Bright Nights and Dark Days Linked to Increased Mortality Risk

A comprehensive study analyzing over 13 million hours of data collected from light sensors worn by 89,000 individuals reveals a troubling connection between light exposure patterns and mortality risk. The research, published in the *Proceedings of the National Academy of Sciences*, indicates that exposure to bright nights and dark days can significantly affect health outcomes.

Researchers found that individuals exposed to high levels of light at night faced a 21-34% increased risk of death, while those who enjoyed bright daylight saw a 17-34% reduction in their mortality risk. Senior author and sleep expert Professor Sean Cain from Flinders University emphasizes, "Exposure to brighter nights and darker days can disrupt our circadian rhythms, which are linked to various health issues, including diabetes, obesity, cardiovascular disease, and increased mortality."

Co-senior author Associate Professor Andrew Phillips elaborates on the impact of light exposure on circadian rhythms. He notes that nighttime light can shift the timing and weaken the signals of the body’s central circadian pacemaker, which regulates various biological processes. "Disruption of circadian rhythms is associated with the development of metabolic syndrome, diabetes, and obesity, and is also implicated in cardiometabolic diseases like myocardial infarction and stroke," he explains.

The study analyzed data from 89,000 UK Biobank participants aged between 40 and 69, using wrist-worn sensors to track personal light exposure over an average follow-up period of 8 years. Results revealed that a disrupted circadian rhythm correlates with higher mortality risk, confirmed through computer modeling techniques. The researchers accounted for variables such as age, sex, ethnicity, and lifestyle factors in their analysis.

Lead author Dr. Daniel Windred highlights the importance of maintaining a dark environment during late night and early morning hours, when the circadian pacemaker is most sensitive to light. He advises, "Seeking bright light during the day and minimizing night light exposure may lead to better health and longevity."

The implications of this research are particularly significant for vulnerable populations, such as those in intensive care or aged-care settings. The findings suggest that simple, accessible strategies like avoiding night light and maximizing daylight exposure could reduce disease burden, especially for cardiometabolic conditions, and potentially increase longevity.