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How to Handle Vitamin B12 Deficiency on a Vegetarian Diet

Vegetarians and B12

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Over the last year, I have been eating more vegetarian meals. Part of this has been motivated by the reality that almost all meat served at restaurants is factory raised.

I even went Vegan for a week as an experiment. I still eat meat and fish on average about once or twice a week, but I have cut back on my intake of animal protein. In addition to environmental concerns, I went cut back on meat because it works to keep my lipid numbers in a range I am comfortable with, and I have a few genetic indicators that point to success on a plant based diet, among them some of my protein metabolism genes, and my blood type is A+, which is associated with lower levels of hydrochloric acid in the stomach (the less hydrochloric acid, the lower the ability to digest large amounts of animal flesh).

Vegetarians are Prone to B12 Deficiency

But here’s the issue: vegetarians, and especially vegans, have a tough time getting enough Vitamin B12, an essential nutrient that pretty much only comes from animal sources, such as eggs, chicken, beef, and dairy products. Even Vegan advocates in documentaries like The Game Changers concede that Vegans will do best if they take supplemental B12.

As an aside, if you’re planning on getting your B12 from eggs, think again, the bioavailability of the B12 in eggs is low, and it’s especially low if you eat your eggs scrambled as I do. 1

If you’re not getting enough B12, you likely won’t feel your best. B12 deficiency can trigger symptoms such as anxiety, problems with sleep, low energy and even memory loss. However, a true B12 deficiency is tough to identify and can take years to develop.

In my case, I was somewhat low on B12 before I went on a vegetarian diet. When I had my B12 levels tested, the results at 400 pg/ml, were in range, but on the low side. Quest Diagnostics lists 200-1,100 pg/ml as the “normal range” for vitamin B12 levels. Here is probably a good place to mention that some clinicians don’t love serum nutrient tests as they tend to measure the amount of that nutrient in the blood, rather than the amount of the nutrient that has entered the cell.

Since I transitioned to a more plant based diet, I have noticed an extra “boost” from B12 supplementation, both from shots and capsules. My suspicion was that removing some of the meat from my diet put my B vitamin levels on the low side, and this was confirmed with a recent SpectraCell test. According to SpectraCell, which measure for nutrient absorption at the cellular level, I was deficient in zinc, oleic acid and omega 3 fatty acids, and borderline deficient in many B vitamins, including B12.

Vitamin B12 and Genetics – MTRR

I also have a homozygous mutation in an MTRR SNP, which is a gene associated with B12 metabolism, so genetics could play a role in my ability to maintain optimal levels of B12. Aaron had this to say about how MTRR and B12 work in tandem:

B12 is the major cofactor for methionine synthase (MS), when bound MS can process homocysteine into methionine. However, over time this vitamin B12 molecule loses its effectiveness and must be removed from MS. Enter MTRR; which removes the old B12 molecule allowing a new functional one to bind. So B12 deficiency doesn’t tie in directly with MTRR, but a lack of MTRR activity can appear very similar symptomatically.

B12 Deficiency and Gut Health

Another factor to consider is gut health. If your microbiome is out of balance, it will be that much more difficult to absorb nutrients from food. 2 For example, the holistic blogosphere is full of articles linking small intestine bacterial overgrowth (SIBO) to B12 deficiency. In my case, I had a bout of histamine intolerance after moving to Austin. Histamine intolerance is a problem that essentially begins and ends in the gut.

For further research, Leigh also wrote an excellent blog post recently about the genetics of nutrient absorption which is worth a read.

When you add MTRR genes to a vegetarian diet that is high in the anti-nutrient phytic acid (which further prevents nutrient absorption) you have the perfect storm for B12 deficiency.

B12 supplements might not be enough

But here’s the thing: it’s not as simple as just going out and supplementing with B12, or any other B vitamin. If you’re committed to a vegetarian lifestyle, you need a strategy to get as much B12 as possible from plant sources and caution should be exercised with dosing if a supplement is needed.

As we discuss in our recent blog on the link between B vitamin supplements and cancer, mega doses of folic acid, B6 and B12 are generally to be avoided, especially over the long term.

For long term B12 supplementation, data suggests that it is a good idea to stay well beneath a daily dose 0.4 mg, or 400 mcg. Higher doses may increase cancer risk. Our research shows that cancer risk was not increased for those who took B vitamins as part of a multivitamin, with Aaron theorizing that the B2 played a protective role.

Putting all of that information together, the play, if B12 supplements are being considered at all, is to go with conservative dosing, which is very tricky to find in standalone B12 supplements, and to combine your B12 with a B complex supplement that contains B2, or in a multivitamin with a cocktail of other nutrients. Most manufacturers that isolate B12 into a single product feel like they need to give consumers “their money’s worth,” and so they pack in either 1,000 or 5,000 mcg doses.

Avoid these supplements.

