Deviation From Optimal Physical Activity Duration Worsens Depressive Symptoms Through High Sleep Reactivity and Poor Sleep Quality in Adult Volunteers From the Community

Physical inactivity is considered to increase depressive symptoms. There are also studies reporting that overly strenuous physical activity can negatively affect a person's mental state. Insomnia, which is associated with lower levels of physical activity and increased sleep reactivity, is also known to be associated with depression. However, the directionalities of the associations among these factors remain unclear. The aim of this study was to investigate whether both insufficient and excessive physical activity affect depressive symptoms through sleep reactivity and sleep quality. Between April 2017 and April 2018, self-administered surveys were provided to adult volunteers through our acquaintances at Tokyo Medical University. The study included 526 volunteers whose responses were considered valid. Demographic information, results of the International Physical Activity Questionnaire, the Ford Insomnia Response to Stress Test (FIRST), the Pittsburgh Sleep Quality Index, and the Patient Health Questionnaire-9 (PHQ-9) were used for analysis. Quadratic regression was performed to examine whether the PHQ-9 score was significantly explained by physical activity duration in a U-shaped curve. Path analysis was performed to identify indirect effects. Quadratic regression indicated the presence of an optimal physical activity duration (25.7 h/week) that was related to the lowest PHQ-9 score, and both insufficient and excessive physical activity could be expressed as a Difference from Optimal Physical Activity Duration (DOP). Path analysis demonstrated that DOP increased the PHQ-9 score through the FIRST score.These findings indicate that deviation from the optimal physical activity duration worsens depressive symptoms through high sleep reactivity.