Spirulina is often presented as one of the best sources of plant-based iron. Analysis confirms it: gram for gram, it contains a lot. But how much does a real dose provide, is this iron absorbed, and does it raise ferritin levels?
This guide brings together what product analyses, cell and animal studies, and human trials show. It clarifies what spirulina can provide daily, what it does not replace in case of confirmed deficiency, how to better absorb iron, and the precautions to know.
What spirulina contains : 35 to 146 mg of iron per 100 g in ten supplements analyzed, and up to 666 mg in one batch. But a usual dose is small: 2 g, or 4 tablets, provide 0.7 to 2.9 mg of iron depending on the product, and 10 g provide 3.5 to 14.6 mg. In most products, 78 to 93% of this iron is found in an insoluble form.
What the studies show : in humans, trials are few, short, and contradictory: fewer anemic children with no increase in average hemoglobin or ferritin, serum iron increased in an intestinal disease, hemoglobin increased in one trial with cyclists, not in another. No trial shows an increase in ferritin. Spirulina is therefore a dietary source of iron; a confirmed deficiency requires medical monitoring and an iron supplement, whose effectiveness is measured.
- How much iron does spirulina contain?
- Is this iron absorbed? Data on cells and animals
- What human trials show
- Ferritin and anemia: what spirulina does not replace
- Spirulina or iron supplement?
- Better iron absorption: the rules that matter
- Spirulina and vitamin B12: a false lead
- Quality and precautions
- The plan according to your situation
- Frequently asked questions
How much iron does spirulina contain?
Ten spirulina supplements purchased in Italy were analyzed. Their iron content ranged from 35 to 146 mg per 100 g, a four-fold difference between products. In most of them, 78 to 93% of the iron was found in the insoluble fraction, presumed to be mineral. Cadmium and lead remained below the European limit; aluminum was higher in samples of Chinese origin.
Isani G, Ferlizza E, Bertocchi M, et al. Int J Mol Sci 2022;23(22):13949. DOI: 10.3390/ijms232213949
Other published analyses point in the same direction, with even wider variations: 6 to 107 mg per 100 g in Argentina, 37 to 348 mg in Slovenia. A batch used in a trial in Cambodia even reached 666 mg per 100 g. The iron content of spirulina therefore depends on its origin and cultivation, and only the certificate of analysis of a batch allows you to know it.
| Spirulina Dose | Iron Provided | At average content |
|---|---|---|
| 2 g, or 4 tablets | 0.7 to 2.9 mg | 1.2 mg |
| 5 g | 1.8 to 7.3 mg | 3 mg |
| 10 g | 3.5 to 14.6 mg | 6.1 mg |
| 2 g from the richest batch | 13.3 mg | Exceptional Batch |
As a reference point, iron supplements studied in cases of deficiency provide 25 to 200 mg of iron per dose. Spirulina therefore falls in the category of an iron-rich food, not a treatment. Our ranking of iron-rich foods places it among other sources.
Is this iron absorbed? Data on cells and in animals
No study has measured in humans, by isotopes, the absorption of iron from spirulina. The available data come from intestinal cell cultures and studies in rats.
Iron-enriched spirulina was subjected to simulated digestion, then brought into contact with cultured human intestinal cells. The formation of ferritin, a sign that iron is captured by cells, was 27% higher with beef and spirulina than with yeast and wheat flour; relative to the amount of iron, it was 6.5 times higher with spirulina than with meat.
Puyfoulhoux G, Rouanet JM, Besançon P, et al. J Agric Food Chem 2001;49(3):1625-1629. DOI: 10.1021/jf001193c
However, this result concerns iron-enriched spirulina, which differs from common products. In rats, results diverge: in a 1993 study, anemic rats recovered more hemoglobin with iron sulfate than with spirulina; in a 2019 study, spirulina conversely performed slightly better than iron sulfate, with hemoglobin regeneration efficacy of 54.8% versus 47.2%.
Spirulina iron is bioavailable to the body, as demonstrated by cellular and animal models. But without measurements in humans, we don't know what proportion of a dose is actually absorbed, and the insoluble form that predominates in commercial products warrants caution.