To borrow from the B vitamin and cancer risk post I cited to above, we found that B complex formulas by both Thorne and Pure Encapsulations offered nice conservative B12 doses that were well below the 0.4 mg threshold we want to stay under.

Vegetarian B12 supplements

B-Complex100 mcgLower dose B12 considered safer by some studies. Thorne B6 dose on high side.
Dried green laver (Nori)63.6 mcg63.6 mcg/100 g per dry weight. Enteromorpha sp species.
Purple laver (Nori)32.3 mcg32.3 mcg/100 g dry weight. Porphyra sp species.
Lion's mane1.09–2.65 mcgHericium erinaceus. Approximate 1.09–2.65 μg/100 g dry weight.
Chlorella tablets100 mcgEukaryotic microalgae Chlorella sp. Dose varies considerably by product, check labels. Based on 100g of dried weight.

What about B12 shots?

Amber wrote about her experience with B12 shots recently, which is worth a read. When I am deficient, I will take a B vitamin shot for a few weeks in a row with doses of B12 around 1,000 mcg as a catch up. When I do opt for shots, I make sure that the shot contains B2 as part of the formula and I am careful to cycle on and off these doses as I feel I need them. As a general rule, I will never take more than 3-4 B vitamin shots a year.

Getting Vitamin B12 from plants

In an ideal world, every vegetarian would have access to a quarterly SpectraCell test that would keep an eye on vitamin B levels and provide a useful gauge on the necessity of supplements. However, even if you’re “flying blind” and creating a supplement stack without the aid of data, it is wise to try to get as much of your B vitamin intake as possible from plant sources. This is especially true in light of the studies that link B vitamin supplements to increased risk of cancer.

So, what are the best plant sources of B12 and how bioavailable are they?

A note on B12 Analogs and “fake” B12

Many of the reputed natural, plant based sources of B12 are actually paper tigers in that they appear to offer B12, but the form of B12 they contain isn’t usable, or “bioavailable” for humans. For example, using chromatography testing, researchers have isolated plant compounds in algae and mushrooms that are known as “corrinoid compounds,” which mimic B12, but which are inactive in humans.

Spirulina is a good example. Although the marketing machines behind these products claim Spirulina has ample B12, these plants actually contain fake B12, which can test as B12 in some labs, but additional research has shown these are false positives, and the actual B12 count is very low. 3

The plant sources of B12 recommended below have been confirmed through laboratory testing to contain usable forms of B12.

What are The Best Plant Sources of Bioavailable B12?


Popular in Japan, and also called laver, Nori is a sea vegetable that has high amounts of bioavailable B12, as well as iron. 4 Nori provides one of the best, if not the best, plant based option for vegetarians looking for more B12 in the diet. Nori is widely available online and comes in dried flakes that can be sprinkled on salads, in smoothies, or even added to most dinner entrees. I have seen a few of the Vegan families at Casa de Luz in Austin sprinkling Nori flakes on their kid’s food.

Note: only two species of Nori contain bioavailable B12: dried green laver (Enteromorphasp.) and purple laver (Porphyra sp.)

To quote this article on vegetarian nutrition that appeared in the Journal Nutrients, most other forms of algae have only trace amounts, if any, B12:

Dried green laver (Enteromorphasp.) and purple laver (Porphyra sp.) are the most widely consumed edible algae, and they contain substantial amounts of Vitamin B12 (approximately 63.6 μg/100 g dry weight and 32.3 μg/100 g dry weight, respectively). However, excluding these two genera, other edible algae contain zero or only traces of Vitamin B12. 


Although none of these mushroom species by themselves will give you anywhere close to your daily recommended amounts of B12 (you’d have to eat 50g a day of dried shiitake to meet your daily B12 requirements), they are useful to keep on the radar to add to the B12 bucket.

Remember, the strategy here is to be able to take a low dose B12 supplement and get the rets of what you need from food.

Shiitake, black trumpet, golden chanterelle and Lion’s mane all contain some bioavailable B12 to give an “assist” on the vegetarian diet. 5 6 7

Chlorella tablets

Chlorella tablets, which are a species of micro algae, have also been determined to be good sources of supplemental B12. 8

Closing thoughts

If you’re on a vegetarian diet, there are health advantages, but it’s also clear that you risk B12 deficiency.

Because high dose B12 over extended periods of time has been linked to an increased risk of cancer, finding plant foods that can “top off” your B12 levels will be key. In addition, maintaining or restoring gut health is a top priority as the state of your microbiome will affect absorption.

Shiitake, black trumpet, golden chanterelle and Lion’s mane mushrooms are a good bet, as are very specific species of Nori, which can be sprinkled on food or blended in a smoothie.

John O'Connor

John O'Connor is the founder of Gene Food, host of the Gene Food Podcast and a health coach trained at Duke's Integrative Medicine Program. Read his full bio here.

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