Nighttime exposure to light may raise cardiovascular risk by up to 50% - Harvard Gazette

"Angus Burns, a postdoctoral fellow at Harvard Medical School and Brigham and Women's Hospital, said the work highlights the potency of our circadian rhythm, which not only regulates sleep, but also independently affects nearly every organ in the body, changing how they function when we nod off. For those experiencing the brightest nights, the research showed increased risk of between 30 percent and 50 percent for heart attack, stroke, heart failure, atrial fibrillation, and coronary artery disease."

"Burns and colleagues almost missed the chance to conduct the study. Burns was intrigued when he learned of the UK Biobank database, which used biosensor-loaded wristwatches to track more than 100,000 participants, night and day, for a week. The resulting database is the largest known of physiological information related to participants' sleep and wake habits. But even though the schematics said the devices contained light sensors, the data downloaded from the watches didn't include exposure to nighttime light sources."

Exposure to light at night increases risk of heart attack, stroke, heart failure, atrial fibrillation, and coronary artery disease by approximately 30 to 50 percent for those experiencing the brightest nights. The effect operates through disruption of the master biological clock, the circadian rhythm, rather than through sleep loss alone. The circadian rhythm independently regulates nearly every organ and alters organ function during sleep. Data were derived from biosensor-equipped wristwatches in the UK Biobank tracking over 100,000 participants day and night for a week. Light exposure measurements required separate extraction from device data. Light exposure is presented as a novel, modifiable cardiovascular risk factor that could be added to prevention guidelines.

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