The Beneficial Effects of Coffee on Stress and Fatigue can be Enhanced by the Addition of GABA ―A Randomized, Double‒blind, Placebo Controlled, Crossover‒designed Study―

Background It is known that oral γ-aminobutyric acid（GABA）administration shows stress-reducing, fatigue-relieving, and relaxation-inducing effect on humans. As coffee is often drunk in expectation of relax, coffee added with GABA can be an effective functional food. In case of the commercial products containing GABA, the effect of GABA is not always displayed because of the influence of other components in the products. Based on these backgrounds, we aimed to investigate the effects of GABA added in coffee on stress and fatigue.Methods A randomized, double-blind, placebo controlled, crossover-designed study was conducted. Nineteen subjects took coffee and coffee added with 28 mg of GABA as test samples and carried out 17 min-arithmetic task to induce stress and fatigue. Salivary chromogranin A（CgA） was measured for evaluation of subjectsʼ stress before and after arithmetic task. A self-diagnostic questionnaire using visual analogue scale（VAS）was used for self-evaluation of subjectsʼ fatigue. Prior to this study, a study for baseline measurement in which subjects took water as a test sample was conducted. Results CgA in coffee added with GABA group reduced to 75％ of initial value after 30 min and it was significantly lower than that in coffee group（P＜0.01）and water group（P＜0.01）.Although CgA in coffee group increased to 107％ of initial value after 30 min, it was significantly lower than that in water group（P＜0.05）. VAS questionnaire showed that coffee added with GABA significantly suppressed the accumulation of fatigue 60 min after compared to coffee group（P＜0.05）and water groups（P＜0.05）. Conclusion GABA exhibited its stress-reducing and fatigue-relieving effect even in coffee. Coffee itself also showed stress-reducing effect, and the effects of coffee was enhanced by the addition of GABA.