New research suggests that a common nighttime habit, one that many people engage in, could increase the risk of heart disease by up to 35 percent. The habit in question is exposure to artificial light at night, such as from a television, phone, or tablet.
Scientists presented their findings at the American Heart Association’s 2025 Scientific Sessions. The study analyzed brain scans and medical records from more than 450 adults who did not have existing heart disease. Using PET/CT imaging, the researchers observed stress activity in the brain and inflammation in the arteries. These two biological markers often appear years before cardiovascular disease develops.
The researchers then mapped the amount of artificial light each participant was exposed to at night, based on their home address. The results showed that people exposed to higher levels of artificial light at night had increased stress-related brain activity. This was particularly true in regions that activate the body’s “fight-or-flight” response. This brain activity was linked to greater inflammation in the arteries, a key early driver of heart disease. Over time, these biological signals translated into a higher risk of cardiovascular events.
The brain appears to interpret nighttime light as a form of stress. This triggers a chain reaction that can strain the heart over time. The study adds to a growing body of evidence that light exposure at night does more than just disrupt sleep. It may directly affect how the heart and brain function.
Most people know that light affects melatonin, the hormone that tells the body it is time to sleep. But melatonin is only part of the story. When the brain perceives light at night, it activates the sympathetic nervous system. This part of the body keeps a person alert and ready to respond to stress. That response is useful in a real threat, but less ideal when trying to rest. Over time, chronic activation of this “fight-or-flight” response can lead to inflammation, elevated blood pressure, and stiffer arteries. All of these increase cardiovascular risk.
Experts recommend making the bedroom a dark zone. Blackout curtains or a simple eye mask can block streetlight glow or the flicker from passing cars. Even dim light can disrupt the body’s nightly repair processes. Switching to warm, amber-toned lighting in the evening is also advised. Bright, blue-white LEDs are better for daytime when alertness is desired. Giving devices a curfew is another step. Phones, tablets, and TVs emit blue light that keeps the brain in daytime mode. Setting a “digital sunset” an hour before bed can help the body wind down naturally.
These small changes may seem simple, but light exposure is one of the few environmental stressors people can directly control. The research underscores that protecting the heart might start with something as simple as turning off the lights.
