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.

High levels of negative ions have been detected in the air in forests, at spas, near waterfalls, and so forth, and there have been reported that they have a favorable effect on human beings' feeling of comfort and their feeling of fatigue. In this study we prepared an experimental room in which it was possible to maintain temperature constant at 25°C and constant humidity, and turn the supply of negative ions on and off, and in addition to assessing comfort level and fatigue level subjectively, we assessed them by means of the -wave component of the EEG, which indicates the degree of relaxation, and by auditory evoked potential P300, which reflects attentiveness and degree of fatigue.
Methods: The subjects were 15 healthy physicians and nurses. The experiment was conducted in a room maintained at a constant temperature of 25°C and a constant humidity of 50% during a 2-hour period on different days without informing the subjects of whether the air was loaded with negative ions or not. Constant temperature and humidity were maintained, and the level of negative ions was adjusted by using a shinki genertor (Geochto Ltd.). The parameters measured were determined with a flicker test and P300 (auditory evoked) test, and the α-wave ratio was calculated from the 60-minute closed-eye resting EEG.
Results: A higher percentage of subjects reported subjective comfort when the air was loaded with neagtive ions (6/15, 40%) than when it was not (4/15, 27%).
Significant difference was not observed in the P300 tests, but the α₂ (10-13Hz) ratio of the EEG and flicker test tended to be higher with negative ion-air than without nagative ion-air.

Effect of foot bath on sleeping time in 3 old patients (70, 82, 84 years old) was investigated. After 2-days control period, feet were immersed in a water bath containing about 1, 000ppm CO₂ at 40-41°C for 15 minutes at 17:00 for 3 consecutive days. Wrist Mini-motion-logger actigraph was used for recording their activities. The hour for lights-out was 21:00 and that of rising was 06:00. They went to bed between 20:30-20:50 and woke up at 05:30 next morning. In 2 patients, sleeping time at night began to increase on the second immersion day, which continued even on the following 2 days without foot bath. All the patients showed no changes in daytime activities. They were satisfied with foot bath and felt warmth not only in their feet but also in their bodies. No remarkable side effects were observed in the present study. Foot bath is thought to be effective to treat insomnia.

Objective: We studied immunological and physiological effect by the polarized infrared light irradiation near the neck stellate ganglion. Methods: Subjects were eleven healthy volunteers (age 21-22 years old, male). The polarized infrared light irradiation system (Super Lizer HA-550) for 20 minutes was used for the irradiation near the stellate ganglion. In the dummy, they were treated by the same irradiation instrument that the light were obstructed completely. We analyzed hematological test and perspiration quantity and temperatures of limbs and blood pressure before and after the irradiation. Results: The leukocytes decreased (p<0.01) and NK cells decreased after the irradiation significantly. The hormone and blood pressure did not significantly change. The perspiration of right hand (irradiated side) was significantly decreased. The peripheral temperature of bilateral upper and lower limbs elevated after the irradiation. Conclusion: It was considered that the effect by the polarized infrared light irradiation near the stellate ganglion was the same with the sympathetic nervous ganglion block which dilated arteries and increased of peripheral circulation, and inhibited the sympathetic nervous function.