Spirulina and chlorella: what is the difference?

Both come as green powder, both get called "superfood", and both live in the same corner of the health-food aisle. You'd expect cousins. They're closer to a bacterium and a plant that happen to be sold side by side.

Before the biology, here's the comparison that changes what you put in your basket. Say a label announces 65% protein and the serving is 2 g (four capsules). The percentage describes the powder; you eat the serving. 2 g × 0.65 is roughly 1.3 g of protein, by our arithmetic. A useful number, but nowhere near a protein shake. Hold on to that sum: it works for any algae label.

Two organisms, one shelf

Spirulina is a blue-green cyanobacterium (usually Arthrospira platensis): a bacterium that photosynthesises. Chlorella is a green alga, a single-celled organism, and several species are sold as food (C. vulgaris, C. pyrenoidosa, C. sorokiniana and others).

That difference explains most of what follows: what the powders are made of, what researchers have measured in people, and where their quality and safety questions come from. Systematic reviews of trials report small changes in blood-fat, blood-pressure and blood-sugar measures for each, but the certainty is low or very low for most outcomes. The practical differences matter more than picking a "winner".

Chlorella's green, spirulina's blue

Chlorella's colour comes from chlorophyll. Spirulina's blue-green tint includes phycocyanin.

Phycocyanin: the blue part

Phycocyanin is a water-soluble pigment-protein from cyanobacteria such as Arthrospira, and it is what makes "blue spirulina" blue. Producers usually extract it: one industry colour-manufacturers' profile describes spirulina extract as made by filtered aqueous extraction of dried Arthrospira platensis biomass, with phycocyanins as the main colouring components, and says it's typically treated as a colouring food rather than a colour additive in the EU (IACM). Phycocyanin is a delicate molecule: food-science researchers describe it as highly unstable, especially at high temperatures and under oxidative stress (Foods, 2022). That is a stability finding in a lab, not a rule for how to eat it.

What does it do in people? A lot of claims circulate about phycocyanin and inflammation, antioxidants and the brain, mostly from cell and animal studies. A 2023 systematic review of phycocyanin in diabetes found only animal and cell studies, and no human trials (Ziyaei et al., 2023, Phytomedicine). One small randomised trial (24 people, two weeks) tested a phycocyanin-rich extract (2.3 g a day) mainly for safety. It reported no change in the clotting and platelet markers it measured, lower liver enzyme (AST) levels, and reduced chronic pain scores (Jensen et al., 2016, Journal of Medicinal Food); pain is self-reported and 24 people is a small sample. So: an interesting pigment, well studied as a molecule, little tested as a human supplement.

On a label, look for the amount per serving, and for how it was measured.

How similar are they as food?

Both are protein-rich, which is the first reason people compare them. A study of commercial biomass from different producers (Muys et al., 2019) measured protein at 47 ± 8% in chlorella and 48 ± 4% in spirulina, so there was little between them on quantity. Protein quality and digestibility were lower for chlorella (digestibility 51 ± 9% against 61 ± 4%). The study also found high variability between producers, and that heavy metals, pesticides, mycotoxins and antibiotics stayed within regulatory limits, while polycyclic aromatic hydrocarbons exceeded the norm in some samples (Muys et al., 2019, Bioresource Technology). That was a sample of the 2019 market, not a verdict on any product on sale now.

Why labels say Arthrospira, Limnospira and spirulina

Names can confuse. A 2023 review of EU microalgae law notes that the commercial name "Spirulina" overlaps with an actual genus of that name, that Arthrospira platensis is the species regarded as a frequent food item, and that official lists in France, Italy and Belgium include Limnospira maxima (other Limnospira names appear only in French records), so taxonomy differs between member states (Foods, 2023). So you'll see "Arthrospira", "Limnospira" and "spirulina" on labels for what shoppers will treat as the same type of product.

What the human studies show, by outcome

Three questions help with any result: which product was tested, in whom, and what was measured. A change in a blood marker isn't the same as feeling or functioning better.

