Spirulina and Chlorella: Properties of Superfoods and How to Use Algae in Your Daily Diet

Spirulina and chlorella are on the same shelf, sold under the common superfoods slogan, and most descriptions treat them interchangeably. They are two different organisms, and a significant part of the promises on the label looks different when you look at the source data. The American USDA FoodData Central reports 57.5 g of protein per 100 g of dried spirulina, but the actual serving is 3-5 g per day, so less protein enters the diet than from one egg. The same goes for vitamin B12, detoxing heavy metals, and the list of anti-inflammatory properties. Below you will find what results from published studies: where the evidence is solid, where it comes from one small trial, and where there is none at all.

KEY INFORMATION
• Vitamin B12 in spirulina is 83% pseudovitamin, inactive in humans (Watanabe et al., J Agric Food Chem, 1999).
• USDA FoodData Central reports 0.0 micrograms of vitamin B12 per 100 g of dried spirulina.
• Microcystins were detected in all five tested spirulina products (Rhoades et al., Microorganisms, 2023).
• There is no human study showing that chlorella removes heavy metals from the body.

What is the difference between spirulina and chlorella?

Spirulina is a cyanobacterium, a bacterium without a cell nucleus, while chlorella is a single-celled green alga with a nucleus and a hard cellulose wall. This difference has practical consequences: chlorella, without mechanical breakdown of the wall, passes through the intestine largely undigested, while spirulina breaks down on its own.

Both have entered supplements through the same marketing route, but they have different profiles. Spirulina owes its color to phycocyanin, a blue protein pigment, while chlorella is green from chlorophyll. Karkos et al. (Evidence-Based Complementary and Alternative Medicine, 2011) gathered the available applications of spirulina in humans at that time and summarized them as promising but based on few randomized trials. Fifteen years later, this assessment has aged less than one might think.

The terminology can be misleading. “Alga” in the case of spirulina is a shorthand, as Arthrospira platensis is a photosynthetic bacterium related to cyanobacteria that bloom in lakes during summer. This is not a taxonomic curiosity. This is why microcystins, which are liver-damaging cyanobacterial toxins, are mentioned with spirulina, but not with chlorella.

How much spirulina actually enters the diet in one serving?

Significantly less than the label suggests. USDA FoodData Central reports 57.5 g of protein per 100 g of dried spirulina, but the serving recommended by manufacturers is usually 3-5 g per day. At 5 g, you get about 2.9 g of protein, which is less than from one egg.

The same mechanism applies to other ingredients. The number per 100 g is impressive because no one eats 100 g of algae powder. The table below converts USDA data (SR Legacy, item 170495, dried spirulina) into a serving that is actually consumed.

There is an additional caveat with iron. Masten Rutar et al. (Foods, 2022) examined spirulina products from the Slovenian market and found that the declared iron content can be high, but the element mainly occurs as iron cation, poorly absorbed from the digestive tract. In the same study, 86.7% of declared elemental content did not match measurements.

Is spirulina a source of vitamin B12 for vegans?

No. Spirulina primarily contains pseudovitamin B12, an analog that the human body does not utilize. USDA FoodData Central reports 0.0 micrograms of vitamin B12 per 100 g of dried spirulina. Treating it as a safeguard against deficiency is the most serious mistake in this matter.

Watanabe et al. (Journal of Agricultural and Food Chemistry, 1999) broke down spirulina tablets into their components using two methods. The microbiological determination yielded results 6-9 times higher than the method based on binding to the intrinsic factor, as the former also counts inactive analogs. Of the isolated compounds, 83% was pseudovitamin B12, and only 17% was true cobalamin. This work has been cited for a quarter of a century and has not been challenged.

The consequence is twofold. Deficiency is not compensated, and inactive analogs can inflate the result of a regular B12 serum test, so the control test looks correct despite a real deficit. A person on a plant-based diet relying on spirulina may go for years without knowing they have a problem. More reliable are measurements of methylmalonic acid or holotranscobalamin.

Chlorella performs better here, but the evidence is thin. Merchant et al. (Journal of Medicinal Food, 2015) administered 9 g of chlorella daily for 60 days to seventeen vegans and vegetarians with elevated methylmalonic acid levels. The marker dropped by an average of about 34%. The study was open-label, without a control group and without blinding, on seventeen individuals. This is a signal, not a resolution.

Does chlorella remove heavy metals from the body?

There is no human study that shows this. The works cited in advertisements concern other substances: dioxins with chlorella and arsenic with spirulina. Dioxins are persistent organic pollutants, arsenic is a metalloid. None of these studies measured lead, mercury, or cadmium in humans.