What human trials show
Cambodian children aged 4 to 7 years, living in precarious conditions, received 2 g of spirulina or placebo, 5 days per week for approximately 8 weeks, then reversed. Under spirulina, the number of anemic children decreased by 11, compared to 6 under placebo. However, average hemoglobin, red blood cell volume, and the number of children with low ferritin did not differ, and average ferritin tended to decrease under spirulina. The batch used contained 666 mg of iron per 100 g.
Barennes H, Houdart L, de Courville C, Barennes F. BMC Pediatr 2022;22(1):701. DOI: 10.1186/s12887-022-03766-5
| Study | Participants | Dose and duration | Result on iron |
|---|---|---|---|
| Children, Cambodia, 2022 | 179 children aged 4 to 7 years | 2 g per day, 8 weeks | Fewer anemic children; average hemoglobin and ferritin unchanged |
| Ulcerative colitis, 2023 | 80 adults | 1 g per day, 8 weeks | Serum iron increased versus placebo |
| Cyclists, 2024 | 17 active adults | 6 g per day, 14 days | Hemoglobin +3.4% |
| Cyclists at simulated altitude, 2025 | 20 cyclists | 6 g per day, 3 weeks | Hemoglobin unchanged |
| Obese hypertensive adults, 2016 | 50 adults | 2 g per day, 3 months | Plasma iron decreased versus placebo |
| Seniors, 2011 | 30 adults over 50 years old | 12 weeks | Red blood cell hemoglobin increased, without control group |
The overall assessment is therefore mixed. The trials are small, often conducted in people who did not lack iron, and none focused on women with confirmed iron deficiency or on pregnancy. In the trial of obese adults, plasma iron even decreased under spirulina, possibly because phycocyanin, its blue pigment, binds to minerals—a hypothesis put forward by the authors.
Ferritin and anemia: what spirulina cannot replace
Iron ferritin reflects the body's iron reserves: it is the marker that drops first in case of deficiency, and the one that needs to be raised. Yet no trial shows that spirulina raises it. In Cambodian children, average ferritin tended to decrease with spirulina and increase with placebo; in the ulcerative colitis trial, serum iron increased, but the ferritin result is not reported in the study abstract.
No usable trial compares spirulina to an iron supplement in anemic individuals either: the only trial identified, conducted in India, provides no data in its abstract. Confirmed iron deficiency, low ferritin or anemia, is therefore managed as such: identifying the cause with your doctor, and iron supplementation at an appropriate dose. Our guides low ferritin and iron deficiency detail this approach.
Persistent fatigue, shortness of breath during exertion, paleness, hair loss or heavy periods: these signs warrant a blood test with complete blood count and ferritin, rather than blind supplementation. Iron deficiency always has a cause, which must be identified. See also our guide heavy periods and iron deficiency.
Spirulina or iron supplement?
Iron supplements are based on what spirulina lacks: isotope absorption measurements and randomized trials. Among these, iron bisglycinate, a form where iron is bound to two glycine molecules, was the subject of a meta-analysis.
Seventeen trials of at least 4 weeks compared iron bisglycinate to other forms of iron. In pregnant women, across 9 trials, it resulted in higher hemoglobin, with 64% fewer digestive side effects; ferritin also tended to be higher, without significant difference. In children, no difference was found.
Fischer JAJ, Cherian AM, Bone JN, Karakochuk CD. Nutr Rev 2023;81(8):904-920. DOI: 10.1093/nutrit/nuac106
A Danish trial in 80 pregnant women also showed that 25 mg of iron in bisglycinate form was as effective as 50 mg of iron sulfate for preventing deficiency, with fewer digestive issues. Bisglycinate thus allows for a lower dose, better tolerated. During pregnancy, iron supplementation is always decided with your doctor or midwife. Our comparison iron bisglycinate and other forms details these differences.
