Wang J. & al: Vitamin A equivalence of spirulina β-carotene in Chinese adults as assessed by using a stable-isotope reference method, The American Journal of Clinical Nutrition, Volume 87, Issue 6, 1 June 2008, Pages 1730-1737.
Yang Y. & al: In vitro and in vivo safety assessment of edible blue-green algae, Nostoc commune var. sphaeroides Kützing and Spirulina plantensis. Food and chemical toxicology: an international journal published for the British Industrial Biological Research Association. 2011;49(7):1560-1564. doi:10.1016/j.fct.2011.03.052.