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1. Introduction
Spirulina is a microscopic and filamentous cyanobacterium that derives its name from the spiral or helical nature of its filaments. It has a long history of use as food and it has been reported that it has been used during the Aztec civilization [1]. Spirulina refers to the dried biomass of Arthrospira platensis, an oxygenic photosynthetic bacterium found worldwide in fresh and marine waters. This alga represents an important staple diet in humans and has been used as a source of protein and vitamin supplement in humans without any significant side-effects. Apart from the high (up to 70%) content of protein, it also contains vitamins, especially B12 and provitamin A (β-carotenes), and minerals, especially iron. It is also rich in phenolic acids, tocopherols and γ-linolenic acid [1]. Spirulina lacks cellulose cell walls and therefore it can be easily digested [1].
Many toxicological studies have proven Spirulina's safety. Spirulina now belongs to the substances that are listed by the US Food and Drug Administration under the category Generally Recognized as Safe (GRAS) [2–6]. Spirulina is relatively easy to cultivate but flourishes only in alkaline lakes with an extremely high pH and in large outdoor ponds under controlled conditions. There are only a few areas worldwide that have the ideal sunny climate for production of this alga, including Greece (Nigrita, Serres), Japan, India, United States and Spain. Currently, Spirulina can be found in health food stores and is sold mainly as a dietary supplement in the form of health drinks or tablets. Microalgae have been used for more than 10 years as dietary supplements without significant side-effects [7]. The aims of this review are to summarize the mechanisms of action, highlight the potential effects of this alga in humans and address current and possible future clinical applications, based mainly on in vivo studies and a few well-designed in vitro studies and the highest levels of evidence available in the literature.
2. Evidence-Based Applications of Spirulina
2.1. Spirulina and Chronic Fatigue
Spirulina has been promoted as “the food of the future" with “exceptional constituents" that contribute to high energy levels. A few of these constituents such as polysaccharides (Rhamnose and Glycogen) and essential fat (GLA) are absorbed easily...