Spirulina: Protein, Iron and the Blue Pigment Phycocyanin

Spirulina (Arthrospira platensis) isn't just another green powder. It is a blue-green microalga that is dried and eaten as a food. Here's the full story.

Spirulina is a cyanobacterium — a microscopic, spiral-shaped, blue-green photosynthetic organism that has thrived in alkaline lakes for billions of years. It's not technically a plant or a true alga (it's prokaryotic), but for nutritional purposes it behaves like one: it grows in water using sunlight and CO₂, fixes nitrogen, and accumulates remarkably high concentrations of protein, vitamins, minerals, and pigments.

The two species commercially cultivated for human consumption are Arthrospira platensis and A. maxima. Spirulina is grown commercially in controlled ponds.

Per 100 g of dried Spirulina powder you'll typically find:

• Protein: 60-70 g — and it's a complete protein (all 9 essential amino acids).

The protein percentage by weight is what most often draws attention. By dry weight spirulina contains more protein than pulses; one 500 mg capsule provides about 0.3 g of protein. The catch: a typical daily Spirulina dose is 1-3 g, not 100 g — so the absolute protein contribution to a meal is small. The value is in micronutrient density, not macro-protein delivery.

This is where Spirulina gets controversial. Spirulina contains compounds that register on common B12 blood tests, but a significant fraction is pseudocobalamin — a B12 analogue that the human body can't fully convert to active forms (methylcobalamin and adenosylcobalamin). Studies in the 1990s (Watanabe et al.) suggested 80%+ of Spirulina's B12 content was pseudocobalamin. More recent work (van den Berg et al., Nutrition Reviews) is more nuanced and notes that some Spirulina cultivars carry meaningful active B12.

Practical guidance: do not rely on Spirulina alone if you're vegan and have no other B12 source. Use a dedicated methylcobalamin or cyanocobalamin supplement (or B12-fortified foods) for guaranteed coverage, and treat Spirulina's contribution as a bonus, not a substitute.

Phycocyanin is the molecule that gives Spirulina its blue-green colour. Phycocyanin is the pigment that gives spirulina its blue-green colour.

Phycocyanin is not on the UK Nutrition and Health Claims Register of authorised health claims, so we don't make any specific health claim for it on our label or in our copy. Spirulina extract is also used in the food industry as a blue colouring.

Our Spirulina capsules contain 500 mg of pure Spirulina (Arthrospira platensis) powder per capsule, in a plant-based HPMC capsule shell. The full ingredient list is just two items: Spirulina powder and the capsule shell. No flow agents, no titanium dioxide, no proprietary blend.

One thing worth noting on the label: "Contains naturally occurring sulphites". Spirulina contains trace amounts of sulphites as a natural metabolic by-product. This is required allergen disclosure under UK Reg 1169/2011 — it's not added sulphites, just trace levels naturally present in the algae. People with a known sulphite sensitivity should be aware.

Dose: take 1 capsule daily with water, preferably with food, as on the label. Do not exceed the stated dose.

Timing: with breakfast or lunch is ideal. Coffee and tea inhibit iron absorption, so if iron uptake matters to you (e.g. if you're vegetarian or low on ferritin), space your Spirulina away from caffeinated drinks by at least an hour.

• Phenylketonuria (PKU): Spirulina is high in phenylalanine and not suitable.
• Autoimmune conditions: in theory Spirulina's immunomodulating compounds could activate immune pathways; if you have lupus, MS, RA, or similar, check with your specialist before starting.
• Anticoagulant therapy: Spirulina's vitamin K content is modest but worth flagging if you take warfarin.
• Sulphite sensitivity: see allergen note above.
• Pregnancy: limited high-quality data — speak to your midwife before starting.

Spirulina cultivated in poorly-managed open ponds can accumulate heavy metals (cadmium, lead, mercury) or microcystin contamination from co-occurring blue-green algae species.

Spirulina + Moringa is the classic "green pair" — Moringa brings the broader vitamin-mineral spectrum (high vitamin A, calcium, iron, potassium), Spirulina brings the protein density and phycocyanin. Some customers take spirulina and moringa together.

Vitamin C increases iron absorption. MSM is an organic sulphur compound.

Can I take Spirulina every day?

Yes — 1 capsule daily, as on the label. Most users take it daily with breakfast. No cycling required.

Will Spirulina turn things green?

The capsule itself is opaque and won't stain your hands. If you opened the capsule, the powder is intensely blue-green and will stain countertops, fabric, and tongues. Just take it as a capsule with water and you'll be fine.

Is your Spirulina vegan?

Yes. Capsule shell is HPMC (plant-derived); ingredient is just Spirulina (Arthrospira platensis) powder.

Will it interfere with my morning coffee?

It won't interfere with the coffee, but caffeine and tannins in coffee/tea reduce iron absorption from any food source — including Spirulina. If iron uptake matters to you, separate them by 60+ minutes.

Does Spirulina actually replace B12?

No — see the B12 question above. Use a dedicated methylcobalamin / cyanocobalamin supplement for reliable B12 status, and treat Spirulina's B12 contribution as a bonus.

Our Spirulina is 500 mg of pure Arthrospira platensis per vegan capsule, 120 capsules per pot. It's not a magic bullet, and it doesn't replace a B12 supplement, but as a daily green it earns its space in the daily stack. Browse our 500 mg vegan capsules (120 count) →

Educational only. Not medical advice. Contains naturally occurring sulphites. Not suitable for people with PKU. Pregnant or breastfeeding women, people with autoimmune conditions, or those on anticoagulant therapy should consult a doctor before supplementing Spirulina.