• Outcome: Cholesterol and blood fats; Spirulina: A 2023 meta-analysis of 20 studies (1,076 participants) found lower LDL, total cholesterol and triglycerides and higher HDL (Rahnama et al.). A 2025 analysis of 9 spirulina trials found no significant change in lipid measures (Pinto-Leite et al.).; Chlorella: A 2018 meta-analysis of 19 trials (797 people) found lower total and LDL cholesterol, but no significant change in triglycerides or HDL (Fallah et al.). The 2025 analysis of 12 chlorella trials found a neutral effect, while a 2026 review of 24 chlorella studies found lower LDL (-6.2 mg/dl) and total cholesterol (-8.0 mg/dl), rated very low certainty (Mardani et al.). The reviews disagree.
• Outcome: Blood pressure; Spirulina: A 2021 meta-analysis of 5 trials (230 people) reported falls in systolic and diastolic pressure, especially in people with hypertension (Machowiec et al.). The 2025 analysis found a small reduction in diastolic pressure, "of uncertain clinical significance".; Chlorella: The 2018 meta-analysis found lower blood pressure, mainly with durations of 8 weeks or more and doses above 4 g a day. The 2025 analysis found a neutral effect.
• Outcome: Blood sugar; Spirulina: A 2019 meta-analysis in people with metabolic syndrome and related disorders found lower fasting glucose and insulin (Hamedifard et al.).; Chlorella: A 2026 review of 24 studies found lower insulin resistance and insulin, but rated the certainty of evidence very low for most outcomes, low for body mass index (Mardani et al., Nutrition & Diabetes).
• Outcome: Allergic rhinitis; Spirulina: One double-blind, placebo-controlled trial reported better nasal symptoms with spirulina (Cingi et al., 2008). It is one trial.; Chlorella: Not studied in the sources we found.

How to read the table. The meta-analyses disagree on some outcomes, partly because they include different trials and populations. Many pooled trials are small, short and heterogeneous, and the authors themselves ask for better trials. The most recent chlorella review, with 24 studies, concluded that, given the overall very low certainty of evidence, results should be interpreted cautiously. The 2025 comparison of both microalgae calls the spirulina blood-pressure effect small. Our reading: the signal is worth studying, and the best-supported outcomes are blood markers rather than anything you'd notice day to day.

No study we found compared chlorella and spirulina head to head in the same trial; the 2025 review analysed them separately.

Quality and safety: where the two differ

"Natural" isn't a safety assessment, and the questions differ between these two organisms. None of this is a reason to worry about food you already enjoy; it's a list of things worth knowing before you choose.

Contamination. Spirulina is often grown in open ponds, where toxin-producing cyanobacteria can intrude. In an analysis of 18 commercial algae supplements containing spirulina or Aphanizomenon flos-aquae, eight contained cyanotoxins above tolerable daily intake values (Roy-Lachapelle et al., 2017, Toxins). A 2023 study of five retail spirulina products found microcystins in all of them, at levels that could lead to consumers exceeding recommended daily limits (Rhoades et al., 2023, Microorganisms). In contrast, data from 95 French small-scale producers (623 dry samples tested for microcystins, 2013 to 2021) stayed within the safe regulatory level (Pinchart et al., 2023, Toxins). Results differ with sourcing and testing, and none of these samples represents a product you'll buy.

A 2025 analysis (International Journal of Molecular Sciences) of 52 spirulina and chlorella products (29 conventional, 23 organic) found all complied with EU limits for toxic metals, but detected pharmaceutical residues, with caffeine the most frequent, and raised concern about aluminium measured against tolerable weekly intake. It found no significant difference between organic and conventional products within each algal type (Sochacka et al., 2025). A clean report on one set of toxins says nothing about the others, so a batch certificate is worth most when it names what was tested and the limit applied.

Autoimmune conditions. A 2025 literature review found five published cases in which spirulina use was followed by the onset or flare of autoimmune disease: dermatomyositis in three and pemphigus in two, with timing from one or two days to a year. All five stopped spirulina and received steroid treatment (de Carvalho and Martinez, 2025). Case reports can't prove cause, and they say nothing about how often it happens. An in-vitro study found spirulina stimulated inflammatory signalling in cells from dermatomyositis patients (Bax et al., 2023, iScience). If you have an autoimmune condition, ask your specialist before using spirulina.

Phenylketonuria (PKU). People with PKU follow a diet that limits phenylalanine, supervised by a metabolic dietitian (UK Health Security Agency). Both powders are about half protein, so our reasoning is that a protein-rich supplement is a question for that dietitian. We didn't find a study specific to PKU.

Anticoagulants. Chlorella: a 1995 Japanese case report describes a 75-year-old man whose thrombotest values, well controlled on warfarin, rose above the therapeutic limit after he began chlorella; the authors suggested its vitamin K content (Ohkawa et al., 1995, Rinsho Shinkeigaku; the paper is in Japanese, with an English abstract). It's a single case. Chlorella contains vitamin K, so our reasoning is that anyone on warfarin should ask the prescriber before starting it. No source we found covers a spirulina interaction with anticoagulants.