The most frequently cited work under the detox slogan is Nakano et al. (Chemosphere, 2005). It measured dioxin levels in the milk of 44 pregnant Japanese women, and 23 of them were instructed to take a Chlorella pyrenoidosa supplement. The total toxic equivalency in the mothers’ milk was about 30% lower in the group with chlorella (p=0.0113). However, it was not a randomized or blinded trial, and the measured endpoint remained dioxins.

On the side of spirulina stands Misbahuddin et al. (Clinical Toxicology, 2006), a randomized placebo trial with 41 patients with chronic arsenic poisoning in Bangladesh. Twenty-four individuals received 250 mg of spirulina extract with 2 mg of zinc twice daily for 16 weeks, while seventeen received placebo. Hair samples showed a 47.1% reduction in arsenic. This is one small study, on extract rather than powder, in a population drinking contaminated water. Transferring this result to detoxifying a healthy person in Poland has no basis. More about what popular detox treatments actually do can be found in the post about detox without fasting.

What contaminants can end up in algae supplements?

Microcystins and pathogenic bacteria, and in newer analyses, also pharmaceutical residues. Spirulina is usually grown in open ponds, which can be contaminated by other cyanobacteria, including species that produce liver toxins. When choosing a supplement, quality control is more practically significant than the vitamin composition on the label.

Rhoades et al. (Microorganisms, 2023) examined five commercially available spirulina products, two supplements, and three food items. Microcystins were detected in all five, at levels where consumers may exceed the recommended daily limit. Samples also contained Bacillus cereus and Klebsiella pneumoniae. The authors directly link this to the production method in open tanks.

With metals, the situation is better. Sochacka et al. (International Journal of Molecular Sciences, 2025) analyzed 52 spirulina and chlorella products, 29 conventional and 23 organic. All were within EU limits for toxic metals, while the calculated aluminum content in the tolerated weekly intake was deemed concerning. They also detected pharmaceutical residues: caffeine, metronidazole, and carbamazepine. Organic products did not perform better than conventional ones.

A separate issue is iodine, which appears reflexively in algae descriptions. The problem concerns macroalgae like kombu or wakame, not freshwater spirulina and chlorella. With them, pay attention to microcystins and aluminum, not the thyroid.

Who should avoid spirulina and chlorella?

People with phenylketonuria and those with autoimmune diseases, the latter after consulting a doctor. Spirulina contains 2.78 g of phenylalanine per 100 g according to USDA, so a 5 g serving contributes about 139 mg. In a low-phenylalanine diet, this is a number that needs to be accounted for, not ignored.

Immunostimulation by algae is documented, and this raises concerns. Kwak et al. (Nutrition Journal, 2012) administered 5 g of chlorella daily for 8 weeks in a randomized placebo trial involving 51 healthy individuals. NK cell activity increased, as did levels of gamma interferon and interleukin 1 beta. In a healthy person, this is a desirable effect. What the same stimulus does in Hashimoto’s, lupus, or psoriasis has not been studied.

There have also been reports of isolated adverse events. Konno et al. (Rinsho Shinkeigaku, 2011) presented a case of inflammatory myopathy with extensive rash after supplements containing spirulina. A single case report does not prove a causal relationship, but it shows that the product is not biologically inert.

There is practically no data on safety during pregnancy and breastfeeding, and no one has studied interactions with medications taken regularly. Therefore, we do not provide doses as recommendations. The numbers from the cited works describe research protocols, not recommendations for the reader.

What do meta-analyses show about lipids and blood pressure?

The direction of changes is consistent, but the evidence is based on small and short trials. The largest lipid meta-analysis included 20 studies and 1076 participants, while the blood pressure meta-analysis included only 5 studies and 230 individuals. This is too little to speak of an established clinical effect.

Rahnama et al. (Pharmacological Research, 2023) collected 20 studies in 23 arms involving 1076 individuals and assessed them using the GRADE system. Spirulina lowered total cholesterol, LDL fraction, and triglycerides (standardized mean difference of -0.6, confidence interval from -0.9 to -0.2) and raised HDL fraction by 0.3. However, for HDL, the lower end of the confidence interval is exactly 0.0, meaning the result barely touches the significance threshold, and one less study would make it disappear. An earlier meta-analysis Serban et al. (Clinical Nutrition, 2016) included only 7 trials and reported decreases of 41-47 mg/dl. Such large effects with so few studies are more a reason for caution than enthusiasm.

For blood pressure, Machowiec et al. (Nutrients, 2021) summarized 5 randomized trials with 230 participants, doses from 1 to 8 g daily, and durations from 2 to 12 weeks. Systolic blood pressure decreased by 4.59 mmHg with high heterogeneity of results (I-squared 65%), diastolic by 7.02 mmHg with heterogeneity of 11%. It is worth looking at the ends of the confidence interval, not just the average: for systolic blood pressure, it ranges from -8.20 to -0.99 mmHg, so the lower limit describes a decrease that the patient would not notice. The effect is mainly seen in a subgroup of people with hypertension.

