Effects of Oral Ingestion of L-Ornithine on Mental Stress and Fatigue Based on the Trier Social Stress Test in Healthy Humans: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Trial.

With changes in the social environment typified by COVID-19, an increasing number of people are suffering from mental stress in interpersonal relationships and the resulting fatigue in recent years. L-ornithine oral ingestion reportedly suppresses the secretion of cortisol, a stress marker, through the hypothalamic-pituitary-adrenal (HPA) axis. However, there is insufficient research to determine whether L-ornithine exerts an ameliorative effect on social stress. Therefore, in this study, we investigated how L-ornithine affects mental stress and fatigue after social stress in healthy participants. We randomly assigned 65 participants into two groups, ingesting orally either 1600 mg of L-ornithine or a placebo for 7 days. On the day of the Trier Social Stress Test (TSST), participants took test products one hour before the testing. We evaluated the effects on saliva cortisol and mood states, including fatigue. While L-ornithine did not affect saliva cortisol levels, it significantly improved the fatigue-inertia and anger-hostility scales of the Profile of Mood States on the morning after the TSST in the L-ornithine group compared to the placebo group. In conclusion, L-ornithine could potentially improve interpersonal social-stress-associated fatigue without involving the HPA axis. Trial registration: UMIN Clinical Trials Registry: UMIN000048949.