Effects of mouth cleansing on the levels of exhaled nitrous oxide in young and older adults

Nitrous oxide (N2O) is produced by denitrification, i.e. by microbial reduction of nitrate (NO3−). Our previous studies have established an analytical method for demonstrating the existence of N2O in exhaled air, and we showed that levels of N2O in exhaled air increase with age after puberty. However, the source of this change and its biological significance are still unclear. The purpose of this study was to examine whether the oral microorganisms are the main source of N2O. We measured exhaled N2O in 35 young adults (aged 19–29 years) and 34 older adults (aged 61–79 years) before and after mouth cleansing. N2O was measured using an infrared-photoacoustic analyzer equipped with an optical filter (UA0985, 2215 cm−1). Participants were classified as producers and non-producers according to the levels of exhaled N2O relative to the level in the atmosphere. N2O production differed significantly between the young adult producers and the older adult producers. Mouth cleansing resulted in an immediate reduction in exhaled N2O in both groups. We only found seven (20.0%) producers in the young, and 32 (94.1%) producers in the older after mouth washing. The differences before and after mouth cleansing were significant in both groups (P<0.01 in the young and P<0.05 in the older). The oral cavity is a major source of N2O. However, since approximately half-levels of N2O were still observed in exhaled air after mouth cleansing, there may exist another N2O source in the human body.