In allergic rhinitis, there is one cited trial with a double-blind design: Cingi et al. (European Archives of Oto-Rhino-Laryngology, 2008) noted improvement in symptoms compared to placebo. One study does not close the case.

How to incorporate algae into your diet without disappointment?

By treating them as an addition, not as a pillar of the diet. A serving of 3-5 g contributes a few percent of daily protein and iron needs, so the real contribution is small. Choosing a product with documented quality control matters more than the regularity of intake.

Several things follow directly from the biology of these organisms. Chlorella must have its cell wall broken; otherwise, most of the cell’s contents pass through the intestine untouched. Do not cook spirulina, as phycocyanin and proteins do not withstand high temperatures, so add the powder to cold or lukewarm dishes. Non-heme iron from algae is better absorbed in the presence of vitamin C and decreases with coffee and tea.

Phycocyanin is sometimes described as a natural anti-inflammatory agent. The basis is the work of Reddy et al. (Biochemical and Biophysical Research Communications, 2000), in which this pigment selectively inhibited the COX-2 enzyme at a concentration that reduced half of its activity, equal to 180 nanomoles per liter in a test on isolated enzyme and 80 nanomoles per liter in a test on whole blood. Measurements were made on material outside the body, and no one has repeated them in humans, and concentrations from a test tube do not translate to a serving of powder added to a smoothie.

In sports, the data is equally sparse and concerns a narrow slice of effort. Gurney and Spendiff (European Journal of Applied Physiology, 2020) administered 6 g of spirulina daily for 7 days to eleven men not training on a hand ergometer, in an alternating blinded scheme. Hemoglobin after spirulina was 154.5 g/l compared to 144.1 g/l after placebo, and oxygen consumption and heart rate during thirty minutes of submaximal effort were lower. Time to fatigue did not change. They only studied cranking with arms, so transferring this to running or strength training is speculative, and eleven individuals and a week of supplementation is too little even for conclusions about the ergometer itself.

We noticed while organizing product descriptions that the composition is given per 100 g, while the dosage is given per serving. These two numbers are practically divided by twenty, so always compare on the same unit.

Frequently Asked Questions

Does spirulina contain vitamin B12?

No, in a form usable by humans. Watanabe et al. (Journal of Agricultural and Food Chemistry, 1999) showed that 83% of compounds isolated from spirulina tablets are pseudovitamin B12, and only 17% is true cobalamin. USDA FoodData Central reports 0.0 micrograms of vitamin B12 per 100 g of dried spirulina.

What is the difference between chlorella and spirulina?

Spirulina is a cyanobacterium, a photosynthetic bacterium without a cell nucleus. Chlorella is a single-celled green alga with a nucleus and a hard cellulose wall that must be mechanically broken for the cell’s contents to be accessible. This difference also leads to the risk of microcystins, which concern spirulina but not chlorella.

Does chlorella detoxify the body from heavy metals?

There is no human study that shows this. The most frequently cited work (Nakano et al., Chemosphere, 2005) measured dioxins in the milk of 44 pregnant Japanese women, not lead, mercury, or cadmium. Dioxins are persistent organic pollutants, not metals.

Is spirulina safe for autoimmune diseases?

This has not been studied. Kwak et al. (Nutrition Journal, 2012) showed that 5 g of chlorella daily for 8 weeks increases NK cell activity and gamma interferon levels in healthy individuals. The effect of such stimulation in Hashimoto’s or lupus has not been studied. Make a decision with your doctor.

How to recognize a high-quality algae supplement?

By the available certificate of analysis covering microcystins, metals, and microbiology. Rhoades et al. (Microorganisms, 2023) detected microcystins in all five tested spirulina products. Masten Rutar et al. (Foods, 2022) found that 86.7% of declared elemental content did not match measurements.

Does spirulina lower cholesterol and blood pressure?

Meta-analyses show a decrease, but they are based on small samples. Rahnama et al. (Pharmacological Research, 2023) collected 20 studies with 1076 participants. Machowiec et al. (Nutrients, 2021) summarized 5 studies with 230 people, noting a decrease in systolic blood pressure of 4.59 mmHg with high heterogeneity of results.

Spirulina and chlorella products can be found in the supplements section, and we described the broader context of a plant-based diet in the post about supplements for vegetarians and vegans.

This article is for informational and educational purposes and does not constitute medical advice. Before starting supplementation, consult your doctor, especially if you are taking medications regularly, are pregnant or breastfeeding, or have chronic illnesses.

Author: Michał Waluk · Published: 2026-06-22 · Updated: 2026-08-16