BY THE OPTIMIST DAILY EDITORIAL TEAM
A growing body of research suggests that a dark bedroom isn’t just nice for sleep. Getting your shut-eye in a pitch black room may actually be vital for long‑term heart health. A new study presented at the American Heart Association Scientific Sessions 2025 found that exposure to ambient light while sleeping was linked to increased stress in the brain, heightened arterial inflammation, and ultimately, a greater risk of heart attack and stroke.
Sleeping in bright environments stimulated stress-related brain activity that can inflame arteries throughout the body. Over a ten‑year follow‑up period, 17 percent of participants developed major cardiovascular issues. The pattern was clear: more artificial light at night meant greater cardiovascular risk. The researchers found that each standard deviation increase in nighttime light exposure came with a 35 percent higher chance of heart attack over five years, and a 22 percent higher risk over 10.
Those living in environments with added stressors, such as traffic noise or lower neighborhood income, were particularly vulnerable to the effects of light at night.
How the study worked
The research drew on PET/CT brain scans from 466 adults who visited Massachusetts General Hospital between 2005 and 2008. None of the participants had heart disease or cancer at the time. Their median age was fifty‑five, 43 percent were male, and nearly 90 percent were white.
To determine how much light participants were exposed to at night, the researchers used satellite data from NASA’s Visible Infrared Imaging Radiometer Suite. Advanced modeling helped estimate ground‑level sky brightness around each home.
While the findings are preliminary and not yet peer reviewed, sleep experts say they align with previous evidence. “Both animal and human intervention studies have demonstrated that LAN can disrupt multiple neurophysiological systems,” said Jonathan Cedernaes, PhD, a sleep scientist at Uppsala Universitet in Sweden. He noted that even modest bedroom lighting around one hundred lux has been shown to reduce deep sleep, raise heart rate, and impair insulin sensitivity.
Other long‑term studies have also linked typical indoor light levels to increased cardiovascular risk, including a higher likelihood of myocardial infarction.
Why darkness is so important for heart health
We often think of blue light from phones as the enemy of restful sleep, but ambient room light plays a bigger role than you might think.
A 2022 meta‑analysis found that people exposed to higher levels of artificial light at night had a 22 percent greater risk of sleep problems. Earlier research in older adults also found a link between nighttime light and atherosclerosis, which is the thickening of artery walls.
Cardiologist Jayne Morgan, MD, explains why light has such a powerful effect. “Inflammation is a result of stress, and inflammation is a primary driver of atherosclerosis and therefore heart disease and stroke,” she says. Because the heart and brain are so interconnected, what affects arterial health in one part of the body affects the other.
Light exposure disrupts the natural nighttime drop in blood pressure and delays the rise of morning hormones like cortisol. “Darkness signals the body to produce melatonin,” Morgan explains. Without that signal, the body’s recovery systems stay out of sync.
Sleep duration matters too. Morgan notes that “less than six hours of sleep has demonstrated a higher risk of heart disease.”
Tips for creating a truly dark sleep environment
If you’re ready to make your bedroom a healthier, darker sleep space, here are some simple changes that go a long way:
Cover your windows
Close curtains or shades tightly, and if they let in streetlight, consider blackout curtains. Aluminum foil over windows can work as a budget alternative.
Block door light
Even a small gap under the bedroom door can leak light. Turn off hallway lights or place a rolled towel at the base of the door.
Try a sleep mask
A well‑fitting eye mask can block out light completely and help your body slip into deeper sleep.
Switch to motion‑sensing nightlights
Instead of leaving lights on all night, use motion‑activated options that only turn on when necessary.
The bottom line
The science is increasingly clear: darker nights make for healthier days. Minimizing artificial light in your sleep environment supports deeper rest, calmer cardiovascular activity, and better long‑term heart health.
