In this article, we will take a closer look at algae as a source of vitamin B12, addressing the following questions:
Plant-Based, Vegan Vitamin B12: It Does Exist
For a long time, official sources stated that vitamin B12 was contained in animal products only and that no plants contained the vitamin. After years of research and multiple mistakes, it is now clear that, on the contrary, plant sources of B12 do exist. Nonetheless, this topic is more complicated than expected. Molecules similar to vitamin B12 – known as vitamin B12 analogues – have often been misinterpreted as the real vitamin; a confusion that has repeatedly led to mistakes and false reports. In the following, we will give an overview of the current research on the topic of plant-based, vegan vitamin B12.
Algae – A Source of Vegan Vitamin B12?
Vitamin B12 is almost exclusively present in animal food sources and is only found in traces in ordinary fruit and vegetables. As a result, vegetarian and vegan diets in particular often contain little to no vitamin B12 sources, which is why there has been intensive research into plant-based B12 for many years.
So far it has only been found underwater: algae have emerged as the sole candidate for a vegan vitamin B12 solution. Even so, the situation is complex and the research positions on this subject have frequently changed over the past decades, leading to many false reports.
In previous tests, almost all algae revealed vitamin B12 analogues instead of the real thing. Analogues are not only ineffective, but also potentially dangerous. Most researchers have consequently dismissed algae as a B12 source and recommend natural B12 supplements as a safe alternative. Despite this, there is one algae called chlorella which could be the building block of a genuine vegan B12 supply.
Vitamin B12 in Algae: Real or Analogue?
In order to properly understand the discussion about the B12 content of algae, it is important to first take a closer look at analogues. Also known as pseudo B12, analogues are molecules which are so chemically similar to real B12 that they bond to the same transport molecule. In contrast, however, they have no vitamin effect on the body whatsoever. This is detrimental to health, as only real B12 that is bound to this specific transport molecule can be used by the body.
When B12 analogues bind to this transport molecule, even when there is a very good dietary supply of the vitamin, B12 deficiency can occur, as the real vitamin simply cannot be transported and utilised.
To read more on this topic, see our article: Vitamin B12 Analogues
Algae and Pseudo Vitamin B12
Vitamin B12 analogues are so similar to the real vitamin that conventional B12 tests cannot differentiate between them; only complex test procedures can make a clear distinction. Over the years, this has led to much confusion regarding plant sources of B12, as analogues have often been falsely identified as vitamin B12.
When assessing a source of B12, it is always important to keep in mind the relationship between vitamin B12 and analogues. In order to ensure a positive health effect, sources should ideally only contain real vitamin B12. At the very least, the content of genuine B12 should be significantly higher than that of analogues.
However, if the content of real B12 is outbalanced by a high content of analogues, B12 deficiency will worsen. This is because the analogues occupy all the transport molecules and thus ensure that the body can no longer utilise the real vitamin.
Vitamin B12 Content of Algae
As we will explore shortly, there are only really two types of algae – chlorella and nori – which can be considered B12 sources. However, both have one significant weakness: their B12 content is not produced by the algae itself, but rather by microorganisms which live on the plant or in the soil.
The B12 content thus depends massively on the growing conditions and presence of these microorganisms; no definitive statement can be made on the exact B12 content of these algae. Even in the same location, levels can rise and fall from one year to the next quite drastically.
At present, the Vegan Society does not consider algae such as these to be an official plant source of B12 and instead advises taking supplements which contain B12 identical to the natural vitamin B12 forms.
Which Algae Contain Vitamin B12?
Before we examine each individual type of alga, here is a brief overview of the candidates currently discussed as potential B12 sources.
Real B12 µg/100g
B12 Analogue µg/100g
Effect on B12 status
Nori (red alga)
Chlorella (naturally produced)
~ 100 µg
< 10 µg
Chlorella (artificially grown, fermented)
When comparing algae in this table, it is worth remembering that the values given here are averages; the actual content can vary significantly from product to product and harvest to harvest.
Spirulina: Not a Vitamin B12 Source
For a long time, spirulina was considered a vitamin B12 source. However, the B12 content in spirulina, which was originally measured by outdated methods, soon turned out to be B12 analogues in various studies (1-3). In fact, the B12 content has been measured to total at just 30%, a very low amount compared to the level of analogues (4, 5).
As expected, taking spirulina significantly worsened the B12 status of a research group in a study, which found that the analogues impaired the absorption rate of the genuine vitamin (6). Vegans, vegetarians and people with B12 absorption disorders should thus steer clear of spirulina products.
It is also not recommended to take spirulina alongside B12 supplements, as the analogues in the spirulina can hinder B12 absorption. Spirulina products are, for this reason, no longer allowed to be advertised as B12 sources (7).
AFA Algae (Aphanizomenon flos-aquae)
AFA algae has very similar properties to spirulina; its previously measured B12 content has now been proven to be pseudo B12 and thus this alga is no longer considered a B12 supply (8). One study on AFA, which is still frequently cited, attempted to measure the effect of the alga through testing B12 blood serum levels and homocysteine levels. Both of these tests are unsuitable, however, as the serum test cannot differentiate between B12 and its analogues, whilst the homocysteine test is also influenced by levels of folate and vitamin B6 (9). Exact chemical measurements have shown that this alga simply contains ineffective analogues.
Nori – Still in Question
One potential source that is still being debated is the red algae nori (porphyra). Some studies have identified its content as B12 analogues (6), whilst others have come to the conclusion that the B12 which is measured in the fresh alga is destroyed during the drying process. It has also been demonstrated that eating dried nori actually worsened the vitamin B12 status in the body (10).
