
  • Animal agriculture is responsible for 18 percent of greenhouse gas emissions, more than the combined exhaust from all transportation. (For more information, check out Cowspiracy)


The good news are, there is one simple thing you can do to stop contributing to all of the above: changing what you put in your mouth every day.


According to the American Dietetics Association, “planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases”. They also confirm that well-planned vegetarian and vegan diets are appropriate for individuals during all stages of the life cycle (including infancy, childhood, adolescence, pregnancy, lactation and for athletes).


In my opinion, taking a B12 supplement is an insignificant compromise compared to all the benefits a plant-based diet has to offer.




Disclaimer: This article is for information purposes only. To decide the type and dose of B12 that you need, consult with your doctor or other qualified healthcare professional.




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