| Criterion | Spirulina | Iron supplement |
|---|---|---|
| Iron per dose | 0.7 to 2.9 mg per 2 g | 25 to 200 mg in trials |
| Absorption measured in humans | No | Yes, by isotopes |
| Effect on hemoglobin | Inconsistent across trials | Higher hemoglobin with bisglycinate in pregnant women |
| Role | Dietary iron intake, with proteins and pigments | Correction of deficiency, with medical follow-up |
Better absorb iron: the rules that matter
Iron from plants and supplements, called non-heme iron, is less well absorbed than that from meat: a reference review estimates iron absorption at 14 to 18% with a varied diet, versus 5 to 12% with a vegetarian diet. Several factors modulate it, especially within the same meal.
| Factor | Effect on absorption | In practice |
|---|---|---|
| Vitamin C | Increases it within a meal, more modestly over the entire diet | Pair with a citrus fruit or vitamin C-rich fruit |
| Meat, fish | Increase it | A small portion in the same meal |
| Phytates | Decrease it | Whole grains and legumes away from iron supplements |
| Tea, coffee | Their polyphenols decrease it | Away from iron-rich meals |
| Calcium, phosphates | Decrease it | Dairy products and calcium supplements at a distance |
| Iron reserves | The main factor: the lower they are, the more absorption increases | It weighs more than meal composition |
In women with low iron reserves, 60 mg of iron was given either daily for 14 days or every other day for 28 days. Iron was better absorbed every other day, 21.8% versus 16.3%, and the total amount absorbed was higher, 175.3 mg versus 131 mg. Dividing the daily dose into two doses raised hepcidin, the hormone that slows absorption, without improving it.
Stoffel NU, Cercamondi CI, Brittenham G, et al. Lancet Haematol 2017;4(11):e524-e533. DOI: 10.1016/S2352-3026(17)30182-5
The same effect was found in anemic women, with 40 to 50% higher absorption when the dose was not preceded by a dose the previous day, with hepcidin remaining elevated for 24 hours. This schedule applies to high-dose iron supplements; it has not been studied with spirulina, whose iron content is much lower. Our guide when to take iron details the timing of intake.
Spirulina and vitamin B12: a false lead
Spirulina is often recommended to vegetarians for its iron but also for its vitamin B12. On this second point, studies are clear: most of its "B12" is an inactive form in humans. In spirulina tablets, 83% of B12-type compounds detected were pseudo-vitamin B12, and only 17% true B12.
In children deficient in B12, consumption of algae, including spirulina, raised B12 measured in the blood, but red blood cell volume, a sign of deficiency, worsened; fish or a B12 supplement improved it instead. For B12, a supplement remains the reference for vegetarians and vegans: see our guide to vitamin B12.
Quality and precautions
Spirulina is a cyanobacterium, a family some species of which produce toxins, microcystins. Monitoring of 623 spirulina samples produced by small French farms between 2013 and 2021 found an average content of 0.21 µg/g, with over 99% of samples remaining below the reference threshold of 1 µg/g. For 3 g per day, estimated exposure was more than four times below the tolerable dose set by the WHO.
The highest contaminations were found in other blue-green algae: on the Italian market, spirulina-only samples were not contaminated, unlike some Aphanizomenon-based products. On the metals side, cadmium and lead remained below European limits in analyzed products, but aluminum varied by origin: a 2024 study estimates that regular consumption of spirulina preparations could represent 11 to 176% of the weekly tolerable dose of aluminum.
| Situation | Why | Use |
|---|---|---|
| Autoimmune disease | Flare-ups of pemphigus and dermatomyositis reported with immunostimulant algae | Medical advice before any use |
| Pregnancy, breastfeeding | No trials | Medical advice |
| Phenylketonuria | Food very high in protein, therefore in phenylalanine | Avoid except on medical advice |
| Vegetarian, vegan | Does not cover B12 needs | B12 supplement |
| Confirmed iron deficiency | Effect not demonstrated on ferritin | Iron supplement and medical monitoring |
To limit these risks, it is better to choose spirulina from a traceable source, from organic farming, with the batch analyzed for toxins and metals.
