TL;DR: New research suggests that exposure to light while you sleep may be associated with changes in heart structure and a higher risk of cardiovascular disease. While the study doesn’t prove that nighttime light causes heart problems, creating a darker bedroom is a simple step that may support better sleep and heart health.
Most of us have at least a little light in our bedrooms at night. But new research suggests that nighttime light exposure may be associated with changes in the heart, giving us another reason to think about how dark our bedrooms really are.
A study published in the European Heart Journal found a clear link between nighttime light exposure and structural changes in the heart, the kind of changes that show up before cardiovascular disease does. Below, we'll break down what the researchers found, why it matters, and what you can actually do about it tonight.
Researchers analyzed data from 11,071 participants in the UK Biobank. Participants wore a wrist sensor for seven days that measured their exposure to light throughout the day and night. About three years later, they underwent cardiac MRI scans so researchers could examine the structure and function of their hearts.
The study specifically looked at exposure to more than 3 lux of light at night. Lux is a measure of how much light reaches a surface. For context, a very dark outdoor night can measure less than 1 lux, while typical indoor lighting is much brighter.
Compared with people who experienced almost no nighttime light exposure, those exposed to more light showed several differences in their hearts.
They had thicker walls in the heart's left ventricle, less space within the chamber, and signs of reduced flexibility in the heart muscle. Researchers also observed changes in the right ventricle and left atrium, suggesting the association wasn't limited to just one area of the heart.
These changes are consistent with what's known as cardiac remodeling, when the heart gradually changes its size, shape, structure, or function in response to stress or increased workload.
Researchers also examined cardiovascular outcomes in a larger group of more than 73,000 people who were followed for approximately eight to 10 years.
Greater nighttime light exposure was associated with:
29% higher risk of heart failure
24% higher risk of heart attack
33% higher risk of stroke
26% higher cardiovascular mortality
Now, important caveat: this is an observational study, so we cannot say that nighttime light directly causes heart disease. Other factors may also contribute. People exposed to more light at night may have different work schedules, sleep habits, screen use, or socioeconomic circumstances, or they may live in areas with greater outdoor light pollution.
Light is one of the signals your body uses to regulate its circadian rhythm, the internal clock that helps determine when you feel awake and when you feel sleepy. At night, darkness helps tell your body that it's time to rest.
Researchers believe nighttime light exposure may disrupt sleep and circadian rhythms. That disruption doesn't stay contained to your sleep quality. It can affect blood pressure, increase inflammation, and interfere with how your body regulates the heart and blood vessels overnight. Over time, those small nightly disruptions add up.
Interestingly, shorter sleep duration appeared to account for part of the association between nighttime light exposure and the heart changes observed in the study. That means the connection may not simply be about light itself. Light could also interfere with the quality or amount of sleep we're getting, which can have its own effects on cardiovascular health.
Here's where it gets interesting: you don't need a floodlight in your room for this to matter. The study compared people exposed to more than 3 lux of light overnight with those exposed to almost none.
For reference, experts generally recommend keeping your bedroom at 1 lux or less for quality sleep. That’s dimmer than most people realize and means eliminating or minimizing noticeable light sources in the room.
Tonight, turn off the lights and look around your bedroom. Is light coming through the curtains? Is your phone lighting up with notifications? Are there glowing LEDs on chargers, televisions, clocks or other electronics?
A few simple changes can help reduce nighttime light:
Heart disease is still the leading cause of death in the U.S., and it's also one of the biggest drivers of healthcare costs for employers. Anything that helps employees catch risk factors early, or make small changes before those risk factors turn into a diagnosis, is worth paying attention to.
This is also a sleep story, and sleep quietly affects almost everything HR cares about: focus, mood, sick days, even how patient someone is in a meeting. An employee who isn't sleeping well because their bedroom is too bright isn't going to show up as their best self, and they may not even realize light is the culprit.
A few ways HR and wellness teams can act on this:
Darkness may seem like a small detail when it comes to heart health, but researchers are beginning to look at nighttime light exposure differently. One of the study’s authors even suggested that darkness could eventually be considered an important environmental health factor, alongside things like clean air and blood pressure.
The encouraging part is that reducing nighttime light doesn’t require a major lifestyle change. Closing the blinds, covering glowing electronics, silencing screen notifications or using a sleep mask are all simple ways to create a darker sleep environment.
Tonight, once the lights are off, take a quick look around your bedroom. Notice the light coming from outside, your phone, a clock or other electronics. A few small changes could create a better environment for sleep and, based on emerging research, may be worth considering for your heart health, too.