Spirulina, also known as cyanobacteria or blue-green algae, was reportedly used as food during the Aztec civilisation in the 16th century. Over the past few decades, millions of people worldwide have adopted spirulina as a food supplement. NASA and the European Space Agency have even designated it as essential nutrition for astronaut missions, which speaks to its nutrient density if nothing else.

But here’s the thing: just because astronauts eat something doesn’t automatically make it a cure-all. Let’s look at what the research actually shows about spirulina’s benefits and where the evidence falls short.

What is spirulina?

Spirulina refers to a class of photosynthetic filamentous single-celled organisms in the phylum Cyanobacteria. The name comes from the spiral form of its filaments. The most commonly studied species are Arthrospira maxima, Spirulina platensis, and Spirulina fusiformis.

In terms of nutritional content, spirulina is genuinely impressive. It contains roughly 60-70% protein by dry weight, which is higher than most meat and fish. This makes it particularly useful for vegetarians looking to boost protein intake. Beyond protein, spirulina contains:

Beta-carotene and phycocyanin (the blue pigment that gives spirulina its colour)
Trace minerals: potassium, sodium, calcium, magnesium, iron, zinc
Vitamins: vitamin B12 and vitamin E
Fatty acids: gamma-linolenic acid (GLA) and phenolic compounds
Phytochemicals: chlorophyll, astaxanthin, lutein

One practical advantage of spirulina is that its cell wall is extremely thin, making it highly water-soluble with an absorption rate reportedly around 95%. This is better than many other algae-based supplements.

Spirulina has been proposed to have anti-cancer, immune-stimulating, anti-inflammatory, and antidiabetic properties. However, proposed benefits and proven benefits are different things, so let’s examine what controlled trials have actually found.

What are the evidence-based benefits of spirulina?

1. Nutritional density makes it a reasonable multivitamin alternative

I should be clear upfront: spirulina isn’t going to replace a balanced diet. But as supplements go, its nutrient profile is genuinely impressive. The combination of complete protein, essential fatty acids, minerals, and antioxidant compounds in a single food is relatively unusual.

For people who struggle to eat varied diets, whether due to dietary restrictions, food access issues, or simply poor eating habits, spirulina provides a concentrated source of multiple nutrients simultaneously. The phytochemicals (phycocyanin, chlorophyll, beta-carotene) have antioxidant properties that have been demonstrated in laboratory settings, though translating test-tube results to meaningful human health effects is always tricky.

2. Spirulina may assist weight loss (modest effects)

A 2019 systematic review and meta-analysis examined 5 randomised controlled trials with 278 participants [1]. The analysis found that spirulina supplementation helped reduce body weight, body fat percentage, and waist circumference. However, there were no significant changes in body mass index or waist-hip ratio.

Subgroup analysis showed that obese participants had larger weight changes than those who were merely overweight. The proposed mechanisms include reducing fat accumulation in the liver, improving oxidative stress markers, and potentially affecting appetite regulation.

My honest take: The effects exist but are modest. If you’re expecting dramatic weight loss from spirulina alone, you’ll be disappointed. It might provide a small additional benefit on top of diet and exercise, but it’s not going to do the heavy lifting for you.

3. Limited evidence for type 2 diabetes improvement

A 12-week randomised controlled trial with 37 patients with type 2 diabetes found that 8 grams of spirulina daily reduced malondialdehyde (an oxidative stress marker) and triglycerides while increasing adiponectin levels [2].

However, here’s what didn’t change: fasting blood glucose, glycated haemoglobin (HbA1c), insulin, total cholesterol, LDL cholesterol, and HDL cholesterol. The things that most diabetics care about monitoring showed no significant improvement.

Bottom line: The evidence for spirulina improving diabetes control is weak. The one positive trial shows effects on secondary markers but not the primary outcomes that actually matter for disease management.

4. Possible benefits for male infertility (preliminary evidence)

Male factors contribute to roughly half of all infertility cases, and about 60-75% of male infertility cases are classified as idiopathic because the underlying mechanisms remain unknown.

A placebo-controlled trial over 12 weeks with 40 men with idiopathic infertility compared 2 grams of spirulina daily against placebo [3]. The results were mixed: there was no significant difference in semen parameters (count, motility, morphology) between groups. However, the pregnancy rate was 5% in the spirulina group versus 0% in the control group.

