Spirulina: the microcystin problem nobody mentions

Spirulina has a genuinely good nutritional case. It is roughly 60% protein by weight, which is unusual for anything from a plant or plant-like source, and that makes it substantive for vegetarian and vegan customers rather than merely fashionable.

It is also the single most contamination-sensitive ingredient we handle, and the reason is a class of compounds almost no spirulina marketing mentions. This article is about that.

What spirulina is

Arthrospira platensis is a cyanobacterium, a blue-green alga, in common usage, cultivated in open ponds or controlled raceway systems, harvested, and spray-dried into powder or compressed into tablets.

It is a cultivated crop, not a wild-gathered herb, and that distinction is the whole safety story: cultivation can be controlled, and water bodies cannot.

The problem: microcystins

Cyanobacteria as a group include species that produce microcystins, a family of toxins that are specifically hepatotoxic, meaning they damage the liver.

Arthrospira itself does not produce microcystins. The risk comes from contamination: if a cultivation pond is colonised by microcystin-producing cyanobacteria such as Microcystis, the harvested biomass contains both. Open ponds without rigorous monitoring are exactly where this happens, and wild-harvested algae from natural lakes are the highest-risk material of all.

This is not a theoretical concern raised to sell premium product. Microcystin contamination of commercial spirulina supplements has been documented in published surveys of retail products across multiple markets, with a proportion of samples exceeding recommended limits.

Why this is not widely discussed

Three reasons, and the last is the uncomfortable one.

It is invisible. Contaminated spirulina looks, smells and tastes like clean spirulina. There is no consumer-level check.

The harm is slow. Microcystin exposure at low levels does not produce an acute event you would connect to a supplement. It is a liver-burden question over time, not a same-day reaction.

Mentioning it is commercially awkward. A brand that explains the risk is raising a doubt about its own category. Most would rather talk about chlorophyll.

We think that calculation is wrong, and specifically wrong for a brand trying to be trusted. The customers buying spirulina are nutrition-literate and read labels. Being the brand that explained the problem and published its test results is a better position than being one of the many that said nothing.

What actually controls the risk

Three things, in order.

1. Controlled cultivation. Closed or carefully managed raceway systems with monitored water chemistry, rather than open ponds subject to whatever colonises them. This is the primary control and it is a cost difference, not a procedural one.

2. Batch testing for microcystins. Specific analysis for microcystin content on each lot. Not a general heavy-metal panel, a dedicated microcystin assay. This is the check that catches what cultivation controls miss.

3. Documented traceability. Knowing which pond, which harvest, which batch, so that a problem can be isolated rather than guessed at.

In our own handling, spirulina is one of the small number of ingredients we test lot by lot regardless of what the supplier certificate says. The others are shilajit, for heavy metals, and curcumin, for curcuminoid content. In each case the reason is the same: the adulteration or contamination risk is well documented and the consequence of getting it wrong falls on someone who cannot check.

Heavy metals, separately

Spirulina also concentrates minerals from its growth medium, which means lead, arsenic, mercury and cadmium can accumulate if the water or nutrients are contaminated. A standard heavy-metal panel covers this and should be run alongside the microcystin test.

Spirulina grown in industrially polluted water is a real problem in some supply chains. This is another argument for controlled cultivation over the cheapest available source.

What to ask before you buy

If you are a consumer:

• Does the brand state where the spirulina is cultivated?
• Can they provide a batch microcystin test result?
• Do they publish heavy-metal testing?

A brand that cannot answer the second question has not done the test, and the answer “it is 100% natural” is not an answer.

If you are a brand owner:

• Insist on microcystin testing on every lot, in writing, as a specification
• Ask your manufacturer which ingredients they re-test in house and why, if spirulina is not on that list, ask why not
• Require cultivation source documentation
• Budget for it; controlled cultivation costs more and the difference is the product

Who should be cautious regardless

Even with clean material, spirulina is not for everyone:

• Phenylketonuria (PKU). Spirulina contains phenylalanine and should be avoided.
• Autoimmune conditions. Spirulina has immune-modulating effects, so practitioner advice is sensible.
• Immunosuppressant medication. Same reasoning.
• Pregnancy and breastfeeding. Consult a practitioner; the safety data is limited.
• Iodine-sensitive thyroid conditions. Algae products can carry iodine; check with your doctor.
• Gout or high uric acid. Spirulina is high in nucleic acids, which contribute to purine load.

This article is information, not medical advice.

What spirulina may and may not claim

Available: the protein content from a tested batch value in the nutrition panel, the vitamin and mineral content likewise, and general nutritional positioning. Protein and nutrient content claims are nutrition claims and are straightforward.

Not available: claims to detoxify, to treat any condition, to boost immunity in a disease-preventing sense, or to replace medical treatment. Spirulina attracts a great deal of overclaiming internationally and there is no need to add to it, the protein number is a genuinely good story on its own.

The commercial case for doing this properly

Blunt version: the vegan and vegetarian supplement segment in urban India is small, growing quickly, and populated by people who read labels and talk to each other. It is also a segment where a safety story travels fast in both directions.

A spirulina product with published microcystin and heavy-metal testing is differentiated on something real, in a category where almost nobody is differentiated at all. That is worth more than a cheaper cost of goods.

The short version

Spirulina itself does not produce microcystins; contaminating cyanobacteria do, and open-pond or wild-harvested material is where that happens. Contamination is invisible, slow-acting and well documented in retail surveys. The controls are controlled cultivation, per-lot microcystin testing and traceability. Ask for the test result, and if you are a brand, publish it.

For sourcing detail see the spirulina ingredient page. For how we handle lot-level testing, see raw material sourcing and testing and release.