Brazil study links common habit to 35% higher heart risk

A new study 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. 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 markers that can appear years before cardiovascular disease develops. The team then mapped the amount of artificial light each participant was exposed to at night based on their home address.

The study found that people exposed to higher levels of artificial light at night showed increased stress-related brain activity, particularly 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, triggering a cascade that can strain the heart.

Light at night does more than suppress melatonin, the hormone that signals sleep. It activates the sympathetic nervous system, which keeps the body alert and ready to respond to stress. While this response is useful in real threats, chronic activation during rest can lead to inflammation, elevated blood pressure, and stiffer arteries. These changes increase cardiovascular risk over time.

To reduce the impact, experts recommend making the bedroom a dark zone using blackout curtains or an eye mask. Switching to warm, amber-toned lighting in the evening can help, as bright blue-white LEDs are better suited for daytime alertness. Setting a “digital sunset” an hour before bed by turning off phones, tablets, and TVs can allow the body to wind down naturally. Outdoor lights with motion sensors or timers can also reduce unnecessary brightness.

This research adds to decades of evidence connecting circadian disruption with chronic disease. Protecting heart health may start with simple changes like turning off lights at night. The study highlights that light exposure is one of the few environmental stressors people can directly control.