Sleeping in total darkness may protect your cardiovascular health
A striking new study presented at the American Heart Association (AHA) Scientific Sessions 2025 suggests that sleeping in total darkness could play a crucial role in protecting your heart. The research found that artificial light at night (LAN) exposure may trigger stress-related brain activity that inflames arteries — a key risk factor for heart attack and stroke.
How ambient light affects heart health
Researchers followed 466 adults, average age 55, who had undergone PET/CT brain scans at Massachusetts General Hospital between 2005 and 2008. None of them had heart disease or cancer at the time, making their later cardiovascular outcomes especially notable. The team used satellite data from the Suomi National Polar‑orbiting Partnership to estimate ground-level night-time brightness in the participants’ neighborhoods, excluding natural sources like starlight and moonlight.
Over a 10-year follow-up, 17 percent of the participants developed major cardiovascular issues. Crucially, for every standard-deviation increase in LAN exposure, there was a 35 percent higher chance of a heart attack in the next five years, and a 22 percent higher risk over ten years.
The connection seemed stronger for those living in environments with higher social or environmental stressors, such as traffic noise or lower-income neighborhoods. In these settings, even moderately increased light levels may worsen stress responses in the brain, driving systemic inflammation.
The science: artificial light, inflammation, and the brain
According to the study authors, artificial light can activate stress‑related neural pathways. This, in turn, may stimulate inflammatory responses in the arteries — a key step toward atherosclerosis and cardiovascular disease. This aligns with prior research showing that higher light levels during sleep (for example, 100 lux indoors) impair deep sleep, raise heart rate, and reduce insulin sensitivity.
Melatonin plays a key role, experts note. In darkness, your body produces melatonin, which helps regulate sleep and lower blood pressure. But when light intrudes at night, this process is disrupted, blood pressure dips are delayed, and stress hormones like cortisol may spike later — all of which can harm cardiovascular health over time.
What this means for you
Sleep quality is more than just duration — how dark your room is matters. Even low levels of ambient light can contribute to worse heart health. Here are some practical steps to create a darker, heart-health–friendly sleep environment:
- Install blackout curtains or shades. If standard curtains don’t block out light, consider blackout options or even temporary solutions like aluminum foil.
- Seal light gaps. A door undercut can leak light; roll up a towel or rug to block it, or switch off nearby lights.
- Use a sleep mask. A well-fitting eye mask is simple but effective in blocking light directly on your eyes.
- Opt for motion‑sensing nightlights. Instead of always-on nightlights, use lights that only turn on when you move — reducing unnecessary LAN exposure.
The big picture: sleep, inflammation, and heart disease
This study adds to mounting evidence that light pollution in bedrooms may not just disturb sleep — it may drive systemic inflammation that contributes to cardiovascular disease. Previous meta-analyses and cohort studies have already linked indoor LAN to sleep problems, metabolic disruption, and atherosclerosis.
Cardiologists emphasize that darkness during sleep helps initiate the body’s natural restorative processes — lowering blood pressure, calming stress systems, and regulating hormones. Over time, the cumulative benefit may help reduce the risk of heart disease, stroke, and other inflammation-driven conditions.
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