Spirulina: dangers for the liver, quality, and dosage

Spirulina has been consumed for centuries and industrially cultivated since the 1970s. For a healthy person, a product from a controlled supply chain poses no particular problem. But there is a real issue, and it needs to be clearly stated: the risk does not come from spirulina itself; it comes from how it was produced. This is what makes all the difference between two jars at the same price.

What exactly is spirulina?

First surprise: it's not an algae, even though it's commonly called that. It's a cyanobacterium, a filamentous microorganism in the shape of a spiral—hence its name—that grows in warm, alkaline waters. The cultivated genus is called Arthrospira.

Its composition explains its popularity:

A large proportion of proteins, more than half of its dry weight. This is a lot, but let's put it into perspective: no one eats 100g of spirulina. At 3g per day, we're talking about approximately 2g of protein—the equivalent of half a scoop of protein powder. Spirulina is not a protein source; it's a micronutrient concentrate.

Phycocyanin, the blue pigment that gives it its distinctive color, often highlighted as a quality marker.

Beta-carotene, iron, and B-group vitamins.

From a regulatory standpoint, the rule is the same as for all plants and microorganisms: no health claims are permitted in Europe for spirulina. We describe what it contains, not what it would do.

The real issue: production quality

This is the core of this page and the most useful information we can give you.

Spirulina is an organism that concentrates what is in its culture medium. Cultivated in clean water, with controlled inputs, it is clean. Cultivated in questionable water, it concentrates whatever is in it: heavy metals, or toxins produced by other cyanobacteria that develop in the same pond.

French health authorities have examined the issue, and their conclusion is precisely this: the risk is linked to production control, not to spirulina. This also explains the cases of contaminated products that periodically appear in the press, concerning batches purchased without any traceability.

What this means for you, concretely: origin and controls matter more than the price per kilo. Spirulina from an identified, certified, and analyzed supply chain is worth its price difference. This is the number one criterion we apply before listing a product, and it is for this reason that we only offer one reference: Nutriting's organic, high-concentration nuSpiruline, on the spirulina page.

Spirulina and the liver: what should you think?

This question comes up a lot, and the answer follows directly from the above.

Clean spirulina is not known to cause liver problems in healthy individuals. Cases of liver damage reported with this type of product are associated with contamination by cyanobacterial toxins, some of which specifically target the liver. In other words: the problem is not spirulina; it's what grew alongside it in a poorly controlled pond.

The practical conclusion is simple and reassuring: choose a controlled supply chain, and this question no longer arises. And as always, unusual fatigue, dark urine, or yellowing of the skin requires discontinuation and consultation, regardless of the product concerned.

Who should abstain or seek advice?

The list is short but precise.

Heavy smokers. This is a little-known point and deserves to be mentioned: spirulina is rich in beta-carotene, and large trials conducted with high doses of beta-carotene in smokers observed an increased risk of lung cancer. As a precaution, heavy smokers should discuss this with their doctor before a prolonged course.

People with phenylketonuria, as spirulina contains phenylalanine.

People on anticoagulants, due to the presence of vitamin K: this is a question to ask the treating doctor.

People with an autoimmune disease or on immunosuppressive treatment, as a matter of caution.

Additionally, pregnancy, breastfeeding, and minors are included due to insufficient data.

The question of vitamin B12

This is the point on which we will not follow the usual discourse, because it is important.

Spirulina often boasts an impressive vitamin B12 content. The problem is that much of this B12 consists of analogues inactive in humans: similar molecules that assays count, but which the body cannot use.

In concrete terms: spirulina should not be considered a reliable source of B12, especially in a vegan diet where this vitamin is a critical point. We explain this in detail in our article on vitamin B12, and the B vitamins section offers forms that are active.

We prefer to sell you a B12 for a few euros that works, rather than letting you believe that a spoon of spirulina is enough.

What dosage, and how to start?

1 to 5g per day, with a gradual increase: start with 1g for a week, then increase. This is the best way to avoid the discomforts of the first few days.

These discomforts are benign and transient: slight nausea, bloating, sometimes a headache. And a peculiarity that often surprises: greenish stools, a simple effect of the pigments, with no significance whatsoever.

Preferably take it with a meal. The marine taste is pronounced in powder form; tablets solve the problem for those who dislike it.

Frequently Asked Questions

What are the dangers of spirulina?

Spirulina from a controlled supply chain poses no particular problem for healthy adults. The real risk comes from poorly controlled products, which may contain heavy metals or cyanobacterial toxins. Origin and controls are the determining criteria.

Is spirulina dangerous for the liver?

Not in itself. Reported cases are associated with contamination by cyanobacterial toxins, which target the liver. A traceable supply chain solves the issue.

How much spirulina per day?

1 to 5g per day, starting with 1g the first week then gradually increasing, preferably with a meal.

Who cannot take spirulina?

People with phenylketonuria, those on anticoagulants or immunosuppressive treatment without medical advice, heavy smokers without medical advice, as well as pregnant or breastfeeding women, and minors.

Why is spirulina not recommended for smokers?

Because it is rich in beta-carotene, and large trials conducted with high doses of beta-carotene in smokers observed an increased risk of lung cancer. Caution is therefore advised, with medical advice.

Does spirulina cause bloating?

Sometimes at the beginning of a course, with mild bloating. A gradual increase in dosage usually resolves the problem.

Why do stools turn green?

This is the effect of spirulina pigments, with no significance or severity.

Is spirulina a good source of vitamin B12?

No. The B12 it contains consists largely of analogues inactive in humans. It should not be considered a reliable source, especially in a vegan diet.

Does spirulina help with weight loss?

No, and no such claim is permitted. Weight loss relies on caloric deficit.

Spirulina and hypertension: is there a risk?

No blood pressure elevation effect has been established. If you are currently on medication, consulting your doctor remains the correct approach.

Spirulina near Montpellier?

Our store is in Vendargues, about ten minutes from Montpellier. Regarding spirulina, our selection process primarily involves elimination: we only list products from an identified and certified supply chain, because that is the only criterion that truly matters here. We also ship everywhere in France and Europe.

Sources: ANSES for work related to spirulina-based food supplements and contamination control, EFSA for the status of claims. This information does not replace medical advice. If you are currently on medication, pregnant, breastfeeding, a heavy smoker, or have a known medical condition, seek your doctor's advice before any supplementation.