Spirulina: what it is and how it works

Spirulina is often called a "superfood" and "the alga of the future." It is sold as a powder, in tablets, and as a coloring for smoothies. The editorial team explains what spirulina actually is, what it is made of, which mechanisms of action are supported by research, and where the science ends and the marketing begins.

What spirulina is

Spirulina is the general trade name for the dried biomass of cyanobacteria of the genus Arthrospira, primarily the species Arthrospira platensis and Arthrospira maxima. Despite the common name "blue-green alga," from a biological standpoint it is not an alga but a photosynthetic bacterium. It got its name from the spiral shape of the filaments visible under a microscope.

In nature, spirulina grows in warm alkaline lakes. Historically it was harvested and eaten in the area of Lake Chad in Africa and in the Valley of Mexico. Today most spirulina is grown under controlled conditions — in open ponds or closed photobioreactors.

After cultivation the biomass is filtered, washed, and dried, producing a dark green powder with a characteristic "marine" smell. From it, tablets, capsules, and also extracts of individual components — for example, the pigment phycocyanin — are made.

It is important not to confuse spirulina with chlorella — a green microalga that is a true plant cell with a hard cell wall. These products are often sold side by side, but they have different composition and properties.

Composition: protein, pigments, micronutrients

Spirulina is known for its high protein content — according to various sources, it makes up 50 to 70% of the dry weight. However, this figure impresses only as a percentage: a normal serving of the supplement is a few grams, so the real contribution to the daily protein requirement is small. For comparison, 5 g of spirulina will provide about 3 g of protein.

The most interesting component from a pharmacological standpoint is phycocyanin — a blue pigment-protein that takes part in photosynthesis. It is with this that most of the antioxidant and anti-inflammatory effects described in experimental studies are associated. Spirulina also contains chlorophyll, beta-carotene and other carotenoids, gamma-linolenic acid, and iron.

Vitamin B12 deserves a separate mention. Spirulina was long advertised as a source of B12 for vegans, but studies summarized in Watanabe's review (2007) showed that most of the "B12" in it is pseudo-vitamin B12, inactive for humans. Therefore spirulina cannot be relied on as a source of this vitamin.

The composition of spirulina can differ substantially depending on the strain, the growing conditions, and the processing, so the figures on the labels of different manufacturers do not always match.

Mechanisms of action

Most of spirulina's mechanisms of action have been studied in cell cultures and animals. In such models, phycocyanin shows antioxidant properties, binding free radicals, and inhibits some inflammatory pathways. There are data on effects on the activity of antioxidant defense enzymes.

In humans, the effect on the lipid profile has been best studied. A meta-analysis by Serban and colleagues (2016) showed that taking spirulina was associated with a reduction in total cholesterol, LDL, and triglycerides and an increase in HDL, though the studies were small and heterogeneous.

For athletes, the main interest is the antioxidant effect: intense exercise increases the formation of reactive oxygen species, and in theory spirulina could reduce oxidative stress and muscle damage. Small studies, for example by Lu and colleagues (2006) and Kalafati and colleagues (2010), provide some support for this hypothesis. We examine the evidence base in detail in a separate article.

It is worth remembering that antioxidants are not always beneficial for training adaptation: part of oxidative stress is a signal for the body to adapt. So "more antioxidants" does not automatically mean "a better result."

Use and practical aspects

In human studies, doses of 1 to 10 g of spirulina per day were usually used, most often a few grams over several weeks. In studies on athletes, the dose was about 6–7.5 g per day.

Spirulina can be added to smoothies, juices, and yogurts or taken in tablets. The powder has a specific taste, so many people choose the tablet form. For better tolerance, intake begins with smaller doses, gradually increasing to the desired amount.

• Powder— cheaper per gram, convenient for smoothies.
• Tablets and capsules— tasteless, but for a few grams you need many units.
• Phycocyanin extract— a concentrated pigment, also used as a food coloring.

As a source of protein, spirulina is impractical: to get a serving comparable to a protein shake, you would have to eat tens of grams, which is unpleasant in taste and expensive. Its role is more that of a functional supplement than a dietary staple.

Realistic expectations are small changes in individual health indicators, not a noticeable improvement in athletic performance.

Safety and quality

The United States Pharmacopeia (USP) conducted a safety assessment of spirulina and concluded that, on the whole, it does not pose serious health risks provided the product is of proper quality (Marles et al., 2011). The main risks are related not to spirulina itself but to contamination.

The best-known threat is microcystins, toxins produced by other cyanobacteria that can get into the culture when grown in open bodies of water. Gilroy and colleagues (2000) detected microcystins in some blue-green algae supplements, especially those based on Aphanizomenon flos-aquae. Contamination with heavy metals is also possible.

Spirulina contains phenylalanine, so it is contraindicated for people with phenylketonuria. People with autoimmune diseases, as well as those taking immunosuppressants or anticoagulants, should consult a doctor because of a theoretical effect on immunity and blood clotting.

During pregnancy, breastfeeding, and for children, there are insufficient reliable data on safety, so in these situations the supplement should be taken only on a doctor's recommendation.

Editorial conclusions

Spirulina is the dried biomass of Arthrospira cyanobacteria with a high percentage of protein, the pigment phycocyanin, carotenoids, and iron, but it is not a reliable source of vitamin B12.

Its moderate effect on the lipid profile is best supported in humans; the antioxidant effects for athletes have a limited, though interesting, evidence base.

The key to safe use is product quality: choose spirulina from manufacturers with laboratory testing for microcystins and heavy metals.

We also recommend reading our articles "The benefits of spirulina for athletes: the evidence base," as well as materials on antioxidants in sport and on vitamin B12 in a vegan diet.

References

1. Marles RJ, Barrett ML, Barnes J, et al. United States Pharmacopeia safety evaluation of spirulina. Crit Rev Food Sci Nutr. 2011;51(7):593–604.
2. Watanabe F. Vitamin B12 sources and bioavailability. Exp Biol Med (Maywood). 2007;232(10):1266–1274.
3. Serban MC, Sahebkar A, Dragan S, et al. A systematic review and meta-analysis of the impact of Spirulina supplementation on plasma lipid concentrations. Clin Nutr. 2016;35(4):842–851.
4. Kalafati M, Jamurtas AZ, Nikolaidis MG, et al. Ergogenic and antioxidant effects of spirulina supplementation in humans. Med Sci Sports Exerc. 2010;42(1):142–151.
5. Lu HK, Hsieh CC, Hsu JJ, Yang YK, Chou HN. Preventive effects of Spirulina platensis on skeletal muscle damage under exercise-induced oxidative stress. Eur J Appl Physiol. 2006;98(2):220–226.
6. Gilroy DJ, Kauffman KW, Hall RA, Huang X, Chu FS. Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environ Health Perspect. 2000;108(5):435–439.
7. Karkos PD, Leong SC, Karkos CD, Sivaji N, Assimakopoulos DA. Spirulina in clinical practice: evidence-based human applications. Evid Based Complement Alternat Med. 2011;2011:531053.