Euglena gracilis Suppresses Cold Symptoms in Healthy Individuals: A Double-Blind, Randomized, Placebo-Controlled Trial

The immune system functions to eliminate pathogens, such as viruses, and regulate physiological responses and pathways. General immunity is affected by various factors, including fatigue, stress, and aging. A weakened immune system reduces the ability of the body to eliminate pathogens, thereby increasing the risk of infections, including the common cold. Euglena gracilis is a microalga rich in various nutrients, including β-1,3-glucan paramylon, which aids in maintaining and regulating immune function. In the present study, we aimed to investigate the effects of E. gracilis administration on cold symptoms in healthy individuals. Euglena gracilis was administered orally in capsule form (once daily, in the morning) continuously for 8 weeks to healthy adult Japanese men and women. Evaluation of the effects of E. gracilis administration on alleviating cold symptoms revealed significantly fewer cumulative days with cold-like symptoms over 8 weeks in the E. gracilis group than those in the placebo group. Participants in the E. gracilis group also demonstrated significantly fewer severe cold-like symptoms, such as nasal congestion, sore throat, fatigue, and myalgia, than the placebo group in the second half of the trial (weeks 5–8). In conclusion, this study demonstrated that the continuous intake of E. gracilis could suppress cold-like symptoms. Moreover, the consumption of the test food under the conditions used in this study was deemed safe.