Effect of Japanese dashi on Autonomic Nervous System Activity and Mental Fatigue in Humans

Abstract

The Japanese soup stock known as dashi is used in many traditional Japanese cuisines and its taste and flavor are assumed to be fundamental components of most dishes. Recently, some studies have indicated that long-term intake of dashi has certain health benefits. In this study, we focused on the immediate effect of dashi intake on autonomic nervous system (ANS) activity and mental fatigue. Twenty-four healthy, non-smoking volunteers participated. The subjects consumed an assigned breakfast at 09:00, and the experiments were conducted between 10:30 and 11:30. Heart rate variability (HRV) was used as an indicator of ANS activity. To measure the degree of mental fatigue, the flicker test was performed before and after a simple calculation task, the “Uchida Kraepelin Test” for 30 minutes. Subjective assessment of emotional state was also conducted using a Visual Analog Scale (VAS) . We observed a transient increase of parasympathetic nervous activity after intake of dashi. Olfactory perception of dashi odor also induced a similar effect on ANS. The flicker test and VAS evaluation demonstrated that dashi intake reduced the accumulation of fatigue caused by the calculation task. These results suggests that dashi may exert its relaxation and anti-fatigue effects through elevation of parasympathetic nervous activity, and that the aroma of dashi may have an important role in this function.