New research presented at the American Heart Association’s 2025 Scientific Sessions suggests that exposure to artificial light at night may increase the risk of heart disease by up to 35 percent. The study found that nighttime light can affect stress levels, arteries, and long-term heart health, not just sleep quality.
Researchers analyzed brain scans and medical records from more than 450 adults without existing heart disease. Using PET/CT imaging, they observed brain stress activity and arterial inflammation, two biological markers that often appear years before cardiovascular disease develops. They also mapped how much artificial light each participant was exposed to at night based on their home address.
The findings showed that people exposed to higher levels of artificial light at night had increased stress-related brain activity, particularly in regions that activate the body’s fight-or-flight response. This brain activity correlated with greater inflammation in the arteries, a key early driver of heart disease. Over time, these biological signals translated into a significantly higher risk of cardiovascular events.
The brain appears to interpret nighttime light as a form of stress, kicking off a cascade that can quietly wear down the heart. Most people already 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 does more than suppress melatonin; it activates the sympathetic nervous system, the part of physiology that keeps a person alert and ready to respond to stress.
That response is useful when navigating a real threat, but less ideal when lying in bed 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 which increase cardiovascular risk.
To protect heart health and circadian rhythm, 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 and saving bright, blue-white LEDs for daytime when alertness is desired can also help.
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. For outdoor lighting, motion sensors or timers can reduce unnecessary brightness, which is better for health and energy bills.
Artificial light at night does not just interfere with sleep; it may quietly strain the cardiovascular system in ways that build up over time. This research adds to decades of evidence connecting circadian disruption with chronic disease, underscoring that protecting the heart might start with something as simple as turning off the lights.
