Spirulina (Arthrospira) is a non-toxic blue-green microalgae whose name is inspired by its spiral shape. Spirulina naturally thrives in warm, high-salt, alkaline (high pH) lakes. While it was originally believed to be a plant due to its photosynthetic capabilities, spirulina is now recognized as a type of cyanobacteria.^[4] For commercial use, spirulina is usually cultivated in controlled environments and subsequently dried and pulverized.^[5] There are several species of spirulina, but Arthrospira platensis is the one most frequently used in research and dietary supplements.^[6]

Spirulina is often touted as a “superfood” thanks to its impressive nutritional content, which includes proteins, essential amino acids, polyunsaturated fatty acids, vitamins, minerals, and various other bioactive compounds like carotenoids, chlorophyll, and phycocyanin. Accordingly, it has been used in a variety of contexts, ranging from undernourished populations to astronauts on space missions.^[4][7]

In vitro and animal research have suggested far-reaching benefits of spirulina, including antioxidant, anti-inflammatory, neuroprotective, anti-cancer, anti-viral, immune-modulating, hypoglycemic (blood-sugar-lowering), and cardioprotective properties.^[1] However, only a few of these effects have been observed in human clinical trials.

Clinical trials suggest that people who supplement with spirulina may see small but positive effects on various aspects of their cardiometabolic health, including improved lipid profiles,^[1][8] decreased blood pressure (particularly in those with high blood pressure),^[9] small reductions in body weight,^[10][11] and decreased fasting glucose.^[8][12]

Spirulina is often touted as a potent antioxidant and anti-inflammatory supplement. While this certainly is the case in pre-clinical research, human clinical trials have been mixed. Spirulina might increase total antioxidant capacity and superoxide dismutase activity, but no clear effects on inflammation have been found.^[13][14]

Spirulina is generally considered to be safe and well-tolerated. The most commonly reported side effects include gastrointestinal upset (e.g., abdominal cramps, diarrhea, nausea, vomiting), fatigue, dizziness, headache, and skin irritation (e.g., itching, rash).^[15]

There have been several case reports of more severe side effects with spirulina supplementation. These include rhabdomyolysis (a severe type of muscle breakdown),^[16] anaphylaxis (a life-threatening allergic reaction),^[17][18] liver toxicity,^[19] and the initiation or exacerbation of autoimmune skin conditions.^[20][21]

Although this has not been thoroughly investigated, spirulina may inhibit some cytochrome P450 enzymes, namely CYP1A2 and CYP2E1, which could lead to drug interactions.^[22]

Manufacturing practices and growth environments can influence the quality and safety of spirulina supplements. First, spirulina can accumulate heavy metals from its environment, raising the concern of contamination.^[23] One study that checked 25 brands of spirulina for mercury, nickel, and platinum found that none contained these heavy metals beyond acceptable levels,^[24] but choosing a spirulina supplement that is tested for heavy metals should still be a consideration. Second, contamination with other species of cyanobacteria could introduce potentially toxic compounds like microcystins.^[25]

Spirulina contains an abundance of bioactive compounds, including pigments, polyphenols, peptides, fatty acids, complex carbohydrates, vitamins, and minerals, which makes its mechanism of action fairly complicated and still incompletely understood. Phycocyanin, a blue-colored pigment that is structurally similar to bilirubin, is the most abundant protein in spirulina and is suggested to be the major active compound.^[26]

The antioxidant and anti-inflammatory properties of spirulina are the most thoroughly studied and likely arise from a variety of compounds including phycocyanin, carotenoids, chlorophyll, and vitamin E. Spirulina may increase the activity of antioxidant enzymes (e.g., superoxide dismutase), prevent lipid peroxidation, reduce NF-κB activity, and inhibit enzymes involved in the generation of reactive oxygen species and inflammatory compounds — nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and cyclooxygenase-2 (COX-2), respectively.^[26][14][27]

Spirulina may enhance cardiometabolic health through various mechanisms. It could potentially lower blood pressure by increasing nitric oxide production, thereby inhibiting angiotensin I converting enzyme, and/or simply due to its high potassium content (~18 mg per gram).^[9][4] Moreover, spirulina may influence lipid metabolism, reduce the digestion and absorption of dietary fats and carbohydrates, promote cholesterol excretion, increase satiety, and stimulate insulin secretion.^{[28][29][1][30]}