Effects of Mastication on the Autonomic Nervous System： An Examination of Gum Chewing in the Young Females

Abstract

The purpose of this study is to investigate the effect of mastication on the autonomic nervous system. The experimental subjects were 20 healthy young females. They were tested while doing three physical activities. Three physical activities were gum chewing alone, exercise alone, and gum chewing after exercise. During each activity the heart rate variability was measured together with heart rate（HR）, blood pressure（BP）on three occasions, by using an acceleration plethysmography system. The three occasions were before, immediately after, and 15minutes later. The heart rate variability was analyzed using frequency analysis to know the autonomic nerve balance, which is the activity valance（index: LF／HF） of the sympathetic nerve（index: LF）and parasympathetic nerve（index: HF）. The changes in HR, BP and LF／HF were examined using two- way repeated ANOVA to learn the influence of the three different activities over the course of time. Factors related to the changes in the LF／HF coursed by chewing were examined. As for the LF／HF, three different patterns over the course of time were observed depending on the activity being performed. During gum chewing activity, the LF／HF had a tendency to rise immediately after chewing compared to before, and then recover to the baseline. During exercise activity, the LF／HF was continuously elevated, and reached a significantly high level 15 minutes later. During activity of gum chewing after exercise, the LF／HF was highly elevated, but significantly decreased 15 minutes later compared to immediately after. This decrease in the LF／HF was mainly due to the elevation of HF. Factors related to the elevation of the LF／HF after gum chewing were the small elevation of HR, and the shortness of the period of exercise. There is a possibility that mastication moderately stimulates the sympathetic nerve, but when mastication is done in a condition of excitement coursed by exercise, it suppresses the excitability of the sympathetic nerve.