Spirulina: what it is, what it provides and what the evidence says

What is spirulina?

Spirulina is the commercial name for cyanobacteria of the genus Arthrospira. They grow in warm, alkaline fresh water and are dried to be sold as a powder, tablets or an ingredient in other foods [2]. It is not a seaweed, so claims about seaweed and iodine do not apply; we discuss those in the iodised salt guide.

The older name “Spirulina” is also used on labels and in studies. When comparing products, check the species listed, the manufacturer and the controls. Composition varies by cultivation conditions and batch [2], so figures in a database are an approximate reference [1].

What does a typical amount provide?

The FoodData Central entry lists 57.47 g of protein and 28.5 mg of iron per 100 g of dried spirulina [1]. Those 100 g are useful for comparing foods, but nobody takes that amount.

In the amounts usually found in a supplement, spirulina provides little protein and iron compared with foods such as pulses, eggs or yoghurt [1] [2]. It does not replace a varied diet or treatment prescribed by a professional.

The iron in spirulina is not necessarily absorbed in the same way as iron from other foods. In a vegetarian eating pattern, the overall mix of iron sources and what accompanies the meal matter [4]. If a blood test shows a deficiency, the amount on the label does not replace an assessment of its cause.

Is it a source of vitamin B12 in a vegan diet?

Do not rely on spirulina to provide B12. Most of what is measured as B12 in spirulina is a similar form that the body cannot use [2]. That is why the “B12” figure on a label can give a false sense of security.

If you follow a vegan diet, read how to plan a vegetarian or vegan diet and agree on a reliable source of B12 with your dietitian-nutritionist. If you eat eggs or dairy, this is discussed in common mistakes in vegetarian diets.

What does the evidence say about cholesterol, blood glucose and weight?

A review of 28 trials in adults with excess weight found small average reductions in weight, total cholesterol, LDL cholesterol and triglycerides with spirulina [3]. It found no changes in blood glucose or fasting insulin, and the certainty of several results was very low [3].

This is a preliminary signal: the trials included different populations, products and durations, and none shows that spirulina prevents heart attacks or controls diabetes [3]. If you already have a medical plan, keep following it and discuss any supplement with the professional treating you.

The European register of nutrition and health claims contains no authorised claim for spirulina relating to cholesterol, blood glucose or weight [5], so its label cannot promise these effects.

To address your figures, the diet guide for high cholesterol explains the dietary approach and its medical limits. The response to a blood test depends on overall risk and treatment, not on one isolated ingredient. On berberine, another supplement studied for blood glucose and cholesterol, there is a guide summarising what the evidence says.

Product safety and quality

ANSES’s safety assessment warns of possible contamination with microcystins, other cyanobacteria or metals such as lead, mercury and arsenic [2]. Most products analysed that contain only spirulina do not show concerning levels, but the source, cultivation and batch controls matter [2].

If you have phenylketonuria, do not take it on your own: it contains phenylalanine, and any change should be decided with the team managing your diet [2]. ANSES also warns about a history of allergies. A previous reaction to a supplement should be assessed before you use it again [2].

If you have an autoimmune disease, get advice before taking it [6]. Reports describe coinciding flare-ups, but these cases do not prove that spirulina caused them.

If you take regular medication, ask your pharmacist or doctor whether spirulina interacts with it [7]. Possible interactions with certain medicines have been raised, but their clinical importance remains unclear. Do not change or stop medication to try a supplement.

The word “natural” does not guarantee safety. In the medicinal plants guide, we explain how to assess other products that promise health benefits. In either case, ask what specific benefit you expect and what risk the product adds.

What we see in consultations

The question that comes up most often is whether an average improvement in a trial means it will work for you. You cannot know without measuring: before buying anything, we agree on which figure you want to change and when to check it again.

Another frequent question is whether spirulina can make up for an improvised vegan diet. B12 requires a reliable source [2]. For other nutrients, we review what you eat, what you need and what your blood test shows before adding anything.

Is it worth buying?

If you like its taste or colour, you can consider using it as an occasional ingredient and check where it comes from. Price, convenience and quality matter too. You do not need to include it to have a complete diet.

If you buy it to improve cholesterol, blood glucose or weight, what affects those figures is your overall eating pattern, not one ingredient.