Immunosuppressant medicines. We found no interaction study for either powder, so if you take them, ask your prescriber first.

Iodine and thyroid. Algae can carry iodine, and too much or too little matters for the thyroid. In a 2024 analysis of edible algae, two spirulina samples measured 1.63 and 1.07 mg/kg and two chlorella samples 2.20 and 3.17 mg/kg; the authors noted most commercial algae packaging doesn't state iodine (Foods, 2024). That is four samples, so treat it as an illustration. Products that blend in seaweed, such as wakame, are another matter. With a thyroid condition, check the label and ask your clinician.

Pregnancy and breastfeeding. We didn't find reliable evidence on spirulina or chlorella in pregnancy or breastfeeding, so ask a midwife or GP.

Where they stand in Dutch and EU food law (8 October 2026)

A review of EU microalgae law lists Arthrospira platensis, Spirulina sp. and several Chlorella species (including C. vulgaris, C. pyrenoidosa and C. sorokiniana) among microalgae products with a consumption history in the EU before 15 May 1997, according to the Novel Food Catalogue as accessed in February 2023 (Foods, 2023). We couldn't confirm the current EU novel-food status of the species in any given product, so check the Commission's Novel Food Status Catalogue before buying.

The same review notes reports of hazardous components in cyanobacteria- and chlorella-containing supplements. We didn't find an EU limit for microcystins in food supplements, and we haven't checked further Dutch rules. On labels, EU supplement rules require a recommended daily dose and a warning not to exceed it, and forbid claims to treat or cure a disease (Your Europe). Rules change; check the current position.

What one Dutch supplier lists (as of 8 October 2026)

PLNKTN is a Dutch brand selling spirulina, chlorella and a plankton blend. Here is what its pages said on 8 October 2026. It's supplier information, not our measurement: we haven't tested any of it, and we haven't seen batch reports.

• Product: Spirulina capsules; Listed details: Arthrospira platensis, 4 capsules (2 g) a day, freeze-dried ("vriesdrogen"), grown in closed photobioreactors in the Netherlands; 65% protein; phycocyanin 285 mg per 2 g serving (about 14%); Price on the page: €29.95 for a 30-day supply
• Product: Spirulina nibs; Listed details: Crunchy nibs, "1 ingrediënt, 65% pure eiwitten"; serving size and phycocyanin amount not stated; Price on the page: €29.95 for 150 g
• Product: Chlorella capsules; Listed details: 4 capsules a day (2 g), 23 mg chlorophyll, 1.7 µg vitamin B12; grown in closed fermentation tanks in Oldenzaal; "gecontroleerd per batch op zuiverheid" (batch-checked for purity, as the supplier states).; Price on the page: €29.95 one-off
• Product: Plankton capsules; Listed details: Blend of Chlorella sorokiniana, Limnospira platensis, Lithothamnium calcareum and Undaria pinnatifida (a seaweed, so worth an iodine check with a thyroid condition); 2 g (4 capsules) a day; Price on the page: €36.95 for 120 capsules

A per-gram sum, using the spirulina row: 4 capsules a day for 30 days is 120 capsules, so €29.95 buys about 60 g of spirulina, roughly €0.50 per gram on the one-off price. Compare any product per gram of the thing you're after, not per bottle.

On pregnancy and breastfeeding, PLNKTN's spirulina page says it recommends talking to a doctor first, because there is too little research on algae in those periods.

If you do pick one

Decide what you're after first: nutrients, protein, a particular blood marker, or curiosity. The evidence differs for each, as the outcome table shows. Then compare products per serving and per gram, look for the species named in full, and prefer a batch report that says which tests were run and which limits were applied. If an earlier caution applies to you (autoimmune conditions, PKU, thyroid disease, anticoagulants, immunosuppressants, pregnancy or breastfeeding), check with a clinician or pharmacist first. Taking both at once is a choice rather than a strategy: no trial we found tests the combination. Our interactions guide and label guide help with the checking.

Where to read next

More from the algae and gut shelf:

• Omega-3: EPA, DHA, fish and algae, for how to read EPA and DHA and how fish, krill and algae oils differ.
• Astaxanthin: what the research shows and what it does not, for the red algae pigment, outcome by outcome, with doses, funding and EU limits.
• Probiotics, prebiotics and postbiotics, for what each term means and how to read a pack.

Written by Smart Supplements with AI assistance from the sources linked in the text. It has not been reviewed by a clinician.

Last updated: 12 October 2026

This article is for informational purposes only and is not intended as medical advice. Always consult a healthcare professional before starting any new supplement, especially if you take prescription medication.