For much of human history, nighttime was characterized by profound darkness, free from the intrusion of artificial lighting. Today, however, total darkness is increasingly uncommon. Recent studies have associated exposure to light during sleep with elevated rates of hypertension, obesity, and diabetes. Additionally, research published last year linked nighttime light to a higher incidence of heart failure and other cardiovascular issues over a decade.
Now, a new study published in the European Heart Journal on September 9 provides further evidence connecting evening illumination to cardiac health. The findings indicate that individuals who sleep with lights on exhibit structural changes in their hearts compared to those who sleep in darkness, suggesting the organ is working harder than normal.
The research utilized data from the UK Biobank, a massive database containing health and lifestyle information for approximately 500,000 participants. A subset of these individuals wore fitness monitors equipped with light sensors for one week, allowing for objective measurements of light exposure. Dr. Lu Qi, an epidemiology professor at Tulane University and a co-author of the study, highlighted the significance of this method. “That’s very unique, because most previous studies have used self-reported light exposure,” Qi noted.
Following the monitoring period, participants underwent cardiac MRIs before any diagnosable heart conditions emerged. Researchers divided the subjects into two groups: those with minimal nighttime light exposure and those routinely exposed to at least 3 lux of light—a brightness roughly equivalent to three candles held three feet away. Analysis of the MRI scans revealed that the hearts of those exposed to nighttime light had thicker walls and were less efficient at pumping blood.
Qi emphasized that while these structural changes do not constitute heart disease in themselves, they are precursors to its development. Angus Burns, an instructor in medicine at Harvard Medical School who co-authored related research last year, praised the study for adding detail to existing literature. He noted that while previous work established correlations between light at night and events like stroke and myocardial infarction, the use of heart MRI scans was a significant advancement.
The study is correlational, meaning it cannot definitively rule out the influence of other unidentified factors. Nevertheless, the data suggests that nighttime light may be a driving force behind metabolic and cardiovascular problems. The source of the illumination—whether hallway lights, electronic screens, or televisions—was not specified in the data.
Despite these nuances, experts recommend adhering to established sleep hygiene practices to mitigate risks. Participants were advised to make their sleeping environments as dark as possible, utilizing blackout curtains, turning off hall lights, and wearing eye masks. These measures, long recommended for better sleep, may also offer protective benefits for heart health.
Correlation isn’t causation, though. Maybe people with existing heart issues keep lights on to navigate at night? Worth considering.
Finally, objective data rather than just self-reports. This makes a compelling case for blackout curtains in every bedroom.