Imbalance of nonparametric rest-activity rhythm and the evening-type of chronotype according to frailty indicators in elderly community dwellers

Background: Sleep health-related issues, such as poor subjective sleep quality during the night and nocturnal wakefulness, have been a focus of recent research on frailty. However, current trends regarding the chronotypes of older individuals with frailty have not been well documented, and information on the impact of frailty on circadian rest-activity patterns is limited. The aim of this research was to clarify the relationship among frailty, nonparametric rest-activity patterns, and chronotype in older community-dwelling subjects. Method: A survey was conducted between June and December 2018, and the participants of this study were recruited from among community-dwellers aged 60 years or older living in Akita prefecture, Japan. The frailty phenotype defined by the National Center for Geriatrics and Gerontology Study of Geriatric Syndromes (NCGG-SGS) was used to evaluate the frailty status of each participant. To evaluate nonparametric rest-activity rhythm (RAR) parameters (e.g., interdaily stability [IS], intradaily variability [IV], and relative amplitude [RA]), each participant wore an Actiwatch Spectrum Plus device on his or her non-dominant wrist for seven continuous days without removal. The Munich chronotype questionnaire-Japanese version (MCTQ-J) was also used to measure the midpoint of sleep in free days (MSF). Results: The final study cohort was composed of 105 participants (85.7% women) and was divided into 58 non-frail subjects, 45 pre-frail subjects, and 2 frail subjects. According to a binomial logistic regression analysis, the pre-frail individuals had a weaker grip strength (coefficient [beta], -0.18; odds ratio, 0.84; 95% confidence interval [CI], 0.76-0.93; p = .001) and a lower RA (beta, -8.78; odds ratio, 0.0002; 95% CI, 0.00-0.15; p = .01). In addition, correlation analyses also showed that the MSF was negatively associated with the RA in the pre-frail group (r = -0.30, p < .05) and positively correlated with the RA in the non-frail group (r = 0.26, p < .05); furthermore, the MSF of the pre-frail group occurred at a later time than that of the non-frail one (p = .03). Conclusion: The present study provides grounds for our proposal that pre-frailty is significantly associated with a low grip power and relative imbalance between rest and active statuses as indexed using nonparametric RAR parameters. Furthermore, elderly individuals with pre-frailty or frailty may have a later MSF time. However, these potential findings need to be validated in future research.