The supplement called spirulina consists of one or more members of a family of blue-green algae. The name was inspired by the spiral shapes in which these plants array themselves as they grow.1 Other blue-green algae products are also available on the market, and they are discussed in this article as well.

Spirulina grows in the wild in salty lakes in Mexico and on the African continent. It reproduces quickly, and because the individual plants tend to stick together, it is easy to harvest. Records of the Spanish conquistadors suggest that the Aztecs used spirulina as a food source; we also know that the Kanembu people of Central Africa harvested it from what is now called Lake Chad.

This plant contains high levels of  various B vitamins, beta-carotene, other carotenoids, and minerals, including calcium, iron, magnesium, manganese, potassium, and zinc. It is also a source of gamma-linolenic acid (GLA) . Spirulina is a rich source of protein—dried spirulina contains up to 70% protein by weight 2 —but you'd have to eat an awful lot of spirulina capsules to obtain a significant amount of protein this way. Spirulina also contains vitamin B12, a nutrient otherwise found almost exclusively in animal foods. However, there's a catch: the B 12in spirulina is not absorbable.3

Spirulina has not been proven effective for any medical condition, and there are significant safety concerns involving all forms of blue-green algae (see Safety Issues).

Unless you live within 35 degrees of the equator and on the shores of an alkaline lake, you will have difficulty finding spirulina anywhere but in a health food store. Most carry a number of brands of spirulina that has been dried and processed into powder or tablets.