The plan according to your situation
14 mg of iron in bisglycinate form, combined with 80 mg of vitamin C and 200 µg of vitamin B9, in one vegetable capsule per day, manufactured in France. Bisglycinate is a form of iron bound to glycine, associated in trials with fewer digestive issues than other forms. In case of confirmed deficiency, the dose and duration are to be determined with your doctor.
See Iron bisglycinateFor daily intake, also discover our organic spirulina.
Frequently asked questions
Is spirulina rich in iron?
Yes by weight: 35 to 146 mg of iron per 100 g in ten supplements analyzed, and up to 666 mg in one batch. But at usual doses, the intake remains modest: 0.7 to 2.9 mg per 2 g, or 4 tablets, and 3.5 to 14.6 mg per 10 g, depending on the product.
Is iron from spirulina well absorbed?
Data on intestinal cells are favorable for iron-enriched spirulina, and studies in rats are contradictory compared to iron sulfate. No isotopic measurement has been found in humans, and 78 to 93% of the iron in commercial products is in insoluble form.
Does spirulina raise ferritin levels?
No study demonstrates this: in children, average ferritin tended to decrease under spirulina. In a trial in adults with ulcerative colitis, serum iron increased, with no result reported for ferritin in the abstract.
Does spirulina correct anemia?
In children, the number of anemic children decreased by 11 under 2 g per day compared to 6 under placebo, without an increase in average hemoglobin. Hemoglobin increased by 3.4% in 17 cyclists, not in 20 others. No usable trial compares it to an iron supplement in case of iron deficiency anemia.
Spirulina or iron supplement in case of deficiency?
In case of proven deficiency, an iron supplement with medical follow-up: its absorption is measured by isotopes, and bisglycinate produced higher hemoglobin with fewer digestive problems in trials in pregnant women. Spirulina remains a dietary source of iron.
How to better absorb iron?
Combine a source of vitamin C with the meal, which helps mainly during the meal, and keep tea, coffee, dairy products, and calcium supplements away from the time of intake. Iron stores matter more than anything: the lower they are, the more absorption increases.
Should iron be taken every other day?
For supplements containing 60 to 200 mg of iron, isotopic studies suggest this: absorption increases from 16.3 to 21.8%, because hepcidin remains elevated 24 hours after intake. This schedule has not been studied with spirulina.
Does spirulina provide B12 to vegetarians?
Not reliably: 83% of its B12-type compounds are pseudo-vitamin B12, inactive in humans, and in deficient children, algae did not correct the red blood cell abnormality, unlike fish or a supplement.
Who should be cautious with spirulina?
People with autoimmune disease, with flare-ups having been reported, pregnant women, due to lack of trials, and people with phenylketonuria, as spirulina is very high in protein. It is better to have a traceable source, with a batch analyzed for toxins and metals.
How much spirulina per day?
The trials used 1 to 6 g per day, for 2 weeks to 3 months. A dose of 2 g, or 4 tablets, was used in two of these trials; it provides 0.7 to 2.9 mg of iron depending on the product.
Sources
The studies cited below were identified via PubMed.
