The purpose of this study was to clarify the effects of ingesting spa water on electrogastrography and heart rate variability in humans. The subjects were eight youths (average age 22.3 years old). We measured three and six circles per minute (cpm) power of electrogastrography (EGG), the high-frequency (HF: 0.15-0.4Hz) components, and the ratio of low-frequency (LF: 0.04-0.15Hz) components to HF components in heart rate variability (HRV) during 90 minutes. We also assessed the taste of water, pain or abnormalities in the stomach by questionnaire. The subjects ingested the spa water or purified water after thirty minutes, and ingested no water on a different day. The six cpm power of EGG, presumably reflecting instestinal activity, was significantly increased with spa water ingestion. The three cpm power of EGG, presumably reflecting stomach activity, did not change under any conditions. The HF components in HRV, presumably reflecting cardiac parasympathetic activity, tended to increase with ingestion of spa water. The ratio of LF to HF components in HRV, presumably reflecting cardiac sympathetic activity, significantly decreased with ingestion of spa and purified water. There was no difference in the answers of the questionnaire. These findings suggest that spa water ingestion activates instestinal activity, increasing parasympathetic nerve activity and suppressing sympathetic nerve activity in humans.
