Benefits of Chlorella for Athletes: The Evidence
Chlorella, a single-celled freshwater alga, has moved from health-food shops into the kit bags of runners, cyclists and gym-goers. Labels promise better stamina, faster recovery and a nutrient boost for plant-based diets. Our editorial team looked past the marketing to see which of these claims rest on controlled human research and which are extrapolated from test tubes and animals.
What chlorella actually is
Chlorella is a genus of green microalgae, with Chlorella vulgaris and Chlorella pyrenoidosa being the species most often found in supplements. Each cell is only a few micrometres across and is surrounded by a tough cellulose-rich wall. Because humans cannot digest that wall well, commercial products are usually described as "broken cell wall" chlorella, meaning the cells have been mechanically cracked to improve absorption of their contents.
On a dry-weight basis chlorella is rich in protein, chlorophyll, carotenoids such as lutein, and several minerals. It also contains a fraction marketed as "chlorella growth factor", a loosely defined extract of nucleotides and peptides. That last term has no agreed scientific definition, which is worth remembering when it appears prominently on packaging.
It is important not to confuse chlorella with spirulina. Spirulina is technically a cyanobacterium rather than a true alga, it has a softer cell wall and a different nutrient profile. The two are often sold together, but studies on one cannot simply be applied to the other.
In the UK and the wider EU, chlorella is treated as a food ingredient with a history of consumption, so it can be sold as a food supplement without novel-food authorisation. That status says nothing about effectiveness; it simply means the product falls under general food law rather than medicines regulation, and no health claims about athletic performance have been authorised for it.
Endurance and aerobic capacity
The most frequently quoted performance study is a small Japanese trial by Umemoto and Otsuki published in 2014. Young, healthy participants took a chlorella-based multicomponent supplement for four weeks in a double-blind crossover design, and their peak oxygen uptake during a cycle test increased compared with placebo. The authors suggested that improved oxygen delivery to muscles might explain the effect.
The study is interesting but limited. It involved only around a dozen participants, they were not trained athletes, and the product contained other ingredients alongside chlorella. A single small trial of this kind can generate a hypothesis; it cannot establish that chlorella reliably improves endurance in a club cyclist or a semi-professional footballer.
The same research group reported that a similar supplement reduced arterial stiffness in healthy young men. Arterial compliance is relevant to cardiovascular health, but a change in a vascular marker does not automatically translate into faster race times. Independent replication by other laboratories, ideally in trained populations, is still lacking.
No controlled trials have shown that chlorella increases muscle strength, muscle mass or sprint performance. Claims along those lines are generally borrowed from its protein content, but the amounts consumed in typical servings of a few grams contribute very little protein to an athlete's daily total.
Recovery, immunity and cardiovascular markers
Heavy training can temporarily depress some aspects of immune function, which is why immune support is a common selling point. Small studies have reported changes in salivary immunoglobulin A and in natural killer cell activity after chlorella supplementation, but these have mostly involved non-athletes and short follow-up periods. None has convincingly shown fewer infections or lost training days.
The strongest body of human data relates to cardiometabolic risk factors. A meta-analysis by Fallah and colleagues (2018) pooled randomised controlled trials and found modest reductions in total cholesterol, LDL cholesterol and blood pressure with chlorella compared with control. These populations were largely adults with elevated risk rather than athletes, so the relevance to a healthy, active person is uncertain.
An earlier review by Merchant and Andre summarised trials in fibromyalgia, hypertension and ulcerative colitis. The results were mixed and many studies were small or uncontrolled, but they helped establish that daily intakes of several grams were generally well tolerated over months.
For recovery from muscle damage specifically, the evidence is close to non-existent. If your goal is to bounce back faster between sessions, sleep, total energy intake, carbohydrate and protein timing will have far more impact than any algae supplement.
Nutrient density: iron, B12 and protein
Chlorella is frequently promoted to vegans and vegetarians as a source of vitamin B12 and iron, two nutrients that are genuinely important for endurance athletes. The picture here is more nuanced than labels suggest. Analytical work reviewed by Watanabe and colleagues showed that some chlorella products contain biologically active B12, while others contain inactive analogues that do not support human metabolism.