- Isani G, Ferlizza E, Bertocchi M, et al. Iron content, iron speciation and phycocyanin of commercial samples of Arthrospira. International Journal of Molecular Sciences, 2022;23(22):13949. DOI
- Puyfoulhoux G, Rouanet JM, Besançon P, et al. Availability of iron from iron-enriched spirulina in an in vitro digestion model on Caco-2 cells. Journal of Agricultural and Food Chemistry, 2001;49(3):1625-1629. DOI
- Kapoor R, Mehta U. Iron status and growth of rats fed different dietary sources of iron. Plant Foods for Human Nutrition, 1993;44(1):29-34. DOI
- Gao F, Guo W, Zeng M, et al. Effect of microalgae used as an iron source on iron deficiency anemia in rats. Food & Function, 2019;10(2):723-732. DOI
- Selmi C, Leung PSC, Fischer L, et al. Effects of spirulina on anemia and immune function in seniors. Cellular & Molecular Immunology, 2011;8(3):248-254. DOI
- Barennes H, Houdart L, de Courville C, Barennes F. Spirulina as a daily nutritional supplement in disadvantaged young Cambodian children: a single-blind, placebo-controlled, crossover trial. BMC Pediatrics, 2022;22(1):701. DOI
- Moradi S, Foshati S, Poorbaferani F, et al. Effects of spirulina on serum iron, ferritin, anemia parameters and fecal occult blood in adults with ulcerative colitis: a randomized double-blind placebo-controlled trial. Clinical Nutrition ESPEN, 2023;57:755-763. DOI
- Ali Y, Aubeeluck R, Gurney T. Fourteen days of spirulina increase hemoglobin without improving performance in amateur cyclists: a randomized double-blind crossover trial. Journal of Dietary Supplements, 2024;21(3):261-280. DOI
- Gurney T, Brouner J, Spendiff O. Physiological effects of spirulina during effort at the lactate threshold in simulated altitude: a randomized trial. Journal of the International Society of Sports Nutrition, 2025;22(1):2498484. DOI
- Suliburska J, Szulińska M, Tinkov AA, Bogdański P. Effect of spirulina on calcium, magnesium, iron and zinc status in obese patients treated for hypertension. Biological Trace Element Research, 2016;173(1):1-6. DOI
- Hurrell R, Egli I. Iron bioavailability and dietary reference intakes. American Journal of Clinical Nutrition, 2010;91(5):1461S-1467S. DOI
- Cook JD, Reddy MB. Effect of vitamin C on non-heme iron absorption from a complete meal. American Journal of Clinical Nutrition, 2001;73(1):93-98. DOI
- Stoffel NU, Cercamondi CI, Brittenham G, et al. Iron absorption from supplements taken daily or every other day, in one or two doses, in women with low iron stores: two randomized trials. Lancet Haematology, 2017;4(11):e524-e533. DOI
- Stoffel NU, Zeder C, Brittenham GM, et al. Iron absorption from supplements is higher on alternate days than daily in women with iron deficiency anemia. Haematologica, 2020;105(5):1232-1239. DOI
- Fischer JAJ, Cherian AM, Bone JN, Karakochuk CD. Effects of iron bisglycinate on hemoglobin and ferritin in adults and children: systematic review and meta-analysis of randomized trials. Nutrition Reviews, 2023;81(8):904-920. DOI
- Milman N, Jønsson L, Dyre P, et al. 25 mg of iron as bisglycinate is as effective as 50 mg of iron sulfate for preventing iron deficiency and anemia during pregnancy: randomized trial. Journal of Perinatal Medicine, 2014;42(2):197-206. DOI
- Watanabe F, Katsura H, Takenaka S, et al. Pseudo-vitamin B12 is the predominant cobamide of a health food made from algae, spirulina tablets. Journal of Agricultural and Food Chemistry, 1999;47(11):4736-4741. DOI
- Dagnelie PC, van Staveren WA, van den Berg H. Vitamin B12 from algae does not appear to be bioavailable. American Journal of Clinical Nutrition, 1991;53(3):695-697. DOI
- Pinchart PE, Leruste A, Pasqualini V, Mastroleo F. Microcystins and cyanobacterial contaminants in small French spirulina productions. Toxins, 2023;15(6):354. DOI
- Vichi S, Lavorini P, Funari E, et al. Contamination by Microcystis and microcystins in blue-green algae dietary supplements on the Italian market. Food and Chemical Toxicology, 2012;50(12):4493-4499. DOI
- Varrà MO, Husáková L, Lanza GT, et al. Multi-elemental composition of plant preparations and probabilistic assessment of exposure to toxic metals. Food and Chemical Toxicology, 2024;188:114664. DOI
- Lee AN, Werth VP. Activation of autoimmunity following use of immunostimulant plant supplements. Archives of Dermatology, 2004;140(6):723-727. DOI
- Bax CE, Chakka S, Concha JSS, et al. Effects of immunostimulant plant supplements on autoimmune skin diseases. Journal of the American Academy of Dermatology, 2021;84(4):1051-1058. DOI
