Let’s say you’ve got stellar nighttime habits: You put away your phone, keep consistent sleep and wake times and get 8 hours of shut-eye every single night.
You might think you’ve got your routine down pat. But there’s another factor that could be quietly affecting your health — and it’s probably in your bedroom right now.
A new study suggests that a seemingly harmless nighttime habit could alter the structure and function of your heart, potentially increasing your risk of serious cardiovascular problems.
The perpetrator? Light exposure, even the smallest amount.
Researchers found that sleeping in a room with 3 lux of light or more was associated with changes in your heart muscle compared with those sleeping in near darkness.
We’re not just talking about leaving your lamp on on or staring at the glow of your screen in bed. Even dim light could make a difference.
For context, 3 lux is roughly equivalent to moonlight or light bleeding under a closed bedroom door, according to CNN. A streetlight might produce around 15 lux, an office 500 lux and an overcast day 1,000 to 5,000 lux.
In a world where lights are on 24/7, is it really possible to avoid nighttime light exposure?
Experts say yes — and the fix is easier than you might think.
How dim lights affect the heart
Researchers compared people who slept with 3 or more lux of light in their rooms with people who slept in near darkness.
They found that people exposed to more light had thicker walls in the left ventricle, the heart’s main pumping chamber. This thickening can reduce the chamber’s capacity to fill and pump blood effectively.
The condition, called left ventricular hypertrophy, can lead to serious conditions, including heart failure, irregular heart rhythms (arrhythmias), reduced blood flow to the heart (ischemic heart disease) and cardiac arrest.
The researchers also found that the heart did not contract or pump as effectively in people exposed to more light. Together, these findings suggest that nighttime light exposure may contribute to changes in the heart that increase risk of cardiovascular disease.
These changes are “typically [seen] in response to chronic stress or injury to the heart,” said author Lu Qi, of Tulane University. “It’s our body’s way of adapting to that stress, but ultimately it weakens the heart and can lead to heart failure.”
“It is time for clinicians, particularly those managing patients with heart failure or atrial fibrillation, to start asking about the sleep environment: how dark the bedroom is, whether the patient works night shifts, and how much screen use occurs after sunset,” said Thomas Münzel from University Medical Center Mainz, Germany.
How to stay in the dark
Münzel recommends “simple and inexpensive fixes.”
These include blackout curtains, choosing warm-colored bedside lighting and covering the small standby LEDs on household electronics. Several manufacturers even sell stickers designed to dim or block the tiny lights that remain on household devices.
And if you can’t completely darken your room, a sleep mask might be worth trying.
The researchers didn’t study exactly how nighttime light affects the heart, but they offered one possible explanation: Light may disrupt the circadian rhythm, the body’s natural sleep-wake cycle associated with the morning light. (Yes, our eyelids block out light, but light still can and does pass through.)
“From a public health perspective, the implications are larger still,” Münzel said.
“Light pollution is one of the few environmental hazards that cities can control directly and affordably. Shielded fixtures, warm-spectrum bulbs, and dimming or motion-activated streetlights are already available, energy-efficient, and climate-friendly.”
