JMIR Publications

ABSTRACT

Background:

Poor sleep quality can increase stress and lower well-being. Notably, Japanese people tend to be sleep-deprived and workers have high levels of stress. However, research evaluating the relationship between objective sleep assessments and stress and well-being in Japanese workers is lacking.

Objective:

The aim of this study was to explore the association between physiological data, such as sleep time and HRV, measured objectively by wearable devices, each of the three states: sleepiness, mood, and energy measured by EMA and use of rating scales for stress/well-being.

Methods:

A total of 40 office workers (%female, 50%; mean age, 40.4 years; SD, 11.8 years) participated in the study. Participants were asked to wear a wearable wristband device for 8 consecutive weeks. EMA on sleepiness, mood, and energy was conducted through email messages sent by the participants four times a day, each three hours apart, on eight designated days during the 8-week period. Their stress levels and perception of well-being were assessed using respective self-rating questionnaires. Participants were divided into quartiles based on the stress/wellbeing scores, and the sleep and heart-rate variability indices measured by the Fitbit were compared between the groups. The Mann-Whitney U test was used to compare the differences between the groups. Moreover, EMA results and the sleep and heart-rate variability indices were evaluated by a multilevel analysis.

Results:

The total response rate for the EMA was 87.3%, and the total Fitbit wear rate was 88.0%. When grouping by wellbeing and stress-related scores by quartiles and examining the differences between the groups, the group with the lowest stress or highest subjective satisfaction went to bed earlier (P < .001; P =0.01 respectively), while the group with highest stress had a greater variation in midpoint of sleep (P < .001). Based on multilevel analysis, the following relationships were found; analysis of intra-individual variability revealed that the energy was higher when the deviation of heart rate during sleep was lower on the previous day (β = -0.12, P < .001), and sleepiness was lower on the next day on days when sleep was longer (β = -0.10, P < .001). Analysis of inter-individual variability showed that participants with earlier midpoint of sleep have relatively higher energy (β = -0.26, P = .037).

Conclusions:

Greater sleep variabilities, that is, unstable bedtime and/or midpoint of sleep, were associated with higher levels of stress and lower levels of well-being. Better sleep indices, such as a lower heart rate during sleep and earlier average bedtime, were associated with higher daytime energy. Future research with a larger sample size utilizing these methods, focused on specific targets such as social jet lag, can provide further useful insights. Clinical Trial: UMIN-CTR UMIN000046858 https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000053392