A study that collected more than 13 million hours of data from light sensors worn by 89,000 people has found that 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 per cent increased risk of death, whilst those exposed to high levels of daylight had a 17–34 per cent 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 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.”
Co-senior author, Associate Professor Andrew Phillips 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 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.
“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,” adds Associate-Professor Phillips.
Lead author, Dr 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 Dr 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.”