I should be honest here: a 5% pregnancy rate from 40 participants isn’t statistically robust. This is a single small trial, and drawing strong conclusions would be premature. More research is needed before recommending spirulina specifically for fertility.

5. Spirulina appears helpful for allergic rhinitis

Allergic rhinitis affects about 20-30% of adults and up to 40% of children, causing symptoms like nasal congestion, runny nose, sneezing, and itchy nose. The condition often leads to poor sleep, fatigue, and reduced quality of life.

A 6-month randomised, double-blind, placebo-controlled study with 150 patients with allergic rhinitis found that spirulina significantly improved all measured symptoms: runny nose, sneezing, nasal congestion, and itching [4].

This is probably the strongest evidence for any spirulina benefit. The trial was reasonably sized, properly controlled, and ran for a meaningful duration. If you’re considering spirulina for a specific purpose, allergic rhinitis has the best supporting evidence.

6. May reduce fatigue (very limited data)

An 8-week randomised, double-blind, placebo-controlled study with 18 healthy men found that oral spirulina improved both mental and physical fatigue scores [5].

The obvious limitation: 18 participants is tiny. This is hypothesis-generating research, not definitive proof. I wouldn’t recommend spirulina specifically for fatigue based on this single small trial alone.

7. Potential benefits for chronic hepatitis C

Around 50-80% of people with acute hepatitis C infection develop chronic infection, and these patients face significant risks of cirrhosis (20%) and hepatocellular carcinoma (4-5% per year).

A 6-month randomised study comparing spirulina to silymarin (milk thistle) in 66 patients with chronic hepatitis C found that spirulina improved viral load, liver function markers, and quality of life scores compared to the silymarin group [6].

This is interesting but needs context: the comparison was against another supplement, not against standard medical treatment or placebo. Also, hepatitis C now has highly effective antiviral treatments available, so spirulina would at best be a complementary approach, not a primary treatment.

8. May help thalassaemia patients reduce transfusion frequency

Beta-thalassaemia major is an inherited blood disorder requiring regular blood transfusions, which can lead to iron overload complications affecting the heart, liver, and endocrine system.

A 3-month study with 60 children with thalassaemia major found that spirulina improved haemoglobin levels and cardiac function markers while reducing the number of blood transfusions needed [7].

Important caveat: This was an interventional study, not a randomised controlled trial. The results are promising enough to warrant further research, but thalassaemia patients should not adjust their transfusion schedules based on this single study alone.

9. Possible benefits for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease is now the most common chronic liver disease, with prevalence of 50-75% in people with type 2 diabetes and 80-90% in obese patients.

A 6-month study with 14 patients found that spirulina reduced liver enzymes (AST, ALT, GGT), LDL cholesterol, total cholesterol, and insulin resistance markers [8]. HDL cholesterol and quality of life scores improved.

The problem: 14 participants is far too small to draw reliable conclusions. The effect sizes were meaningful, but this needs replication in larger trials before recommending spirulina specifically for fatty liver.

10. May improve nutritional status in malnourished children

A 30-day study with 50 malnourished African children found that spirulina significantly improved haemoglobin levels, reduced anaemia, and increased total protein [9].

In resource-limited settings where diverse food access is challenging, spirulina’s nutrient density could be genuinely valuable. This is perhaps the most practical application: a concentrated, shelf-stable source of protein and micronutrients for populations at risk of malnutrition.

11. Potential detoxification properties (mainly animal data)

A systematic review found that spirulina can help organisms counteract certain toxic substances including arsenic, carbon tetrachloride, and hexachlorocyclohexane (HCH) [10].

Major limitation: Most of this research comes from animal experiments. While the mechanisms are biologically plausible, extrapolating animal toxicology data to human health recommendations is always questionable. We don’t have good human trials on spirulina for detoxification purposes.

12. Spirulina may improve blood lipid profiles

A systematic review and meta-analysis of 7 studies with 552 participants found that spirulina lowered total cholesterol, LDL cholesterol, and triglycerides while raising HDL cholesterol [11].

