Our world is getting brighter all the time. International Space Station astronaut Don Pettit recently posted a series of photos on X (formerly Twitter) documenting how our artificial light environment has changed over the past two decades. Gone are the warm, orange-yellow sodium streetlights, with bluish-white LEDs taking their place. It’s a dramatic transformation—and one that cuts down on energy use—but it’s also a shift toward a wavelength of light our biological clocks are more sensitive to.
Pettit’s photos also underscore that our planet is growing more luminous in general. Add to that our increasing reliance on blue-light-beaming devices and we’re getting a bigger dose of nighttime light than any generation of humans that came before us. And according to a new study published in the European Heart Journal, it could be affecting our cardiac health.
Read more: “The Birth of Light”
Light is the most important input to our circadian rhythms, and one of the systems our circadian clocks govern is the cardiovascular system. The relationship between the two, however, is still somewhat murky. “Previous observational studies have linked nighttime light exposure with a higher risk of cardiovascular disease, but little is known about the related cardiac structure and functional changes,” study author Lu Qi explained in a statement.
So Lu and his fellow public health epidemiologists from Tulane University strapped accelerometers with light meters to the wrists of more than 11,000 people enrolled in the United Kingdom’s BioBank study to measure their light exposure for a week. The team also took MRIs of their hearts and followed up with more cardiac MRIs three years later to find out whether things had changed.
They found structural changes in the hearts of people with nighttime light exposure of more than three lux—about the same amount received from the light of a full moon. In these individuals, the walls of the left ventricles had thickened, reducing the volume of the chamber responsible for pumping oxygen-rich blood out to the rest of the body. According to the team, roughly 24 to 49 percent of the structural changes could be explained by sleep duration being reduced to less than five or six hours.
“Ultimately, this study is more than an interesting observation,” the researchers wrote in an editorial on the findings. “It provides a crucial link between what satellites already show us, i.e. a planet glowing ever brighter at night, and the clinical reality unfolding inside our chests: hearts that are becoming stiffer, weaker, and less efficient.”
Of course, there are few caveats. The study only measured light exposure for a week, which might not be the best measure of habitual light exposure. Additionally, the recordings were made with a wrist-worn sensor, which means it could under- or overcount the amount of light received by the eyes. Finally, the average amount of thickening was measurable but slight (less than 3 percent), but could be enough to adversely affect those with existing cardiovascular issues.
What can you do to reduce your nighttime light?
Blackout curtains, warm bedroom lighting, and taping over any obnoxious standby LEDs on appliances can help. If you use an illuminated alarm clock, choose one that features a more circadian friendly wavelength, like red light. Finally, put your phone away before bed, preferably in another room.
We may not be able to stop the planet from getting brighter, but we hold the key to indoor light pollution in the palms of our hands. 
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Lead Image: Fehmiu Roffytavare / Shutterstock
