The Benefits of Spirulina for Athletes: The Evidence Base

Spirulina is actively marketed as a supplement for endurance and faster recovery. But how much research stands behind these promises, and how convincing is it? The editorial team examined the key studies on athletes and physically active people and assessed the real level of evidence.

Where the hypothesis came from

Sports science’s interest in spirulina is based on its composition. Phycocyanin and carotenoids have antioxidant properties in laboratory models, and intense training increases the formation of reactive oxygen species. Hence a logical hypothesis: spirulina may reduce oxidative stress, muscle damage, and fatigue.

A second line of reasoning is related to the iron content: theoretically, spirulina may support blood formation and the oxygen capacity of the blood, which is important for endurance sports. A third is related to a potential effect on the use of fats as an energy source.

However, there is a large distance between a hypothesis and a proven effect in humans. So the key question is which studies exactly have been conducted on athletes, on how many participants, and with what results.

It is also important to remember the principle: an effect on biochemical markers (for example, the level of oxidation products in the blood) does not yet mean an improvement in athletic performance. We will consider both types of results separately.

• Markers of oxidative stress — show biochemical changes but not the result.
• Markers of muscle damage — related to recovery.
• Performance indicators — time to exhaustion, oxygen consumption, strength.
• Subjective indicators — the feeling of fatigue, the quality of recovery.

Endurance and energy metabolism

The most frequently cited work is the study by Kalafati et al. (2010), published in Medicine & Science in Sports & Exercise. Moderately trained men received 6 g of spirulina per day or a placebo for 4 weeks in a crossover design, after which they performed a two-hour run of moderate intensity followed by a run to exhaustion.

In this study, after taking spirulina the time to exhaustion in the final run was longer, and fat oxidation during exercise was higher, than after placebo. The authors also reported favorable changes in the level of glutathione — one of the key intracellular antioxidants.

Despite the interesting results, the study had limitations: a small number of participants (fewer than ten) and a specific exercise protocol. Such data can be considered preliminary rather than definitive proof of effectiveness.

There are so far not enough repeat large studies that would confirm an improvement in endurance in trained athletes. So the claim “spirulina increases endurance” should be regarded as a hypothesis with some support rather than as an established fact.

Oxidative stress and muscle damage

Lu et al. (2006) studied the effect of spirulina on markers of muscle damage in untrained young people. The participants received 7.5 g of spirulina per day for three weeks, after which they performed exercise on a treadmill to exhaustion.

In the spirulina group, the level of malondialdehyde — a marker of lipid peroxidation — rose less after exercise than on placebo, and the activity of some antioxidant enzymes was higher. The authors also reported an increase in the time to exhaustion.

These results are consistent with the hypothesis of an antioxidant effect, but again they were obtained on small samples of untrained people. In trained athletes, the body’s own antioxidant system is usually more efficient, so the effect of the supplement may be smaller.

In addition, a reduction in oxidative stress is not always desirable. Studies with high doses of vitamins C and E showed that excessive suppression of oxidative signals can weaken some training adaptations. For spirulina such effects have not been studied, which is another reason for caution in interpretation.

Oxygen metabolism and hematological indicators

A small study by Gurney and Spendiff (2020) assessed the effect of a short course of spirulina on indicators during exercise on an arm cycle ergometer. The authors reported an improvement in oxygen consumption and changes in hemoglobin compared with placebo. However, the sample was small and the exercise specific, so transferring the conclusions to runners or cyclists is premature.

The hypothesis of support for blood formation rests on the iron content in spirulina. For people with iron deficiency, any additional source may be useful, yet the standard of treatment for iron deficiency remains iron preparations under a doctor’s supervision, not spirulina.

Systematic reviews that consider spirulina in sport generally acknowledge the promise of individual results but emphasize the small number of high-quality studies. Spirulina is not on the list of supplements with a strong evidence base in the IOC consensus on dietary supplements for high-level athletes.

Thus, for now the data on oxygen metabolism and blood formation should be considered preliminary.

Limitations of the studies and practical conclusions

The main problem of the evidence base is small samples. Most studies included only a few dozen, or even fewer, participants, which raises the risk of random results and exaggeration of the effect.

The second problem is heterogeneity: different doses, durations, populations (from untrained students to moderately trained athletes), and exercise protocols. Because of this it is hard to compare the results with each other and make generalizations.

The third is that the quality and composition of the supplements in different studies could differ, and the phycocyanin content was usually not standardized. So even a positive result is hard to transfer to a product from a store shelf.

Practical conclusion: spirulina can be a reasonable addition to the diet for people who like this product and who choose quality raw material, but one should not count on a noticeable improvement in athletic performance. Investing in supplements with a strong evidence base, such as creatine or caffeine, or in sleep and nutrition, will give a greater effect.

Editorial Conclusions

Studies of spirulina in people who train show interesting signals: a reduction in markers of oxidative stress, an increase in the time to exhaustion, changes in oxygen metabolism.

However, these data were obtained in small and heterogeneous studies, and large independent trials on trained athletes are so far lacking.

Spirulina can be regarded as a supplementary rather than a key supplement: realistic expectations and the choice of a quality product with control for microcystins and heavy metals are mandatory conditions.

We also advise reading our articles “Spirulina: What It Is and How It Works”, as well as materials on antioxidants and training adaptation and on the supplements with the strongest evidence base in sport.

References

1. 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.
2. 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.
3. Gurney T, Spendiff O. Spirulina supplementation improves oxygen uptake in arm cycling exercise. Eur J Appl Physiol. 2020.
4. Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.
5. 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.
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.