A study published in 2023¹ reveals that the level of light exposure during the day and night can have an impact on self-harm, along with many psychiatric disorders. With data from over 86,500 individuals, it is the largest study to date analyzing the relationship between mental health and light exposure.

Many psychiatric disorders are characterized by disrupted sleep and circadian rhythms, our 24-hour internal clock regulated by light exposure. These rhythms are destabilized by modern industrialized societies and electric lighting.

The study found that brighter light at night was associated with greater risk for major depressive disorder, self-harm behaviors, PTSD, psychosis, general anxiety disorder, and poorer self-reported well-being. On the other hand, brighter light during the day was associated with lesser risk for major depressive disorder, self-harm, PTSD, psychosis, and had higher chances for better well-being. Interestingly, these associations were independent and additive, meaning that the effects of one didn’t cancel the effects of the other. For example, an individual exposed to brighter light both during the day and night had lesser risk for self-harm than someone with bright light during the night and none during the day, but still greater risk than someone exposed to brighter light during the day and none during the night. These results were also not impacted by demographic or physical activity.

The 25% people in the sample with the brightest night time light had about 30% more risk of self-harm.

However, it isn’t clear if imbalanced circadian rhythms are a cause of a consequence of psychiatric disorders. Yet, providing healthier light exposure could be a non-pharmacological treatment to improve mental health.

Reference

[1] Burns, A. C., Windred, D. P., Rutter, M. K., Olivier, P., Vetter, C., Saxena, R., Lane, J. M., Phillips, A. J. K., & Cain, S. W. (2023). Day and night light exposure are associated with psychiatric disorders: an objective light study in >85,000 people. Natural Mental Health. https://doi.org/10.1038/s44220-023-00135-8