Because spirulina is not FDA-regulated and is grown on the surface of water, individuals who ingest it can expose themselves to bacterial gastrointestinal diseases that cause vomiting and diarrhea, states WebMD. The high vitamin K in spirulina can render blood-thinning medications ineffective and increase stroke risk.
Spirulina is high in beta-carotene, which may increase lung cancer risks, reports WebMD. The potential for bacteria to be present in spirulina makes the supplement a health risk for individuals with weakened immune systems due to cancer therapies or conditions such as AIDS. Due to the unregulated nature of the product, heavy metal contamination resulting in liver toxicity and other adverse reactions are possible, adds Drugs.com. While spirulina is likely nontoxic to humans in normal doses of 1 to 10 grams a day, there is limited information.
A study in which spirulina was added to blood cells from the human immune system showed a marked increase in the production of cytokines, infection-fighting proteins used to ward off colds, reports WebMD. Research using chickens showed that spirulina stimulates infection-and-cancer-causing cells in their immune systems. Another study demonstrated that the algae acted as a natural antihistamine, alleviating allergies in rats. The documentation of spirulina’s cultivation is traceable back to the 16th century in Central America when Spanish explorers witnessed the Aztecs gathering a blue mud that is thought to have been spirulina. It is one of the few algae that thrive in high-salt alkaline water found in subtropical and tropical regions.