More Nighttime Light Linked to Depression and Anxiety

Increased nighttime light exposure is linked to poor mental health outcomes, while increased daytime light has the opposite effect, finds a new study.

The link between light exposure and mental health has been quantified in a recent study by Monash School of Psychological Sciences and the Turner Institute for Brain and Mental Health in Melbourne, Australia. This extensive research, which involved data taken from almost 87,000 participants from the UK Biobank, found that excessive exposure to light during the nighttime is associated with an increased risk of psychiatric disorders, including anxiety and post-traumatic stress disorder (PTSD).

The study was led by Sean Cain, an associate professor at Monash University, and was published in Nature Mental Health.

The study also noted the potential benefits of increased daylight exposure. Participants exposed to higher levels of natural light during the day showed a 20% reduced risk of depression, while increased nighttime light exposure raised the depression risk by 30%. Similar associations were identified with cases of self-harm, psychosis, generalized anxiety disorder and PTSD.

“Our findings will have a potentially huge societal impact,” said Cain, who added that managing light exposure could potentially serve as a non-pharmacological approach to improving mental health. The impact of nighttime light exposure remained consistent, even when factors such as demographics, physical activity, season and employment were accounted for.

Modern living conditions, characterized by significant indoor living and artificial lighting, could be misaligning our biological systems, which function best with lots of daytime light and minimal light after dark, suggested Cain.

“Humans today challenge this biology, spending around 90 percent of the day indoors under electric lighting, which is too dim during the day and too bright at night compared to natural light and dark cycles. It is confusing our bodies and making us unwell,” he said.

Reference: Burns AC, Windred DP, Rutter MK, et al. Day and night light exposure are associated with psychiatric disorders: an objective light study in >85,000 people. Nat Mental Health. 2023:1-10. doi:10.1038/s44220-023-00135-8

This article is a rework of a press release issued by Monash University. Material has been edited for length and content.