Records show that spirulina was used traditionally as a food by the Aztecs in Mexico and has been used by the Kanembu people of North Africa since at least the 16th century. In Africa, spirulina — locally called dihé — is harvested from various alkaline lakes surrounding Lake Chad. Similarly, in Mexico before the Spanish conquest, spirulina — locally called tecuitlatl — was harvested from Lake Texcoco, where it grew abundantly. In both cases, the spirulina is gathered from the lakes and left to try in the sun, after which it can be broken into small pieces to be sold as food.^[26][31][32]

Spirulina is sometimes promoted for people following a plant-based diet because of its protein and vitamin B12 content. While it may have a role in this context, the value is often overstated.

Based on its dry weight, spirulina is about 60 to 75% protein (~65 g per 100 g dried spirulina) and contains all of the essential amino acids.^[33] This is notable for a protein source that is not animal-based, but spirulina is usually only dosed up to 10 grams daily, which would provide 7.5 grams of protein at best. While this might help someone reach their protein goals, it only fulfills a fraction of daily protein requirements.

On average, a 10-gram dose of spirulina might contain around 20 micrograms of vitamin B12.^[4] However, the majority of vitamin B12 in spirulina is actually a type of pseudovitamin B12 that is not readily usable by the human body.^[34] One study found that 83% of the vitamin B12 in spirulina was in the pseudovitamin form, which would reduce the usable amount of vitamin B12 in a 10-gram dose from 20 micrograms to 3.4 micrograms. While 3.4 micrograms is a much smaller dose than that normally found in vitamin B12 supplements, it technically does meet the Recommended Daily Allowances (RDAs) for all age and sex groups.^[35]

Spirulina may have some beneficial effects on exercise performance, but current evidence is mixed and inconclusive.

Preliminary research suggests that spirulina may have a positive effect on endurance training (e.g., running, cycling) by lowering fatigue and increasing power output, possibly through reductions in oxidative stress and increases in hemoglobin levels and oxygen uptake.^{[36][37][38][2]}

In terms of recovery, the majority of research suggests that spirulina has no impact on post-exercise muscle recovery, including delayed onset muscle soreness.^[2] However, in athletes with an insufficient intake of dietary antioxidants, spirulina may reduce muscle oxidative damage and accelerate recovery.^[38][2]

While the antioxidant effects of spirulina in clinical trials are generally mixed, it’s also important to consider that antioxidant supplementation during or after exercise may blunt the body's natural responses required for muscle adaptation and growth.^[39]

Spirulina has shown some promise for reducing symptoms of allergic rhinitis, but research is still at an early stage.

A few studies have found that compared to a placebo, spirulina reduced symptoms of allergic rhinitis.^[40][41] Interestingly, a randomized controlled trial found that spirulina supplementation given daily for two months was as effective as cetirizine — a commonly-used allergy medication — at reducing symptoms of nasal itching and sneezing and more effective than cetirizine at reducing rhinorrhea (runny nose) and nasal congestion.^[3]

This effect may be due to how spirulina interacts with the immune system. More specifically, spirulina may reduce levels of interleukin 4 and prevent the release of histamine from mast cells.^{[42][3][43][44]}

Spirulina has demonstrated anticancer properties in in vitro and animal studies, but human clinical trials are scarce.

Spirulina contains several compounds that have individually been found to have anticancer properties, and of these, phycocyanin appears to have the greatest potential. Phycocyanin extracted from spirulina has been shown in pre-clinical research to induce cell death (apoptosis) in a variety of cancer cell lines and prevent the formation of new blood vessels (angiogenesis), effectively inhibiting the proliferation of cancer cells.^[45]

Additionally, some research suggests that spirulina may enhance natural killer cell activity, which could have an antitumor effect.^[46][47] Several clinical trials suggest that spirulina supplementation may reverse precancerous lesions in the mouth.^{[48][49][50][51]}

Spirulina contains compounds with antibacterial properties, as well as complex carbohydrates and polyphenols capable of stimulating the growth of certain microbes. Preclinical research suggests that spirulina may inhibit the growth of some potentially pathogenic microorganisms (e.g., Escherichia coli, Staphylococcus aureus, Candida albicans) while supporting the growth of microorganisms generally thought to be beneficial (e.g., those in the Lactobacillus and Bifidobacteria genera).^[6]

While this suggests that spirulina has the potential to beneficially impact the gut microbiome, there is currently no research exploring this in humans.

Spirulina supplementation has been shown in a variety of populations to improve markers of iron deficiency anemia, including increased levels of hemoglobin, a higher red blood cell count, and an increased hematocrit.^{[52][53][54][37][55]}

This effect could relate to spirulina’s highly bioavailable iron (although there are only ~5 mg of iron per 10 grams of dried spirulina),^[4] but the predominant protein in spirulina, phycocyanin, may also stimulate red blood cell production.^[56]

There currently isn’t enough research to suggest that spirulina might be a replacement for standard anemia treatments such as iron supplementation. Additionally, the nutritional content of spirulina can vary depending on the cultivation and processing techniques used, which could alter its effectiveness for anemia.^[27]

In animal studies, spirulina has demonstrated promise for the management or prevention of nonalcoholic fatty liver disease (NAFLD), but more research in humans is needed to confirm this effect.

In mice, spirulina has demonstrated the ability to both prevent and reduce the incidence of fatty liver in mouse models of NAFLD, although these studies have generally used much higher doses of spirulina than are recommended for humans.^[57][58][59] In people with NAFLD, both a series of case studies including three people and an uncontrolled study including fifteen people found that spirulina supplementation significantly reduced liver enzymes. Nevertheless, ultrasound assessments didn’t consistently find improvements in NAFLD.^[60][61]