On the other hand, some studies have shown that nori contains large quantities of genuine vitamin B12 (11, 12) and that it had a clear biological effect when tested on rats (13).
The aforementioned results regarding nori are still widely disputed and have mostly been interpreted as an indication that, since the vitamin B12 and analogue content varies so much from test to test, no clear statement can be made on nori as a B12 source. Using this information, nori cannot be considered a reliable source of the vitamin, as it is not possible for the consumer to check the B12 content of each specific product.
Chlorella – Currently the Best Candidate
Out of all the potential plant sources of B12, chlorella is the most promising at present. Yet even here there are also contradictory studies: whilst the first American study carried out in 1968 could not prove any B12 content in chlorella whatsoever (14); current studies show it to have a high B12 content and low levels of analogues (15, 16).
One theory to explain this difference is that many commercial chlorella products are grown under sterile conditions, not conducive to the production of the microorganisms necessary for B12 to develop. Others assume that the first study simply failed on account of its now outdated testing methods.
At present, there is no evidence to suggest that chlorella can cure a B12 deficiency, because no such study has been carried out; further research is required to scientifically prove the B12 content in this alga. Even so, it certainly seems to be the best candidate for a vegan source of B12.
Chlorella: Vitamin B12 Content
The vitamin B12 content in chlorella does vary slightly across studies. The average content can be estimated between 80 – 100 µg per 100g according to current studies. In consideration of the absorption mechanism of B12, ideally three grams of chlorella – the equivalent of a teaspoon/roughly six tablets – taken in the morning and evening should cover the body’s daily requirement.
This is however a significantly more expensive alternative to B12 supplements; chlorella products are around five times the price of conventional B12 supplements, although they do also include other important nutrients such as protein, vitamin D and chlorophyll.
Price comparison between chlorella and B12 supplements:
Total B12 Content
50 000 µg
Chlorella powder (organic)
10 000 µg
Chlorella tablets (organic)
12 000 µg
*Based on the prices of affordable products found online
For Whom is Chlorella Suitable?
The B12 content of chlorella might be very high for a plant, but it is still considered quite low overall. A supply of B12 from this alga alone will only suffice if your health and lifestyle matches the following description:
- Very good health
- Optimal absorption rate
- Very low B12 requirement (no stress, no disease)
- Several doses of chlorella per day
A sensible option would be to take chlorella alongside a B12 supplement, so that the alga is not being relied upon to cover 100% of the daily requirement. In addition to these two sources, fortified foods – such as vegan milks, juices and other products – can also be consumed to add further small doses of B12.
Plant-Based, Vegan Vitamin B12
For those who are urgently seeking a plant-based source of vitamin B12, chlorella is the best current option. Whether this alga is better than regular vegan B12 supplements however is still a matter of debate. Provided that supplements contain natural forms of hydroxocobalamin and methylcobalamin, they can be considered identical to natural sources – even if the active ingredients have been chemically isolated.
The low content of B12 in chlorella unfortunately makes it impractical as the sole source of B12 for many people. Even slight absorption difficulties increase the B12 requirement by a considerable amount.
Algae are best consumed as part of a diet, which contains multiple sources of B12, such as enriched vegan products. As a result, the body’s B12 intake can be spread evenly over the course of day, allowing the body’s B12 absorption mechanism via intrinsic factor (IF) to work optimally. IF allows for around 2 µg per meal/snack to be absorbed.
- V. Herbert, G. Drivas: Spirulina and vitamin B12. JAMA, 1982, 248(23), 3096-7
- F. Watanabe, H. Katsura, S. Takenaka, T. Fujita, K. Abe, Y. Tamura, T. Nakatsuka, Y. Nakano: Pseudovitamin B12 is the predominate cobamide of an algal health food, spirulina tablets. J Agric Food Chem, 1999, 47, 4736–4741
- H. van den Berg, L. Brandson, B. J. Sinkeldam: Vitamin B12 content and bioavailability of spirulina and nori in rats. Journal of Nutritional Biochemistry, 1991, 2(6), 314-318
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- OLG Hamm, Urteil vom 17. August 2010, Az. I-4 U31/10
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- Baroni, Luciana, et al. Effect of a Klamath algae product (“AFA-B12”) on blood levels of vitamin B12 and homocysteine in vegan subjects: a pilot study. International journal for vitamin and nutrition research, 2009, 79. Jg., Nr. 2, S. 117-123.
- Yamada K, Yamada Y, Fukuda M, Yamada S. Bioavailability of dried asakusanori (porphyra tenera) as a source of Cobalamin (Vitamin B12). Int J Vitam Nutr Res. 1999 Nov;69(6):412-8
- F. Watanabe, S. Takenaka, H. Katsura, S. A. Masumder, K. Abe, Y. Tamura, Y. Nakano: Dried green and purple lavers (Nori) contain substantial amounts of biologically active vitamin B12 but less of dietary iodine relative to other edible seaweeds. J Agric Food Chem, 1999, 47(6), 2341-3
- F. Watanabe, Y. Yabuta, T. Bito, F. Teng: Vitamin B12-Containing Plant Food Sources for Vegetarians. Nutrients, 2014, 6, 1861-1873
- Takenaka S, Sugiyama S, Ebara S, Miyamoto E, Abe K, Tamura Y, Watanabe F, Tsuyama S, Nakano Y. Feeding dried purple laver (nori) to vitamin B12-deficient rats significantly improves vitamin B12 status. Br J Nutr. 2001 Jun;85(6):699-703. PubMed PMID: 11430774.
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