Is spirulina a B12 source if I am vegan?

No. Analysis of spirulina tablets found that 83% of what is measured as B12 is pseudovitamin B12, an analogue inactive in humans. Worse, those analogues can distort a blood test. B12 on a vegan diet is covered with a cyanocobalamin supplement.

Does spirulina improve performance?

There is one crossover trial with 6 g a day for four weeks that extended time to exhaustion and shifted fuel use towards fat. It is nine subjects: an interesting signal, not a conclusion, and it has not been replicated at scale.

Can spirulina be contaminated?

It is a real risk in the powdered algae category. In an analysis of thirteen products on the market, the microcystin positives were Aphanizomenon flos-aquae products; no spirulina tested positive, but all extracts were cytotoxic in the cell assay. That is why batch testing matters more here than in other categories.

Is it a good protein source?

It has a high protein percentage in the dry powder, but it is taken in grams, not tens of grams. A typical serving provides a few grams of protein at a price per kilo that cannot compete with any protein tub.

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Spirulina · Weak evidence

What spirulina is for and what it does

The short answer. Spirulina is a cyanobacterium sold as a superfood. There is one small, well-designed trial that found longer time to exhaustion and more fat oxidation with 6 g a day for four weeks, and it is worth knowing about, but it is nine subjects: a signal, not a conclusion. The two things worth being clear on are different. Its vitamin B12 does not work as B12 for humans. And powdered algae on the market have a contamination history that makes the batch seal matter more here than in almost any other category.

Reviews find no consistent effect. It is listed because it sells, not because it works. No figure on this page is attributed to a specific product: the effect belongs to the ingredient and every number carries its source next to it.

01 What it does and how much

Each row is a measured effect, with the figure the study gives and the source number. Where the evidence gives no figure, the column says so instead of making up a percentage.

Effects of spirulina with their source
Effect	How much	Detail
Time to exhaustion	from 2.05 to 2.70 min	After two hours of running, with 6 g a day for four weeks. The difference is significant in the trial, but it is nine moderately trained runners in a crossover design: more is needed to consider the effect established. [1]
Fat oxidation during exercise	+10.9%	With a parallel 10.3% drop in carbohydrate oxidation. It is a shift in fuel use, not a demonstrated loss of body fat. [1]
Usable vitamin B12	83% is pseudovitamin	Analysis of spirulina tablets found that the main compound is pseudovitamin B12, inactive in humans. That is why no serious guideline recommends it as a B12 source for vegan diets. [2]
Contamination of powdered algae	up to 1 µg MC-LR/g	In an analysis of thirteen algae products on the market, the ones positive for microcystins were Aphanizomenon flos-aquae, not spirulina. The practical warning is the same: in this category batch testing is not a luxury. [3]

02 How to take it

Dose. 6 g a day is the dose from the performance trial. On the market it is usually sold at 3 to 5 g.
When. In the trial it was taken daily for four weeks, with no specific time of day.
How long before you notice it. Four weeks in the only performance trial with a result.

Details that change the result

It does not count as a B12 source. On a vegan diet, B12 is covered with cyanocobalamin, not algae.
It provides protein, but 5 g of powder is about 3 g of protein: as a protein source it is extremely expensive compared with any tub in the protein category.
The batch testing seal matters more here than on a creatine tub, because it is a cultivated organism and powdered algae do have a contamination history.
With immunosuppressive treatment or an autoimmune disease, a doctor should look at this first.

03 When it makes sense and when it does not

Worth it if

As a green food within a varied diet, without expecting a specific effect.
Bought with published batch testing, which is the only thing that settles the contamination question.

Not worth it if

As a source of vitamin B12 on a vegan diet: most of what is measured is inactive pseudovitamin.
As a protein source, where the cost per gram competes with nothing.
Expecting a reliable performance improvement from a single trial with nine subjects.

04 Sources

Every figure above comes from here. They are position stands from scientific societies, meta-analyses and peer-reviewed reviews: if a claim cannot hang from one of these lines, it is not on the page. References are cited in their original form.

Kalafati M et al. Ergogenic and antioxidant effects of spirulina supplementation in humans. Med Sci Sports Exerc. 2010;42(1):142-151. Nueve varones moderadamente entrenados, diseno cruzado doble ciego, 6 g/dia durante 4 semanas: tiempo hasta el agotamiento de 2,05 a 2,70 minutos, oxidacion de hidratos -10,3 % y de grasa +10,9 %. doi:10.1249/MSS.0b013e3181ac7a45
Watanabe F, Katsura H, Takenaka S et al. Pseudovitamin B12 is the predominant cobamide of an algal health food, spirulina tablets. J Agric Food Chem. 1999;47(11):4736-4741. Los dos analogos aislados fueron pseudovitamina B12 (83 %) y vitamina B12 (17 %). doi:10.1021/jf990541b
Heussner AH, Mazija L, Fastner J, Dietrich DR. Toxin content and cytotoxicity of algal dietary supplements. Toxicol Appl Pharmacol. 2012;265(2):263-271. Trece productos de algas del mercado aleman: solo los de Aphanizomenon flos-aquae dieron positivo en microcistinas, con niveles de hasta 1 ug de equivalentes de MC-LR por gramo de peso seco; los extractos de todos los productos resultaron citotoxicos. doi:10.1016/j.taap.2012.10.005

This is not medical advice. It is what some studies say about an ingredient, not a protocol for you. With an illness, medication or pregnancy involved, the decision belongs to a healthcare professional who knows you.

Questions about spirulina

Answered with the data on this page

Is spirulina a B12 source if I am vegan?: No. Analysis of spirulina tablets found that 83% of what is measured as B12 is pseudovitamin B12, an analogue inactive in humans. Worse, those analogues can distort a blood test. B12 on a vegan diet is covered with a cyanocobalamin supplement.
Does spirulina improve performance?: There is one crossover trial with 6 g a day for four weeks that extended time to exhaustion and shifted fuel use towards fat. It is nine subjects: an interesting signal, not a conclusion, and it has not been replicated at scale.
Can spirulina be contaminated?: It is a real risk in the powdered algae category. In an analysis of thirteen products on the market, the microcystin positives were Aphanizomenon flos-aquae products; no spirulina tested positive, but all extracts were cytotoxic in the cell assay. That is why batch testing matters more here than in other categories.
Is it a good protein source?: It has a high protein percentage in the dry powder, but it is taken in grams, not tens of grams. A typical serving provides a few grams of protein at a price per kilo that cannot compete with any protein tub.

And now, which to buy

Prices, kept apart from the evidence

This page explains what spirulina does and deliberately names no brand. The comparison is the other half: 30 products from 3 stores from €0.017 per capsule, sorted by price and by how verifiable their certification is.

See the spirulina comparison

Other guides

What each supplement does, with its sources