A study from Flinders Health and Medical Research Institute (FHMRI) published in the journal Proceeding of the National Academy of Sciences (PNAS), involving over 13 million hours of data, collected from wearable light sensors worn by 89,000 participants found that exposure to bright nights and dark days is associated with an increased risk of death.
Investigating personal light patterns and risk of mortality
This work from FHMRI Sleep Health investigated whether personal day and night light and lighting patterns that can disrupt circadian rhythms could predict the risk of mortality. The researchers examined the relationship of the exposure with all-cause and cardiometabolic mortality risk in 89,000 people who were enrolled in the UK Biobank between 40 and 69 years old. Metrics were recorded with wrist-worn sensors (wearables) and mortality was obtained via the National Health Service across a follow-up period of around 8 years.
Sleeping patterns were estimated for motion data, and cardiometabolic mortality was defined as any cause of death corresponding to diseases of the circulatory system, or endocrine and metabolic diseases. According to the researchers, the results showed that a disrupted circadian rhythm predicted higher mortality risk, which the researchers were able to determine using computer modeling techniques.
The study findings also took into account age, sex, ethnicity, photoperiod, and sociodemographic and lifestyle factors to show that those exposed to high levels of light at night had a 21-34% increased risk of death, and those exposed to high levels of daylight had a 17-34% reduction in the risk of death.
Brighter nights and darker days are disruptive
“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,” said senior author and sleep expert Professor Sean Cain from Flinders University. “These new insights into the potential adverse impact of light have shown us just how important personal light exposure patterns are for your health.”
Light exposure at night is known to disrupt our circadian rhythms by shifting the time (phase-shift) and weakening the signal (amplitude suppression) of the central circadian rhythm pacemaker which orchestrates these rhythms throughout the entire body, explains the study’s co-senior author, Associate Professor Andrew Phillips.
Detrimental consequences
“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,” said Associate Professor Phillips.
“The observed relationships of night light exposure with mortality risk may be explained by night light disrupting circadian rhythms, leading to adverse cardiometabolic outcomes,” adds Phillips. “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.”
The study findings demonstrate the importance of maintaining a dark environment throughout late evening and early morning hours when the central pacemaker is the most sensitive, and that brightness during the day can help to enhance our circadian rhythm, explains the lead author, Dr. Daniel Windred.
“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. “Across the general population, avoiding night light and seeking day light may lead to reduction in disease burden, especially cardiometabolic diseases, and may increase longevity.”
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