The proposed mechanism involves phycocyanin slowing cholesterol absorption, scavenging free radicals, and reducing pro-inflammatory cytokines.

My assessment: The effect sizes are modest but consistent across studies. If you’re looking for natural approaches to support healthy cholesterol alongside diet and exercise, spirulina is one reasonable option, though it won’t replace statins for people who need significant cholesterol reduction.

Are there side effects from spirulina?

If spirulina is grown in unpolluted conditions, it’s generally considered a very safe food. Humans have consumed it for thousands of years, reportedly dating back to ancient Egypt.

Reported adverse effects are usually mild and include:

Nausea and vomiting
Diarrhoea and abdominal discomfort
Fatigue and headache
Dizziness
Oedema
Muscle pain
Facial flushing and sweating

The more serious concern is contamination. Spirulina absorbs whatever is in its growing environment, so products from polluted water sources may contain bacteria, toxic metals, or microcystin (a dangerous algal toxin). Contaminated products have been associated with liver damage, rapid heartbeat, and in severe cases, shock.

Practical advice: Only purchase spirulina from reputable brands that provide third-party testing certificates. The supplement industry has quality control issues, and algae products are particularly vulnerable to contamination problems.

Safety precautions: 7 contraindications to note

Pregnancy and breastfeeding: Safety is unknown, so avoidance is recommended
Iodine allergy or hyperthyroidism: Spirulina contains iodine which could worsen these conditions
Seafood or seaweed allergies: Cross-reactivity is possible
Autoimmune diseases: Spirulina activates immune cells, which could aggravate conditions like multiple sclerosis, systemic lupus erythematosus, or rheumatoid arthritis
Phenylketonuria (PKU): Spirulina contains phenylalanine, which people with PKU cannot metabolise properly
Bleeding disorders or anticoagulant medications: Spirulina has anticoagulant effects that could increase bruising and bleeding risk
Immunosuppressant medications: Spirulina’s immune-stimulating effects may interfere with drugs like azathioprine, cyclosporine, tacrolimus, sirolimus, prednisone, and other corticosteroids

References

Moradi S, et al. The effects of spirulina (Arthrospira platensis) supplementation on anthropometric indices: A systematic review and meta-analysis of controlled clinical trials. Phytother Res. 2019;33(11):2776-2788. PubMed
Parikh P, et al. Role of Spirulina in the Control of Glycemia and Lipidemia in Type 2 Diabetes Mellitus. J Med Food. 2001;4(4):193-199. PMC
Khorami MH, et al. The effects of spirulina platensis on the reproductive function of male idiopathic infertile patients: A single-blinded controlled study. Int J Reprod Biomed. 2018;16(5):327-332. PubMed
Cingi C, et al. The effects of spirulina on allergic rhinitis. Eur Arch Otorhinolaryngol. 2008;265(10):1219-1223. PubMed
Johnson M, et al. A randomized, double-blind, placebo-controlled study of spirulina supplementation on indices of mental and physical fatigue in men. Int J Food Sci Nutr. 2016;67(2):203-206. PubMed
Yakoot M, Salem A. Spirulina platensis versus silymarin in the treatment of chronic hepatitis C virus infection. A pilot randomized, comparative clinical trial. BMC Gastroenterol. 2012;12:32. PMC
Hamdy M, et al. Spirulina may improve spleen function in patients with beta thalassemia major by its antioxidant and anti-inflammatory effects. Pediatr Blood Cancer. 2019;66(4):e27500. PubMed
Mazokopakis EE, et al. Beneficial effect of spirulina supplementation on improving parameters of NAFLD: A pilot study. Phytother Res. 2014;28(10):1550-1556. PMC
Simpore J, et al. Nutrition rehabilitation of undernourished children utilizing Spiruline and Misola. Nutr J. 2006;5:3. PubMed
Abdel-Daim MM, et al. Spirulina platensis protects against furan renal toxicity via its antioxidant and antiapoptotic mechanisms. Environ Sci Pollut Res. 2015;22(21):16943-16950. PubMed
Serban MC, 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. PubMed
NHS. Vitamins and minerals. NHS Website
NIH National Center for Complementary and Integrative Health. Blue-Green Algae. NCCIH Website