Spirulina for athletes: what does the evidence show?
Spirulina is promoted as a protein-rich superfood for active people. Our editorial team reviewed the controlled trials on endurance, recovery and blood markers and explains where the evidence is solid, where it is thin and what to watch for in terms of quality.
What spirulina is
Spirulina is the common name for dried biomass of cyanobacteria, mainly Arthrospira platensis and Arthrospira maxima. Although often called an "alga", it is technically a photosynthetic bacterium. It has been harvested from alkaline lakes for centuries and is now cultivated commercially in open ponds and closed systems.
By dry weight, spirulina is roughly 55–70% protein, and it also contains B vitamins, iron, beta-carotene, gamma-linolenic acid and the blue pigment phycocyanin, which is responsible for much of its antioxidant activity in laboratory studies. These figures make it sound like a superfood, but servings are small – typically a few grams – so its contribution to daily protein is modest.
For athletes, interest centres on antioxidant effects, recovery from muscle damage, oxygen uptake and blood markers. In the UK spirulina is sold as a food and food supplement, and products must comply with food safety rules, including limits on contaminants.
This article reviews what controlled human studies actually show, separating promising findings from marketing claims.
Evidence on performance and recovery
The research base is small. Many studies are short, with few participants, and some use untrained volunteers. Still, a handful of trials are frequently cited.
Kalafati and colleagues in 2010 gave moderately trained men 6 g of spirulina daily for four weeks. They reported a longer time to fatigue in a prolonged run, increased fat oxidation and improved antioxidant markers compared with placebo. Lu and co-workers in 2006 found that three weeks of spirulina reduced markers of exercise-induced oxidative stress and muscle damage in untrained students.
More recently, Gurney and Spendiff reported in 2020 that spirulina improved oxygen uptake and haemoglobin values during arm-cycling exercise. These results are interesting, but the studies involved small samples and need replication.
- Reasonably consistent: improvements in some antioxidant and oxidative-stress markers.
- Promising but limited: endurance time and oxygen uptake.
- Not shown: meaningful gains in strength or muscle mass.
A broader point applies to all antioxidants: high doses may blunt some training adaptations that rely on oxidative signalling. This has been shown mainly for high-dose vitamin C and E, and there is no evidence that spirulina has this effect, but it is a reason not to assume that "more antioxidant" is always better.
Health effects beyond performance
Spirulina has been studied for cardiovascular risk markers. A meta-analysis by Serban and colleagues in 2016 found reductions in total cholesterol, LDL cholesterol and triglycerides and an increase in HDL cholesterol. The effects were modest and the trials varied in quality.
Its iron content attracts interest from endurance athletes and plant-based eaters, who are at higher risk of low iron stores. Spirulina does contain iron, but it should not be used to self-treat iron deficiency. Low ferritin or anaemia should be investigated and treated under medical supervision.
A common misconception concerns vitamin B12. Watanabe and colleagues showed in 1999 that most of the B12-like compounds in spirulina tablets are pseudovitamin B12, which is inactive in humans. Vegans should not rely on spirulina for B12 and should use a reliable supplement or fortified foods.
Safety and quality
Spirulina is generally well tolerated, but quality is an issue. Products may be contaminated with microcystins – liver toxins produced by other cyanobacteria – or with heavy metals, depending on how and where they are grown. Roy-Lachapelle and co-workers detected cyanotoxins in several algae-based supplements.
| Concern | Who is most affected | Practical step |
|---|---|---|
| Microcystin contamination | Everyone; especially children | Choose tested products from reputable sources |
| Heavy metals | Regular users | Look for certificates of analysis |
| Phenylalanine content | People with phenylketonuria | Avoid |
| Immune stimulation | Autoimmune disease, immunosuppressants | Discuss with doctor |
| Digestive upset | New users | Start with a small serving |
Pregnant and breastfeeding women should be cautious because of the contamination risk and limited safety data. Competing athletes should prefer batch-tested products, as for any supplement.
Practical use
In studies with athletes, amounts of around 2–7.5 g per day were used for several weeks. A sensible approach for a healthy adult is to follow the label of a reputable product, starting with a lower amount to assess digestive tolerance, and to take it with meals.
Powder can be mixed into smoothies or yoghurt, while tablets are convenient but require many units to reach study amounts. The strong taste is the main reason people stop using it.
Expectations should be realistic. Spirulina is a nutrient-dense food with some promising data on oxidative stress and endurance, but it is not a substitute for adequate carbohydrate, protein and iron intake, or for structured training and sleep.
Editorial team's conclusions
Spirulina has a modest evidence base in athletes, mainly for antioxidant and muscle-damage markers, with early findings for endurance and oxygen uptake.
It is not a meaningful source of active vitamin B12 and should not replace medical treatment of iron deficiency. Benefits for lipids are small but consistent.
Product quality is the key safety issue: choose tested products and avoid unknown sources.
If you are interested in this area, see also our articles on chlorella, on iron status in endurance athletes and on antioxidants and training adaptation.
References
- 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.
- Lu HK, Hsieh CC, Hsu JJ, et al. Preventive effects of Spirulina platensis on skeletal muscle damage under exercise-induced oxidative stress. Eur J Appl Physiol. 2006;98(2):220–226.
- Gurney T, Spendiff O. Spirulina supplementation improves oxygen uptake in arm cycling exercise. Eur J Appl Physiol. 2020;120(12):2657–2664.
- 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.
- 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.
- Roy-Lachapelle A, Solliec M, Bouchard MF, Sauvé S. Detection of cyanotoxins in algae dietary supplements. Toxins (Basel). 2017;9(3):76.
