Artificial light pollution at night (ALAN) has yet again been associated with another aspect of our health — mental illness. Studies such as this have investigated the impact of outdoor light at night and its association with the emergence of depressive symptoms in the Netherlands. Analysed data revealed a positive association between the exposure to outdoor ALAN within the immediate residential environment and depressive symptoms. Other studies conducted on Japanese elderly also suggested associations between bed-room measured light level and depressive symptoms (Obayashi et al., 2018). Be it indoors or outdoors, we can’t seem to escape artificial light and the harms it can bring to our mental health. 

 

How Light leads to Depressive Symptoms

The most common explanation to the effects of light on mood disorders is explained by a disruption of circadian rhythmicity (Lyall et al., 2018). And this disruption of circadian rhythmic systems which affects mood can be explained through the indirect effect of light on our sleep system, neurotransmission, hormone secretion and gene expression (Dearmont, n.d.). 

Sleep disruptions

Firstly, our circadian rhythm serves to synchronize and regulate some behavioural and biological processes of our body through cycles, such as our sleep-wake behaviour. Disruptions to our sleep-wake behaviour and the failure to complete a full circadian cycle, lowers the quality and quantity of sleep and contributes to the further suppression of our circadian systems which results in mood disorders. 

Disruption to Neurotransmitters 

Light has also been attributed to the disruption of expressions of neurotransmitters such as monoamine, which have in turn, been attributed to depressive symptoms. Furthermore, the treatment of depression usually targets neurotransmitters like serotonin, dopamine and norepinephrine which makes up monoamine, further supporting this association between light and mood disorders. 

Gene Expression

Lastly, intrinsically photoreceptive retinal ganglion cells, a type of photoreceptor in our retinas, have also been found to express melanopsin which makes the cells highly photosensitive. In addition, melanopsin is found to have a high responsiveness to blue light which promotes our circadian rhythms to synchronize with a 24 hour light day. This becomes particularly problematic when we consider speculations made that suggest artificial light-induced disruptions in the day-lengths has an effect on people’s mood (LeGates et al., 2012). 

 

Why It Matters

If light pollution indeed leads to mood disorders, it will prove to be a significant problem. With the growing evidence on the association between disrupted circadian rhythms and mood disorders, we ought to pay more attention to light, which is commonly believed to be the strongest influencing factor of circadian rhythms. Furthermore, the very blue light which dominates our LED-lit streets has been recorded to evoke the strongest response to our circadian rhythms as it can suppress the production of melatonin (Haim and Zubidat, 2015), which is highly influential over sleep-wake-cycles. 

Additionally, the association with mental illness is a particularly problematic association. Mental illness has the potential to reduce up to 13% of disability-adjusted life-years (Vigo et al., 2016). Hence, evidence that points to associations between the exposure to artificial light at night and the development of mental illness should be of our concern. 

In response to this, we can make several changes. First, we can prevent the disruption of our circadian rhythms by changing our lightbulb to warmer hues which reduce our exposure to blue light at night. Alternatively, we can also attempt to reset our circadian rhythm by going outside during the day. Exposure to sunlight signals our body that it is daytime end serves as a natural regulating system to our circadian rhythm. Let’s take these little steps within our own capacity to protect our minds and health!

 

Till next time!

Trudie

References:

• Dearmont, C. (n.d.). How blue light affects mental health. Mental Health America. https://www.mhanational.org/blog/how-blue-light-affects-mental-health
• Haim, A., & Zubidat, A. E. (2015). Artificial light at night: Melatonin as a mediator between the environment and epigenome. Philosophical Transactions of the Royal Society B: Biological Sciences, 370(1667), 20140121. https://doi.org/10.1098/rstb.2014.0121
• Helbich, M., Browning, M. H., & Huss, A. (2020). Outdoor light at night, air pollution and depressive symptoms: A cross-sectional study in The Netherlands. Science of The Total Environment, 744, 140914. https://doi.org/10.1016/j.scitotenv.2020.140914
• LeGates, T. A., Altimus, C. M., Wang, H., Lee, H., Yang, S., Zhao, H., Kirkwood, A., Weber, E. T., & Hattar, S. (2012). Aberrant light directly impairs mood and learning through melanopsin-expressing neurons. Nature, 491(7425), 594-598. https://doi.org/10.1038/nature11673
• Lyall, L. M., Wyse, C. A., Graham, N., Ferguson, A., Lyall, D. M., Cullen, B., Celis Morales, C. A., Biello, S. M., Mackay, D., Ward, J., Strawbridge, R. J., Gill, J. M., Bailey, M. E., Pell, J. P., & Smith, D. J. (2018). Association of disrupted circadian rhythmicity with mood disorders, subjective wellbeing, and cognitive function: A cross-sectional study of 91 105 participants from the UK Biobank. The Lancet Psychiatry, 5(6), 507-514. https://doi.org/10.1016/s2215-0366(18)30139-1
• Obayashi, K., Saeki, K., & Kurumatani, N. (2017). Bedroom light exposure at night and the incidence of depressive symptoms: A longitudinal study of the HEIJO-KYO cohort. American Journal of Epidemiology, 187(3), 427-434. https://doi.org/10.1093/aje/kwx290
• Vigo, D., Thornicroft, G., & Atun, R. (2016). Estimating the true global burden of mental illness. The Lancet Psychiatry, 3(2), 171-178. https://doi.org/10.1016/s2215-0366(15)00505-2