A comprehensive study encompassing over 13 million hours of data gathered from light sensors worn by 89,000 participants has uncovered a significant correlation between exposure to bright nocturnal environments and dark daytime conditions and an elevated mortality risk. The research assessed whether individual exposure to varying light conditions and the resultant disruption of circadian rhythms could predict mortality risks.
The findings, published in the prestigious journal Proceedings of the National Academy of Sciences, indicate a stark contrast in mortality risks associated with different light exposures. Specifically, individuals subjected to high levels of light during nighttime exhibited a 21–34% increase in the risk of death. Conversely, those who experienced high levels of natural daylight demonstrated a 17–34% decrease in mortality risk.
The study highlights the profound impact of light-induced disruption on circadian rhythms — the internal process that regulates the sleep-wake cycle and other physiological processes.
According to Professor Sean Cain of Flinders University, a senior author of the study and an expert in sleep research, disruptions to these rhythms are known to precipitate a range of health issues, including diabetes, obesity, cardiovascular diseases, and mental health disorders, all of which contribute to an increased mortality risk.
Professor Cain further explained that the study’s insights into the detrimental effects of inappropriate light exposure underscore the critical importance of managing personal light exposure for health preservation. Echoing his sentiments, Co-senior author Associate Professor Andrew Phillips pointed out that nighttime light exposure disrupts the body’s circadian rhythms by altering the timing (phase shift) and diminishing the strength (amplitude suppression) of signals from the central circadian ‘pacemaker’, which coordinates these rhythms across different body systems.
Associate Professor Phillips elaborated on the connections between circadian rhythm disruptions and the onset of metabolic syndrome, diabetes, obesity, and various cardiometabolic diseases, such as myocardial infarction, stroke, and hypertension. He suggested that the observed correlation between nocturnal light exposure and mortality risk could largely be attributed to these disruptions, which lead to adverse cardiometabolic outcomes.
The study’s practical implications were emphasized by the researchers, who advocate for avoiding artificial light at night and pursuing natural daylight as simple, accessible, and cost-effective strategies to foster optimal health and longevity. These recommendations stem from their analysis of data from the UK Biobank, involving middle-aged participants monitored over approximately eight years. During this period, all-cause and cardiometabolic mortality data was meticulously collected and analyzed, factoring in variables such as age, sex, ethnicity, photoperiod, and socio-demographic and lifestyle factors.
Dr Daniel Windred, the study’s lead author, commented on the importance of maintaining dark conditions during the late night and early morning hours when the central circadian pacemaker is most receptive to light. He noted that exposure to bright light during daytime could significantly enhance circadian rhythm function. Dr Windred also stressed the potential benefits of protecting lighting environments, particularly in intensive care or aged-care facilities where individuals are more vulnerable to circadian disruptions and associated mortality risks.
In conclusion, the research offers compelling evidence that managing light exposure could drastically reduce the incidence of cardiometabolic diseases and enhance longevity across the general population. This groundbreaking study not only sheds light on the pivotal role of circadian rhythms in overall health but also provides actionable recommendations that could significantly reduce the burden of disease.
More information: Daniel Windred et al, Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in >88,000 individuals, Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2405924121
Journal information: Proceedings of the National Academy of Sciences Provided by Flinders University
