Sleep improvement by Kagawa Hinoki root volatiles in middle-aged women: a home-based pilot study

Middle-aged women face various stressors ranging from work-related to personal problems that brings out the sleep disturbance. In this study, we proposed essential oil prepared from the roots of Hinoki trees ( Chamaecyparis obtusa ) cultivated in Kagawa Prefecture as an alternative solution to sleep disturbance and proposed a home experiment to obtain realistic information compared with experiments in a laboratory environment. A single-blind cross over experiment has been conducted for 2 weeks with 12 women aged between 35 and 60 years (46 ± 6.72, mean ± SD) in each condition under Kagawa Hinoki’s root essential oil (KHREO) comparing with no scent situation (squalane oil) as a control. Physiological activity was measured by electroencephalography (EEG), and smartwatch, while psychological information was measured by the OSA sleep inventory MA. Volatile organic compounds in essential oils were analyzed using solid-phase microextraction–gas chromatography–mass spectrometry (SPME–GC–MS). This study revealed that the most abundant volatile compounds emitted from the essential oil were α-pinene, δ-cadinene, γ-cadinene, limonene, and α-muurolene. Results under visual analogue scale (VAS) show that KHREO was rated higher than the control condition in the categories of "scent strength", "scent liking", "bitterness", "relaxation", "comfort," "elegance", "nostalgia" and "woody scent". OSA sleep inventory MA also showed that participants under KHREO condition had better sleep quality especially in factor 1 (sleepiness at awakening) and factor 4 (fatigue recovery) after 13th day exposure. The EEG signal also showed increased slow-wave activity under KHREO which indicates the inducement of deep sleep from 7th day exposure. After using KHREO for 13 days, it was found that the frequency of awakenings during sleep, as detected by a smartwatch, decreased. This concluded that KHREO may play an important role in improving sleep quality by inducing deep sleep, reducing alertness during sleep and improvement from fatigue especially after 2 weeks of use.