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Methods
Participants who accepted the invitation received a wrist-worn AX3 triaxial accelerometer (Axivity) with in-built light sensor (APDS9007 silicon photodiode sensor; spectral sensitivity λ = 470–650 nm) and were asked to wear the device on their dominant wrist for seven days under free-living conditions.
Participants were given a wrist wearable device that recorded their movement and light levels. They were requested to wear it on their dominant wrist for seven days while maintaining their daily routines. The light sensor in the device detects light between 470 and 650 nm.
Introduction
Healthy circadian rhythms are essential for mental health and well-being. Many psychiatric disorders are characterized by disrupted circadian rhythms and sleep.
Stable circadian rhythms play an important role in supporting human mental health. Many mental illnesses involve disturbances in circadian rhythms and sleep.
Results
In fully adjusted regression models (Model 3, adjusted for age, sex, ethnicity, photoperiod, employment, and physical activity; Fig. 2 and Table 2), higher night-time light exposure was associated with higher odds of major depressive disorder (MDD) (χ2 P < 5 × 10−16; fourth quartile odds ratio (ORQ4) = 1.30, 95% CI = 1.23–1.38), self-harm (χ2 P = 1.52 × 10−6; ORQ4 = 1.27, 95% CI = 1.14–1.42), generalized anxiety disorder (GAD) (χ2 P = 0.0001; ORQ4 = 1.23, 95% CI = 1.11–1.36), post-traumatic stress disorder (PTSD) (χ2 P = 2.23 × 10−10; ORQ4 = 1.34, 95% CI = 1.22–1.48), and psychosis (χ2 P = 0.0009; ORQ4 = 1.21, 95% CI = 1.09–1.34). There was no overall association with bipolardisorder (χ2 P = 0.18);
The fully adjusted statistical model showed that participants who were exposed to higher levels of light at night-time had greater odds of major depressive disorder (MDD), self-harm behaviour, generalized anxiety disorder (GAD), PTSD, and psychosis. By contrast, bipolar disorder did not show an overall association.
Discussion
Taken together, our findings are consistent with bright daytime light and low night-time light strengthening circadian rhythms as an antecedent to more robust mental health. Patterns of bright daytime light and low night-time light serve to enhance the amplitude and stability of the circadian clock as well as align its timing appropriately with daily activities.
In general, our findings suggest that more daytime light and less night-time light can regulate circadian rhythms, which may contribute to improved mental health. Bright daytime light and dim night-time light increase the strength and stability of human circadian clock while aligning its pace with daily activities.
Future Directions
Instead of relying on wrist-worn devices, future research could use more precise light measurement techniques to capture light exposure. With better measurements, researchers would be able to better understand how light influences the human circadian system and overall mental health.
Difficult Material
The most difficult part for me was understanding the statistical terms, such as incidence rate ratio (IRRQ4). Although I could grasp the general implications from the context, fully understanding these statistical measures would help me interpret the results more accurately.