Chlorella Benefits for Athletes: The Evidence Base

Chlorella is increasingly advertised as a supplement for athletes: “increases endurance,” “strengthens immunity during hard training,” “speeds up recovery.” The editors have analyzed which clinical studies stand behind these claims, how good they are, and what of them can realistically be transferred to training practice.

Why chlorella is of interest for sport

Intense training creates several challenges for the body: oxidative stress, temporary suppression of immune defense, an increased need for micronutrients. Theoretically, chlorella may affect each of these aspects thanks to antioxidant pigments, immunoactive polysaccharides, and its content of iron, folate, and B vitamins.

The topic of immunity is especially relevant. It is known that periods of high load are accompanied by a decline in some indicators of mucosal immunity, in particular secretory immunoglobulin A in saliva, and in some athletes by an increase in the frequency of upper respiratory tract infections.

The second hypothesis concerns aerobic performance: if a supplement improves vascular function or oxygen delivery, this could be reflected in maximal oxygen uptake (VO2max) and endurance.

However, there is a distance between a hypothesis and a proven effect. Below we examine specific studies and then assess their strengths and weaknesses.

Aerobic endurance: VO2peak studies

The most frequently cited work is Umemoto and Otsuki (2014), published inJournal of Clinical Biochemistry and Nutrition. Young participants received a chlorella-based supplement or placebo over 4 weeks in a double-blind crossover design.

After the chlorella course, peak oxygen uptake (VO2peak) increased, whereas on placebo there were no significant changes. The authors suggested that the effect may be related to an improvement in oxygen-transport function, but the mechanism remained undetermined.

It is important to assess the limitations: the sample numbered only a few dozen people, the participants were not highly trained athletes, and the supplement itself was “multi-component” based on chlorella. No direct tests of athletic performance (time over a distance, power) were conducted.

This same research group studied the effect of chlorella on arterial stiffness and nitric oxide production in middle-aged and older people. The results are consistent with the hypothesis of a vascular mechanism but concern a different population.

Immunity during hard training

The study by Otsuki et al. (2012) inNutrition Journalwas conducted on participants of an intensive kendo training camp. During the camp, in the group without chlorella the level of secretory IgA in saliva declined, whereas in the group receiving chlorella this decline was less pronounced.

SIgA is the first line of defense of the mucous membranes against viruses and bacteria, so the result looks practically significant. However, the authors did not measure the frequency of illness, so it is unknown whether the change in the marker translated into fewer colds.

Kwak et al. (2012), in a randomized placebo-controlled study in healthy adults (not athletes), showed that 8 weeks of taking chlorella increased the activity of natural killer cells. This supports the general immunomodulatory hypothesis, although the population is not a sporting one.

Together these works give a signal that chlorella may support certain immune indicators, but recommendations for athletes require studies with clinical endpoints — the number of missed training sessions and episodes of infection.

Limitations of the evidence base

The editors highlight several systemic problems in chlorella research in the sports context. First, small samples: most works include dozens of participants, which makes the results sensitive to chance.

Second, the heterogeneity of products: different species and strains of chlorella, different methods of cell wall breakdown, different doses, and “multi-component” supplements. The result of one product cannot automatically be transferred to another.

Third, a significant part of the research has been conducted by a small number of research groups, mostly in Japan and Korea, including with manufacturer support. This does not make the results false, but it does require independent replications.

• few studies on trained high-level athletes;
• surrogate markers (VO2peak, SIgA) predominate instead of real performance;
• short observation periods;
• the absence of meta-analyses specifically for sports endpoints.

Fourth, there are no data on chlorella's superiority over an ordinary balanced diet with sufficient fruit, vegetables, and protein. For an athlete with a diet free of deficiencies, the additional benefit may be minimal.

What this means in practice

Chlorella is not among the supplements with a strong evidence base for sports performance, such as creatine, caffeine, or beta-alanine. Its place is in the category of “possibly useful” products with mostly preliminary data.

If an athlete wants to try chlorella, the logical context is periods of intensive training camps or competitions, when it is important to support immunity. In studies, courses lasting several weeks were used.

The risks should be taken into account: interaction with warfarin due to vitamin K, possible photosensitivity, gastrointestinal complaints, and product quality. For athletes undergoing doping control, it is important to choose products certified free of prohibited substances, since any supplement carries a risk of contamination.

Chlorella is not on the WADA Prohibited List, but the mere fact of its legality does not guarantee the “purity” of a specific product.

Editors' conclusions

The evidence base for chlorella's benefits for athletes is limited to a few small studies: there are signals regarding VO2peak, secretory IgA, and NK cell activity.

None of the studies showed an improvement in real athletic performance, and most works have small samples and heterogeneous products.

Chlorella can be regarded as a supplementary rather than a basic tool, primarily during periods of high load, and only after nutrition and sleep have been sorted out.

We also recommend reading “Chlorella: What It Is and How It Works,” “How to Take Chlorella: Dosage, Timing, Duration,” and “Chlorella Side Effects.”

References

1. Umemoto S, Otsuki T. Chlorella-derived multicomponent supplementation increases aerobic endurance capacity in young individuals. J Clin Biochem Nutr. 2014;55(2):143–146.
2. Otsuki T, Shimizu K, Iemitsu M, Kono I. Chlorella intake attenuates reduced salivary SIgA secretion in kendo training camp participants. Nutr J. 2012;11:103.
3. Kwak JH, Baek SH, Woo Y, et al. Beneficial immunostimulatory effect of short-term Chlorella supplementation: enhancement of natural killer cell activity and early inflammatory response (randomized, double-blinded, placebo-controlled trial). Nutr J. 2012;11:53.
4. Bito T, Okumura E, Fujishima M, Watanabe F. Potential of Chlorella as a dietary supplement to promote human health. Nutrients. 2020;12(9):2524.
5. Panahi Y, Darvishi B, Jowzi N, Beiraghdar F, Sahebkar A. Chlorella vulgaris: a multifunctional dietary supplement with diverse medicinal properties. Curr Pharm Des. 2016;22(2):164–173.
6. Merchant RE, Andre CA. A review of recent clinical trials of the nutritional supplement Chlorella pyrenoidosa in the treatment of fibromyalgia, hypertension, and ulcerative colitis. Altern Ther Health Med. 2001;7(3):79–91.
7. World Anti-Doping Agency. The World Anti-Doping Code International Standard: Prohibited List. Montreal: WADA; оновлюється щорічно.