Spirulina

botanical

What is it

Spirulina is a blue-green microalga (cyanobacterium) of the genus Arthrospira, primarily A. platensis and A. maxima. It is one of the oldest life forms on Earth and is cultivated as a nutritional supplement valued for its high protein content and dense nutrient profile.

How it works

Spirulina is exceptionally nutrient-dense by weight. It contains 55 to 70% protein with all essential amino acids (though lower in methionine than animal proteins), substantial amounts of B vitamins, iron, copper, magnesium, and the antioxidant pigment phycocyanin, which gives spirulina its blue color and accounts for many of its proposed biological effects. Phycocyanin has anti-inflammatory and antioxidant activity, inhibiting cyclooxygenase enzymes and scavenging free radicals. Spirulina also contains gamma-linolenic acid (GLA), chlorophyll, carotenoids (beta-carotene, zeaxanthin), and various polysaccharides studied for immune-modulating effects. Spirulina is unusual in that it provides plant-source vitamin B12, but most of this B12 is in 'pseudovitamin' form that is not bioactive in humans, so it should not be considered a reliable B12 source for vegans. As a dense source of iron, it may contribute meaningfully to iron status, particularly in plant-based diets.

Evidence for 6 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Cholesterol and lipid markers

Grade C

Moderate evidence

Meta-analyses suggest spirulina supplementation may modestly reduce total cholesterol, LDL cholesterol, and triglycerides while raising HDL. Effects are small to moderate.

Blood pressure

Grade C

Moderate evidence

Some studies suggest spirulina may modestly reduce blood pressure, especially in people with hypertension. Effects are generally small.

Anemia and iron status

Grade C

Moderate evidence

Spirulina is iron-rich and some studies in iron-deficient populations suggest it may improve hemoglobin levels. It is not a substitute for iron supplements in clinically significant iron deficiency.

Allergic rhinitis

Grade C

Moderate evidence

A few clinical trials suggest spirulina may reduce nasal symptoms in allergic rhinitis. Evidence is limited but consistent.

Exercise performance

Grade C

Moderate evidence

Some small studies suggest spirulina may improve endurance, reduce exercise-induced oxidative stress, or extend time to exhaustion. Effects are typically small.

Glucose control

Grade C

Moderate evidence

Some research in type 2 diabetes suggests modest improvements in fasting glucose and HbA1c with spirulina supplementation. Not a substitute for diabetes management.

4 commercial forms

Spirulina powder

Standard form; can be mixed into smoothies or foods.

Cost-effective per gram. Distinct earthy/marine taste.

Spirulina tablets/capsules

Convenient dosing; same composition as powder.

Multiple tablets often needed for therapeutic doses. Easier to take than powder.

Organic/USDA-certified spirulina

Subject to organic standards; reduced contamination risk.

Higher cost but better quality assurance.

Phycocyanin extract

Concentrated form of the active blue pigment from spirulina.

Specialty product; may have different effects than whole spirulina.

Dosage

Typical doses range from 1 to 10 g per day. Clinical studies have used 1 to 8 g per day for various indications, with 3 to 4 g being a common dose. It can be taken as tablets, capsules, or powder mixed into smoothies. There is no established Tolerable Upper Intake Level.

When and how to take it

WHEN: Take spirulina at any time of day. Many users take it with breakfast or in a smoothie. HOW: Take with water or mix into smoothies, juice, or yogurt. Quality matters substantially due to contamination risks; choose third-party tested products. Start with a small dose to assess tolerance.

Food sources

Food	Amount	%DV
Spirulina powder (raw)	1 tbsp (~7g)	—
Spirulina-containing smoothie blends	Varies	—

Safety

High-quality spirulina is generally well tolerated. Side effects include mild GI symptoms, headache, and (rare) allergic reactions. There is no established Tolerable Upper Intake Level. The major safety concern is contamination: spirulina grown in poor conditions can contain heavy metals (lead, mercury) or microcystin toxins from contaminating cyanobacteria. Buy from reputable sources with third-party testing. People with phenylketonuria (PKU) should avoid spirulina due to its phenylalanine content.

Who should be cautious

People with phenylketonuria (PKU) should avoid spirulina due to high phenylalanine content. Those with autoimmune disorders should consult a clinician given possible immune-stimulating effects. People on warfarin should monitor INR. Pregnant and breastfeeding women should choose tested, reputable products and consult a clinician. Anyone with seafood or algae allergies should be cautious.

Interactions

Spirulina may have immune-stimulating effects and could theoretically interact with immunosuppressants used in autoimmune diseases or after transplant. Its vitamin K content (though modest) may affect warfarin. It may also modestly affect blood glucose, potentially adding to diabetes medication effects.

Frequently asked questions

Is spirulina a complete protein?⌄

Spirulina contains all essential amino acids but is lower in methionine and cysteine. It contributes meaningful protein but is not the best protein source on a per-gram basis. Adequate methionine should be ensured through other dietary sources.

Is the B12 in spirulina reliable?⌄

No. Most of the vitamin B12 in spirulina is pseudovitamin B12 that is not biologically active in humans. Vegans should not rely on spirulina for B12; use a verified B12 supplement instead.

Is spirulina safe to take daily?⌄

High-quality, third-party tested spirulina is generally safe for daily use. Contamination is the main concern; avoid products from unregulated sources. People with PKU or autoimmune disorders should consult a clinician.

What dose should I take?⌄

Typical doses are 1 to 10 g per day. Clinical studies have used 1 to 8 g per day. Start with a small amount and increase as tolerated.

Does spirulina help with weight loss?⌄

Spirulina is nutrient-dense and modestly satiating, but it is not a weight loss agent. Any contribution to weight loss is secondary to overall diet and activity changes.

References

Wikidata: Spirulina — Wikidata link

Track Spirulina with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

Coming to App Store

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.