Is Spirulina a good source of vitamin B12?

Question

I've found mixed information online about using Spirulina as a source of vitamin B12 for humans when searching google for "Spiralina B12".

For instance the first match states that Spirulina has a mix of B12 analogues which are often inactive.

And the second match states: "Spirulina is a rich source of B12. Despite that, some experts believe that in B12 in spirulina is in a form that is not absorbed.

However, a 2010 study in the Journal of Agricultural and Food Chemistry found the opposite. It showed that B12 in spirulina contains 'methylcobalamin, a form of B12 of high biological activity'."

but doesn't name the study, so I can't find which study it is referring to in 2010.

Can Spirulina be used as an effective source of B12 for humans? If so how, and according to what research.

Answer 1

The Vegan Society currently advises that consuming spirulina has not been proven to prevent B12 deficiency. See their open letter on B12 which does not discuss scientific studies in detail, but gives advice based on the current evidence and consensus in nutritional science, rejecting spirulina as a possible source of B12:

Claimed sources of B12 that have been shown through direct studies of vegans to be inadequate include human gut bacteria, spirulina, dried nori, barley grass and most other seaweeds. Several studies of raw food vegans have shown that raw food offers no special protection.

Reports that B12 has been measured in a food are not enough to qualify that food as a reliable B12 source. It is difficult to distinguish true B12 from analogues that can disrupt B12 metabolism. Even if true B12 is present in a food, it may be rendered ineffective if analogues are present in comparable amounts to the true B12. There is only one reliable test for a B12 source - does it consistently prevent and correct deficiency? Anyone proposing a particular food as a B12 source should be challenged to present such evidence.

Answer 2

I can't find which study it is referring to in 2010.

Here is the 2010 paper in the Journal of Agricultural and Food Chemistry, mentioned by the OP @Ryan White.

Quantitation of methylcobalamin in a test sample of S. platensis biomass was performed using microbiological assay and chemiluminescence assay and was found to be 38.5 ± 2 and 35.7 ± 2 μg/100 g of dry biomass, respectively.

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Recommended Dietary Allowance for Vitamin B12 is 2.4 mcg for adults in the US (NIH), Daily Value is 6 mcg according to same source.

Spirulina (Arthrospira) Platensis does indeed contain B12 analogs but according to this recent paper, 5 grams of dried product could theoretically provide more than 1,7 mcg or 70% of RDA.

However, bioavailibility is still unclear when considering analogs, whatever the food source is. According to Watanabe (2007):

Vitamin B(12) bioavailability significantly decreases with increasing intake of vitamin B(12) per meal. The bioavailability of vitamin B(12) in healthy humans from fish meat, sheep meat, and chicken meat averaged 42%, 56%-89%, and 61%-66%, respectively.

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Further research is probably needed to assess bioavailability of methylcobalamin in Spirulina but recent research shows it can be a significant source of vitamin B12.