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Exposure to Light at Night Messes with our Internal Body Clock




A new study has found that exposure to light at night messes with our internal body clock, increasing the risk of mental illness, while daytime light exposure reduces that risk. The findings offer a simple and effective, non-pharmacological means of improving mental health.


Our internal body clock, or circadian rhythm, regulates cycles of alertness and sleepiness by responding to the changes in light in our environment. While other cues such as exercise, social activity and temperature can affect circadian rhythm, light remains the most powerful influence.

It’s known that disturbances in circadian rhythm are a common feature of many psychiatric disorders. So, it makes sense that light exposure is a modifiable environmental risk factor in mental illness. To investigate, Monash University researchers led the world’s largest study on the effect of exposure to daytime and nighttime light on mental illness risk.

The researchers recruited 86,772 adult participants from the UK Biobank who were examined for their exposure to light, sleep, physical activity and mental health. They found that in those exposed to high amounts of light at night, the risk of depression increased by 30%, while in those exposed to high amounts of daytime light, their risk of depression fell by 20%.

Similar patterns were seen for self-harming behavior, psychosis, bipolar disorder, generalized anxiety disorder, and PTSD. The findings were consistent when accounting for demographic factors, physical activity, sleep, shift work, living environment and cardiometabolic health. “Our findings will have a potentially huge societal impact,” said Sean Cain, one of the study’s co-authors. “Once people understand that their light exposure patterns have a powerful influence on their mental health, they can take some simple steps to optimize their wellbeing. It’s about getting bright light in the day and darkness at night.” The researchers say that modern life – particularly artificial light and the light from devices like phones, computers and TV screens – has confused our internal body clocks, challenging how our brains have evolved to work best during the bright light of day.

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

The study’s findings demonstrate that avoiding light at night and seeking light during the day may be a simple and effective non-pharmacological way of improving mental health.


“Once people understand that their light exposure patterns have a powerful influence on their mental health, they can take some simple steps to optimize their wellbeing. It’s about getting bright light in the day and darkness at night.”



Our internal body clock, or circadian rhythm, regulates cycles of alertness and sleepiness by responding to the changes in light in our environment.



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elocal Digital Edition – November 2023 (#271)

elocal Digital Edition
November 2023 (#271)


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