The species A. maxima and A. platensis were once classified in the genus Spirulina. The common name, spirulina, refers to the dried biomass of A. platensis, which belongs to photosynthetic bacteria that cover the groups Cyanobacteria and Prochlorophyta. Scientifically, a distinction exists between spirulina and the genus Arthrospira. Species of Arthrospira have been isolated from alkaline brackish and saline waters in tropical and subtropical regions. Among the various species included in the genus Arthrospira, A. platensis is the most widely distributed and is mainly found in Africa, but also in Asia. A. maxima is believed to be found in California and Mexico. The term spirulina remains in use for historical reasons.
Arthrospira species are free-floating, filamentous cyanobacteria characterized by cylindrical, multicellular trichomes in an open left-handed helix. They occur naturally in tropical and subtropical lakes with high pH and high concentrations of carbonate and bicarbonate.A. platensis occurs in Africa, Asia, and South America, whereas A. maxima is confined to Central America. Most cultivated spirulina is produced in open-channel raceway ponds, with paddle wheels used to agitate the water.
Spirulina thrives at a pH around 8.5 and above and a temperature around 30 °C (86 °F). They are autotrophic, meaning that they are able to make their own food, and do not need a living energy or organic carbon source. In addition, a nutrient feed for growing it is:
†Percentages are roughly approximated using US recommendations for adults. Source: USDA FoodData Central
Spirulina was a food source for the Aztecs and other Mesoamericans until the 16th century; the harvest from Lake Texcoco in Mexico and subsequent sale as cakes were described by one of Cortés' soldiers. The Aztecs called it tecuitlatl.
Spirulina was found in abundance at Lake Texcoco by French researchers in the 1960s, but no reference to its use by the Aztecs as a daily food source was made after the 16th century, probably because of the draining of the surrounding lakes for agriculture and urban development. The topic of tecuitlatl, which was discovered in 1520, was not mentioned again until 1940, when the Belgian phycologist Pierre Dangeard mentioned a cake called dihe consumed by the Kanembu tribe, who harvest it from Lake Chad in the African nation of Chad. Dangeard studied the dihe samples and found it to be a dried puree of the spring form of the blue-green algae from the lake. The dihe is used to make broths for meals, and also sold in markets. The spirulina is harvested from small lakes and ponds around Lake Chad.
During 1964 and 1965, the botanist Jean Leonard confirmed that dihe is made up of spirulina, and later studied a bloom of algae in a sodium hydroxide production facility. As a result, the first systematic and detailed study of the growth requirements and physiology of spirulina was performed as a basis for establishing large-scale production in the 1970s.
Spirulina contains no vitamin B12 naturally (see table), and spirulina supplements are not considered to be a reliable source of vitamin B12, as they contain predominantly pseudovitamin B12 (Coα-[α-(7-adenyl)]-Coβ-cyanocobamide), which is biologically inactive in humans. In a 2009 position paper on vegetarian diets, the American Dietetic Association stated that spirulina is not a reliable source of active vitamin B12. The medical literature similarly advises that spirulina is unsuitable as a source of B12.
Animals and aquaculture
Various studies on spirulina as an alternative feed for animal and aquaculture have been done. Spirulina can be fed up to 10% for poultry  and less than 4% for quail. Increase in the spirulina content up to 40 g/kg (0.64 oz/lb) for 16 days in 21-day-old broiler male chicks, resulted in yellow and red coloration of flesh and this may be due to the accumulation of the yellow pigment, zeaxanthin. Pigs and rabbits can receive up to 10% of the feed and increase in the spirulina content in cattle resulted in increase in milk yield and weight. Spirulina as an alternative feedstock and immune booster for big-mouth buffalo, milk fish, cultured striped jack, carp, red sea bream, tilapia, catfish, yellow tail, zebrafish, shrimp, and abalone was established and up to 2% spirulina per day in aquaculture feed can be safely recommended.
According to the U.S. National Institutes of Health, scientific evidence is insufficient to recommend spirulina supplementation for any human condition, and more research is needed to clarify whether consumption yields any benefits. Administration of spirulina has been investigated as a way to control glucose in people with diabetes, but the European Food Safety Authority rejected those claims in 2013. Spirulina has been studied as a potential nutritional supplement for adults and children affected by HIV, but there was no conclusive effect on risk of death, body weight, or immune response.
Spirulina is a form of cyanobacterium, some of which were found to produce toxins, such as microcystins. Some spirulina supplements have been found to be contaminated with microcystins, albeit at levels below the limit set by the Oregon Health Department. Microcystins can cause gastrointestinal upset, such as diarrhea, flatulence, headache, muscle pain, facial flushing, and sweating. If used chronically, liver damage may occur. The effects of chronic exposure to even low levels of microcystins are a concern due to the risk of toxicity to several organ systems.
These toxic compounds are not produced by spirulina itself, but may occur as a result of contamination of spirulina batches with other, toxin-producing, blue-green algae. Because spirulina is considered a dietary supplement in the U.S., no active, industry-wide regulation of its production occurs and no enforced safety standards exist for its production or purity. The U.S. National Institutes of Health describes spirulina supplements as "possibly safe", provided they are free of microcystin contamination, but "likely unsafe" (especially for children) if contaminated. Given the lack of regulatory standards in the U.S., some public-health researchers have raised the concern that consumers cannot be certain that spirulina and other blue-green algae supplements are free of contamination. In 1999, Health Canada found that one sample of spirulina was microcystin-free. ("...0/10 samples of Spirulina contained microcystins.")
Heavy-metal contamination of spirulina supplements has also raised concern. The Chinese State Food and Drug Administration reported that lead, mercury, and arsenic contamination was widespread in spirulina supplements marketed in China. One study reported the presence of lead up to 5.1 ppm in a sample from a commercial supplement. Spirulina doses of 10 to 19 grams per day over several months have been used safely.
Safety issues for certain target groups
Like all protein-rich foods, spirulina contains the essential amino acid phenylalanine (2.6–4.1 g/100 g), which should be avoided by people who have phenylketonuria, a rare genetic disorder that prevents the body from metabolizing phenylalanine, which then builds up in the brain, causing damage.
Spirulina contaminated with microcystins has various potential toxicity, especially to children and pregnant women, including liver damage, shock, and death.
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