Also known as: Arthrospira platensis, Blue-green algae, Phycocyanin, Spirulina platensis
FoundationalGood evidence
A blue-green algae cultivated as a food, unusually high in protein and rich in phycocyanin. Genuinely nutritious, and one where where it was grown matters more than almost any other ingredient here.
Typical dose
1.0–8.0 g per day
Any time, with or without food
What it is
Spirulina is a cyanobacterium, commonly called blue-green algae, cultivated commercially in shallow ponds. It has a long history as a food, harvested from lakes in Mexico and Chad well before it became a supplement.
By dry weight it is around 60 to 70 per cent protein, which is exceptional for a plant-type food, and it supplies a complete amino acid profile. In practice, though, serving sizes are small enough that its protein contribution is modest — a 5 g serving supplies roughly 3 g of protein, which is not a meaningful protein source however impressive the percentage sounds.
Phycocyanin is the blue pigment that gives spirulina its colour and much of its studied activity. It is also used as a natural food colouring.
How it works
Phycocyanin has antioxidant activity and effects on inflammatory signalling, and is the compound credited with most of spirulina's studied effects beyond simple nutrition.
Spirulina also supplies iron, B vitamins and gamma-linolenic acid, alongside its protein content, so part of what it does is straightforwardly nutritional rather than pharmacological.
One point worth correcting: spirulina contains B12 analogues rather than active B12. These are not usable by humans and may even compete with the real thing. Spirulina is not a B12 source for anyone eating a plant-based diet, despite being marketed that way for years.
What the evidence shows
Lipid markers are the best-studied area, with meta-analyses reporting modest improvements in cholesterol and triglyceride measures across a number of trials.
There is a smaller literature on blood pressure and on exercise-related outcomes, including a few trials reporting improvements in endurance measures and reduced markers of exercise-induced muscle damage. Sample sizes are small.
Overall the evidence is reasonable for a food-type supplement, though effect sizes are modest and trials are generally small. It is better understood as a nutrient-dense food than as an active supplement.
Dosing
Common intake is 1-8 g daily, with most trials using 2-8 g. Higher doses are used in the lipid research.
Spirulina has a strong, distinctly marine taste that many people find difficult in water. Blending it into a smoothie with something sweet and acidic works considerably better than mixing it plain.
The most important buying consideration is not dose but source. Spirulina grown in poorly controlled open ponds can accumulate heavy metals from the water, and can be contaminated with other cyanobacteria that produce genuinely harmful toxins. Buy from a producer that tests for both, and treat any product without published testing as unquantifiable.
At a glance
Common forms
Spirulina powder, Tablets, Phycocyanin extract, Within greens blends
Half-life / duration
Not applicable; effects on markers accrue over weeks
Timing
Any time, with or without food
Competition status
Permitted — not on the WADA Prohibited List
Category
Foundational
Safety and side effects
Properly produced spirulina is well tolerated, with digestive upset and, occasionally, headache the main reported effects. Green discolouration of stools is common and harmless.
Contamination is the genuine risk, and it is specific to how spirulina is grown. Open ponds can accumulate heavy metals, and other cyanobacteria growing alongside it can produce toxins that place a real load on the liver. Documented problems have traced back to poorly controlled production rather than to spirulina itself.
Because it has immune-modulating activity, speak to your doctor before use if your immune system is being managed. It also contains phenylalanine, which matters to anyone advised to restrict specific amino acids.
Who should avoid it
Buy only from producers who test for heavy metals and cyanobacterial toxins, and treat untested products as unquantifiable. Avoid if you have been advised to restrict specific amino acids, since spirulina contains phenylalanine. Speak to your doctor before use if your immune system is being managed or if you take regular medication. Not a source of usable B12.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
