A large number of negative air ions have been detected in forests, at spas, and near waterfalls. The air ion had been reported to improve the feelings of comfort, feelings of fatigue and occupational efficiency. Almost all the studies were reported by the short-term exposure of the air ions (2-5 hours) on human. We analyzed the physiological effects and laboratory findings of the long-term exposure of negative air ion (ca. 5000/cc, 5 hours/day, 3 weeks) in double-blind methods.
For this study, we made the negative air ion producing machines, in which the steam was combined with electric discharge by high-voltage electrodes. The machines could constantly produce high amount of negative ions (ca. 5, 000 counts/cc). We set these machines in the rest rooms of ten volunteer and programmed to spout negative air ions when they were sleeping at midnight (AM1:00-6:00) for 3 weeks. After 3 weeks exposure of negative air ions or sham condition, we checked the physical and mental tests and sampled the blood.
In the exposure of negative air ions, some of the depressive scales and subjective feelings (scores from Arthritis Impact Measurement Scales (AIMS2)) were better than in those in the sham condition, and the local perspiration of palm, which reflected sympathetic nerve function, also decreased by mental and physical stress in the exposure ions more than in the sham condition. This showed that the negative air ion decreased the stress of the sympathetic nerve function. In laboratory findings, there were no significant differences between the clinical data with ions and without ions, and it was shown that ion was harmless in the range of 5, 000 counts/cc 5 hours/day. The percentage of natural killer (NK) cells with the exposure of the ions was lower than without ions. This also indicated the air ion decreased the stress of human.
It was shown that the negative air ion might improve human activities and remove the stress. The mechanism of the negative air ions for human is not clear, so that further studies will be needed.