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A groundbreaking study spanning over 13 million hours of light exposure data has revealed a significant link between irregular light exposure and increased mortality risk. Conducted by researchers at FHMRI Sleep Health and published in the Proceedings of the National Academy of Sciences, the study examined 89,000 UK Biobank participants, uncovering that bright nights and dim days may carry severe health consequences.
The study tracked light exposure through wrist-worn light sensors, recording the day-to-night light patterns of individuals aged 40 to 69 years old over an eight-year period. Findings indicated that people exposed to high levels of light at night experienced a 21-34% higher risk of mortality. Conversely, those exposed to adequate daylight saw a 17-34% decrease in mortality risk, highlighting the critical role of maintaining a natural day-night light cycle.
“Exposure to brighter nights and darker days disrupts our circadian rhythms, increasing susceptibility to a range of health issues like diabetes, obesity, cardiovascular disease, and mental health disorders, ultimately elevating the risk of death,” stated senior author Professor Sean Cain, a sleep expert from Flinders University.
The Body’s Clock and Health: How Light Impacts Circadian Rhythms
The body’s circadian rhythm, often referred to as its “biological clock,” governs essential processes like sleep, hormone release, and metabolism. Co-senior author Associate Professor Andrew Phillips explained that exposure to light at night disrupts this rhythm by altering the timing (phase-shift) and reducing the strength (amplitude suppression) of the central circadian “pacemaker.” This pacemaker coordinates circadian rhythms across the body, and disruptions can contribute to a variety of health conditions, including metabolic syndrome, cardiovascular disease, and hypertension.
“Disruption to the body’s circadian rhythms is linked to the development of metabolic syndrome, diabetes, and obesity, and is strongly implicated in the risk of cardiometabolic diseases such as myocardial infarction and stroke,” Associate Professor Phillips noted.
The research not only revealed a higher mortality risk associated with irregular light exposure but also suggested practical strategies for reducing this risk: avoiding night-time light and increasing daytime light exposure. “Our findings emphasize that maintaining dark environments during the late night and early morning hours, while seeking bright light during the day, can significantly bolster our health,” added Dr. Daniel Windred, lead author of the study.
Implications for Healthcare and Everyday Life
The implications of this study are particularly relevant for people in controlled lighting environments, such as patients in intensive care or elderly individuals in care facilities. For these vulnerable groups, special attention to lighting could mitigate circadian disruption and improve overall health outcomes.
The findings also underscore a simple, cost-effective intervention for the general population: embracing natural light during the day while minimizing exposure to artificial light at night. According to the researchers, these changes could alleviate disease burden, particularly for cardiometabolic diseases, and ultimately extend life expectancy.
This comprehensive study adjusted for factors including age, sex, ethnicity, and lifestyle, solidifying the association between light exposure and mortality. With the evidence suggesting clear health risks from disrupted circadian rhythms, Professor Cain remarked, “These new insights reinforce the critical importance of personal light exposure patterns for our health.”
In an age of pervasive artificial light, from smartphones to city streetlights, this study serves as a powerful reminder of the benefits of aligning with nature’s rhythms.
