Blue-Green Algae (AFA): Nutrients, What Research Shows and Safety

AFA is short for Aphanizomenon flos-aquae, a blue-green alga (a cyanobacterium, a kind of bacteria that makes its own food from light). The AFA sold as a supplement is mostly harvested wild from Upper Klamath Lake in Oregon, then dried and sold as powder or capsules. [1] [2] This page treats AFA as a supplement product, not a sea vegetable. It separates safety facts, lab findings and the little we know from people.

Read this first

• Contamination is the main issue. AFA grows in the same lake as Microcystis aeruginosa, a toxic alga that makes microcystins (liver toxins). A 2000 study found microcystins in 85 of 87 blue-green algae products tested, and 63 of them (72%) were above Oregon's limit of 1 microgram per gram. [1] A 2018 test of 51 U.S. AFA products found about half had detectable microcystin and four were above 1 microgram per gram. [2] Quality varies between products, and you cannot see it on the label.
• Human evidence is thin. In the sources we read, we found no human trial of AFA supplements. Nearly all AFA research is in cells, tissue or animals. [5] [6] [7] [8]
• B12 claims: AFA biomass contains a small amount of vitamin B12 in one lab analysis, but nobody has shown that people absorb it, and the authors suggest it may come from bacteria living with the alga. [5] Do not rely on AFA for B12.
• Ask a clinician first if you are pregnant, breastfeeding, have PKU, an autoimmune disease or a liver problem. For these groups we found no supporting safety data, which is not the same as proof of safety.
• Serious allergic reactions have been reported with blue-green algae supplements. For trouble breathing or swelling of the face or throat, call 911 (or your local emergency number). [3]

What is in it (USDA values)

No USDA entry for this food. USDA FoodData Central (SR Legacy) has no record for AFA, so there are no USDA values to show. We did not find an official composition table for AFA in the sources we read. One lab study measured vitamin B12 at about 0.4 to 0.5 micrograms per gram of dried AFA biomass and said it is likely linked to bacteria living alongside the alga. [5] The same study did not test whether people can use it. Product labels differ by brand and harvest, so use the label of your own product.

Plant compounds: an AFA extract and purified C-phycocyanin (the blue pigment-protein) were tested in a 2025 lab study that measured antioxidant activity in a test tube and toxicity to cancer cells in dishes. [9] That is laboratory evidence only. It does not show an effect in people.

What research says

Supplement vs food. AFA is not eaten like a vegetable. It is a dried powder or capsule product, and only the supplement form was in the studies above. Spirulina and chlorella are different organisms with their own pages: see spirulina and chlorella.

How much is a normal serving

There is no official serving size for AFA from USDA, NHS, EFSA or another body in the sources we read. Serving sizes on products vary, which the 2018 test authors said prevented a full estimate of how much microcystin a consumer takes in. [2] This is information, not a prescription. Ask a clinician or pharmacist.

Safety, allergy and medicines

• Microcystins: these are liver toxins from Microcystis. MSK describes them as cyclic peptides that harm the liver, and says contamination of blue-green algae products is uncommon but can cause liver damage, kidney failure and nerve damage. [3] Oregon set 1 microgram per gram for products; the 2000 study found 72% of tested products above it. [1] Most products in the 2018 test were at or below 1 microgram per gram, which the authors read as manufacturers using that figure as a specification. [2]
• Toxin genes differ by strain: a 2026 genome study found toxin gene clusters in about 7.3% of the 161 related genomes it analyzed. [5] This is a reminder that strains differ.
• Allergy: MSK lists anaphylaxis among reported adverse effects of blue-green algae supplements. [3] Phycocyanin and a linker protein were identified as allergens in a related blue-green alga, Microcystis, in patient blood samples. [4]
• Muscle damage and newborn case: MSK reports a case of rhabdomyolysis (severe muscle breakdown) after a month of spirulina and a newborn with seizures linked to the mother's long-term spirulina use. These involved spirulina, not AFA. [3]
• Pregnancy and breastfeeding: LactMed says there is no lactation-specific safety data for these algae, and that products from uncontrolled sources may carry contaminants. [11] We did not find an official statement on AFA in pregnancy.
• PKU (phenylketonuria): Proper evidence not found in the sources we read on the phenylalanine content of AFA. People with PKU should ask their metabolic dietitian.
• Autoimmune disease: Proper evidence not found in the sources we read. MSK mentions immune effects such as more natural killer cells, but says this does not prove benefit. [3] Immune-stimulating products are a reason to ask a specialist.
• Medicines: MSK says spirulina inhibits two liver enzymes (CYP1A2 and CYP2E1), with unknown clinical meaning. We found nothing like it for AFA. [3]

Choosing, storing and food safety

• Look for a product with a recent independent test for microcystin. We did not read a source that rates specific brands, and a label claim does not replace a lab report.
• See our guide: Blue-green algae supplements: microcystins and quality.
• Storage advice for AFA products: Proper evidence not found in the sources we read. Follow the label.

Related pages

• Blue-green algae supplements: microcystins and quality
• Spirulina
• Chlorella
• Spirulina vs chlorella
• Seaweed and vitamin B12 claims checked
• Autoimmune conditions and immune-stimulating products