Because B12 content varies so much between batches and brands, chlorella should not be relied upon as the sole B12 source for anyone following a plant-based diet. A dedicated, standardised B12 supplement or fortified foods remain the safer strategy, with blood monitoring where deficiency is suspected.
| Nutrient | Presence in chlorella | Practical relevance for athletes |
|---|---|---|
| Protein | High per 100 g dry weight | Negligible at typical 2–5 g servings |
| Vitamin B12 | Variable, partly inactive analogues | Not a reliable sole source |
| Iron | Present, amount varies | May contribute; not a treatment for deficiency |
| Vitamin K | Can be substantial | Relevant for people on warfarin |
| Iodine | Usually low, but variable | Check labels if you have thyroid disease |
Iron is a similar story. Chlorella does contain iron, but endurance athletes with confirmed iron deficiency, especially female runners, need a diagnosis and a structured plan agreed with a clinician rather than a green powder. Ferritin and full blood count results should guide that decision.
The protein content looks impressive on a per-100-gram basis, but nobody eats 100 grams of chlorella. A typical daily serving of three grams provides roughly two grams of protein, which is trivial next to the 1.2–2.0 g per kilogram of body weight that sports nutrition bodies commonly suggest for active people.
Safety, interactions and quality in the UK
At intakes used in trials, chlorella is generally well tolerated. The most common complaints are digestive: bloating, loose stools, green-coloured faeces and nausea, particularly in the first week. Starting with a small amount and building up gradually tends to reduce these effects.
There are some specific cautions worth knowing:
- Anticoagulants: chlorella can contain meaningful vitamin K, which may reduce the effect of warfarin. Anyone on anticoagulants should speak to their GP or anticoagulation clinic first.
- Immunosuppression: because of its proposed immune-stimulating effects, people on immunosuppressive medication should seek medical advice.
- Allergy and photosensitivity: rare allergic reactions and skin sensitivity to sunlight have been reported.
- Pregnancy and breastfeeding: safety data are insufficient, so routine use is not recommended.
Quality is a real concern. Algae grown in open ponds can absorb heavy metals or become contaminated with other microorganisms. Look for products whose manufacturers publish independent laboratory analyses, and for athletes in tested sport, batch-tested certification schemes reduce the risk of inadvertent contamination with prohibited substances.
Finally, remember that in Great Britain food supplements are not pre-approved for efficacy. Enforcement relies on trading standards and the Food Standards Agency, so the presence of a product on a shelf is not evidence that its performance claims have been verified.
Conclusions of the editorial team
Chlorella is a nutrient-dense alga with a reasonable safety record, and there is moderate evidence for small improvements in cholesterol and blood pressure in at-risk adults. For athletic performance, however, the data consist of a handful of small studies, often using multi-ingredient products.
It should not be treated as a reliable source of vitamin B12, iron or protein. Athletes with genuine deficiencies need diagnosis and targeted treatment, not a superfood with variable composition.
If you enjoy chlorella and tolerate it well, there is little harm in using it as part of a varied diet, provided you choose a tested product and check for interactions. Just keep expectations realistic.
For further reading, our editorial team suggests our articles on vitamin B12 forms and how to choose one, iron status in endurance athletes, and how to interpret systematic reviews of supplements.
References
- Umemoto S, Otsuki T. Chlorella-derived multicomponent supplementation increases aerobic endurance capacity in young individuals. J Clin Biochem Nutr. 2014;55(2):143–146.
- Otsuki T, Shimizu K, Iemitsu M, Kono I. Multicomponent supplement containing Chlorella decreases arterial stiffness in healthy young men. J Clin Biochem Nutr. 2013;53(3):166–169.
- Fallah AA, Sarmast E, Habibian Dehkordi S, et al. Effect of Chlorella supplementation on cardiovascular risk factors: a meta-analysis of randomized controlled trials. Clin Nutr. 2018;37(6 Pt A):1892–1901.
- 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.
- Watanabe F, Yabuta Y, Bito T, Teng F. Vitamin B12-containing plant food sources for vegetarians. Nutrients. 2014;6(5):1861–1873.
- Panahi Y, Darvishi B, Jowzi N, et al. Chlorella vulgaris: a multifunctional dietary supplement with diverse medicinal properties. Curr Pharm Des. 2016;22(2):164–173.
