Summary: A large-scale study analyzing over 13 million hours of light exposure data from 89,000 people has found that exposure to high levels of night light and limited daylight disrupts circadian rhythms, increasing mortality risk. The study, published in Proceedings of the National Academy of Sciences, underscores the importance of day and night light patterns in health.
Key Takeaways:
- Night Light Exposure Raises Mortality Risk: The study found a 21–34% increased risk of death among those exposed to high night light levels, linking circadian rhythm disruption to adverse health outcomes.
- Daylight Reduces Mortality Risk: Individuals with high daytime light exposure had a 17–34% reduced risk of death, suggesting daylight’s role in supporting optimal circadian function.
- Circadian Rhythm Disruption Impacts Health: Disrupted circadian rhythms were associated with higher mortality risk, especially from cardiometabolic diseases, emphasizing the health effects of maintaining a natural day-night light cycle.
A study of more than 13 million hours of data, collected from light sensors worn by 89,000 people, has found exposure to bright nights and dark days is associated with an increased risk of death.
Researchers investigated whether personal day and night light, and lighting patterns that disrupt our circadian rhythms, predicted mortality risk.
Published in the journal Proceedings of the National Academy of Sciences, the results show that those who were exposed to high levels of light at night had a 21–34% increased risk of death, while those exposed to high levels of daylight had a 17–34% reduction in their risk of death.
“Exposure to brighter nights and darker days can disrupt our circadian rhythms, a disruption that is known to lead to various health issues including diabetes, obesity, cardiovascular disease, mental health issues and increase the risk of death,” says senior author and sleep expert professor Sean Cain, PhD, from Flinders University, in a news release. “These new insights into the potential adverse impact of light have shown us just how important personal light exposure patterns are for your health.”
Night Light Disrupts Circadian Rhythms
Co-senior author, associate professor Andrew Phillips, PhD, says that light exposure at night disrupts circadian rhythms by shifting the timing (phase-shift) and weakening the signal (amplitude suppression) of the central circadian ‘pacemaker’ which orchestrates circadian rhythms throughout the body.
“Disruption to the body’s circadian rhythms is linked to the development of metabolic syndrome, diabetes, and obesity and is also strongly implicated in the development of cardiometabolic diseases including myocardial infarction, stroke, and hypertension,” says Phillips in a news release. “The observed relationships of night light exposure with mortality risk may be explained by night light disrupting circadian rhythms, leading to adverse cardiometabolic outcomes.
Phillips adds, “Our findings clearly show that avoiding night light and seeking daylight may promote optimal health and longevity, and this recommendation is easy, accessible, and cost-effective.”
Relationships Between Light and Health
The study authors, from FHMRI Sleep Health, examined the relationship of personal light exposure with all-cause and cardiometabolic mortality risk in 89,000 UK Biobank participants, who were between 40 and 69 years old. Metrics were recorded with wrist-worn sensors and participant mortality was captured by the National Health Service across a follow-up period of approximately eight years.
Sleep duration, sleep efficiency, and midsleep were estimated from motion data, while cardiometabolic mortality was defined as any cause of death corresponding to diseases of the circulatory system, or endocrine and metabolic diseases.
The research also showed a disrupted circadian rhythm predicted higher mortality risk, which the authors were able to determine using computer modelling. Findings accounted for age, sex, ethnicity, photoperiod, and sociodemographic and lifestyle factors.
Importance of Light Timing
Lead author Daniel Windred says that the findings demonstrate the importance of maintaining a dark environment across the late night and early morning hours, when the central circadian “pacemaker” is most sensitive to light, and seeking bright light during the day to enhance our circadian rhythms.
“Protection of lighting environments may be especially important in those at risk for both circadian disruption and mortality, such as in intensive care or aged-care settings,” says Windred in a news release. “Across the general population, avoiding night light and seeking daylight may lead to reduction in disease burden, especially cardiometabolic diseases, and may increase longevity.”
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