Who’d ever think that modern-day light sources could actually harm yoru heart?
But then again, we didn’t exactly evolve on bright lighting, either; the sun doesn’t count.
Artificial light at night is everywhere, especially in cities. Streetlights, billboards, porch lights and glowing windows all add up after dark.
A preliminary study suggests that this constant nighttime brightness may do more than disrupt sleep.
It may also increase stress in the brain, inflame blood vessels and raise the risk of heart disease.
You’ve certainly heard of noise pollution — perhaps how it can lead to high blood pressure (which in turn can damage heart function).
But lighting pollution may be just as real.
How Light Pollution Could Stress the Body
Researchers describe artificial light at night, often called light pollution, as nearly unavoidable in modern life.
This study is one of the first to combine brain imaging with satellite data to explore how nighttime light might affect the heart.
According to the research team, environmental stressors like noise and air pollution are already known to raise heart disease risk.
Light pollution may work in a similar way by activating stress pathways in the body.
What the Brain Scans Revealed
The study included about 450 adults with no known heart disease or active cancer.
All participants underwent the same PET/CT scan, a routine imaging test used at Massachusetts General Hospital.
The CT scan showed detailed anatomy, while the PET scan measured metabolic activity.
Together, these scans allowed researchers to measure stress signals in the brain and inflammation in the arteries at the same time.
Higher Nighttime Light Linked to Higher Risk
People exposed to higher levels of artificial light at night showed more brain stress activity and greater blood vessel inflammation.
They also had a higher risk of major heart events over time.
Medical records were reviewed by cardiologists who had no information that could influence their assessments.
The study found that as nighttime light exposure increased, so did heart disease risk.
Every standard deviation increase in light exposure was linked to about a 35% higher risk of heart disease over five years and a 22% higher risk over 10 years.
These links remained even after accounting for traditional risk factors like noise pollution and socioeconomic status.
Who Appears Most Vulnerable
Heart risks were highest among people living in areas with added stressors.
These included neighborhoods with heavy traffic noise or lower income levels.
Over a ten year follow-up period, 17% of participants experienced major heart problems.
How Brain Stress Leads to Heart Problems
Researchers found a nearly linear relationship between nighttime light and heart disease risk.
Even small increases in light exposure were linked to higher brain and artery stress.
When the brain senses stress, it activates signals that can trigger immune responses.
Over time, this can inflame blood vessels, contribute to artery hardening, and raise the risk of heart attack or stroke.
Ways to Reduce Light Exposure
You can reduce indoor nighttime light by keeping bedrooms dark or dimmed.
You can also make an effort to avoid nighttime shopping trips or “runs” just for some snackfood.
If you have a dog, try to get all its walking in before dark, though that’s not always going to be easy, especially for those who work traditional hours.
Avoiding screens like TVs, phones and tablets before bed may also help.
Why Circadian Health Is Important
Excessive nighttime light can disrupt circadian rhythms, suppress melatonin (the “sleep hormone”) and delay sleep onset.
Even low levels of light pollution have been linked to higher cardiovascular risk.
An example of a low level might be that “night light” you keep on in your bedroom overnight during sleep.
Strengths and Limits of the Research
The study was observational, meaning, it can’t show cause and effect.
For instance, could it be that those who have lifestyle habits that can lead to heart disease are more likely to be out and about at night in a busy brightly lit city?
Another limitation was that all participants came from one hospital system.
Researchers say larger and more diverse studies are needed.
More on How the Study Was Done
Health records were reviewed for 466 adults with a median age of 55.
Participants were scanned between 2005 and 2008 and followed through 2018.
Satellite data were used to estimate nighttime brightness around each person’s home.
During follow-up, 79 participants experienced major heart events.
The findings were presented at the American Heart Association’s Scientific Sessions 2025.
