Many people use bright lights late at night without thinking much about it. Some scroll through their phones in bed, fall asleep with the television on, or keep bright lights glowing in the house long after dark.
A major new study now suggests that these common habits may be more harmful than people realize. Researchers from Flinders University in Australia have found that exposure to bright light at night may greatly increase the risk of serious heart problems, including heart attacks, strokes, heart failure, and irregular heart rhythms.
The study was published in JAMA Network Open and is believed to be the first large study to show that nighttime light exposure is an independent risk factor for cardiovascular disease.
This means the increased risk remained even after researchers accounted for many other important health factors such as exercise, diet, smoking, sleep habits, alcohol use, and genetic risk.
The research involved almost 89,000 adults in the United Kingdom. Scientists tracked participants’ exposure to light using special wrist-worn sensors that recorded light levels continuously.
In total, researchers collected more than 13 million hours of light exposure data. Participants were then followed for up to 9.5 years so scientists could track who later developed heart disease.
The results surprised even the researchers. People who were exposed to the brightest levels of light during the night had a 56% higher risk of developing heart failure and a 47% higher risk of suffering a heart attack compared to those exposed to the least amount of light at night.
The researchers also found increased risks for stroke, coronary artery disease, and atrial fibrillation, a common heartbeat disorder that can lead to serious complications.
Dr. Daniel Windred, the lead author of the study and a researcher with Flinders University’s FHMRI Sleep Health group, explained that many people do not realize how important darkness is for the body. According to him, nighttime light exposure disrupts the body’s internal clock, known as the circadian rhythm.
The circadian rhythm is the body’s natural timing system. It helps control when people feel awake and when they feel sleepy. It also affects hormone levels, metabolism, blood pressure, heart function, and many other important biological processes.
Humans evolved to follow natural patterns of light and darkness, with bright light during the day and darkness at night. Artificial lighting and electronic screens can interfere with this natural system.
“When people stay awake under bright lights or spend hours looking at screens late at night, the brain may become confused and think it is still daytime,” Dr. Windred explained.
This confusion can disturb sleep and place extra stress on the body over time. Scientists believe this stress may contribute to inflammation, higher blood pressure, and other changes that increase the risk of heart disease.
One important finding from the study was that women and younger adults seemed to be especially sensitive to nighttime light exposure.
Professor Sean Cain, one of the senior researchers involved in the project, said women exposed to high levels of light at night had heart failure risks similar to men. This stood out because women usually have some natural protection against heart disease earlier in life.
The researchers also emphasized that this problem is not limited to people who work night shifts or live in brightly lit cities. Everyday habits may expose people to harmful amounts of light. Looking at a phone in bed, sleeping with a lamp or television on, or using bright overhead lighting late at night may all affect the body’s internal clock.
Earlier research into nighttime light mostly relied on satellite images or simple questionnaires.
This new study was different because it used wearable devices that measured real-time personal light exposure, including indoor lighting. This gave researchers a much more accurate picture of how much light people were actually exposed to during the night.
Heart disease remains the leading cause of death worldwide. Because of this, researchers believe people should start taking nighttime light exposure more seriously, just as they already think about smoking, unhealthy diets, and lack of exercise.
The good news is that reducing nighttime light exposure can be simple and inexpensive. Researchers suggest using blackout curtains, dimming lights in the evening, and turning off electronic screens at least one hour before bedtime. Using warmer and softer lighting at night may also help support the body’s natural sleep cycle.
The scientists behind the study are now calling for more research to better understand how light affects health and to help create healthier lighting guidelines for homes, hospitals, workplaces, and public spaces.
Professor Cain said protecting natural sleep rhythms could become an important new way to lower heart disease risk. As scientists continue to learn more about the connection between light, sleep, and heart health, the message is becoming increasingly clear: darkness at night may be just as important for health as sunlight during the day.
Researchers are also continuing to study other factors that affect heart health.
Recent studies have looked at blood thinners that may not prevent strokes in some patients with heartbeat disorders, diabetes drugs that may protect the hearts of older adults, the possible heart benefits linked to light-to-moderate alcohol consumption, and questions about the long-term use of certain blood pressure medications after heart attacks.
This growing area of research highlights how everyday lifestyle habits can quietly shape long-term health. Simple changes to nighttime routines may one day become part of standard advice for protecting the heart and improving overall wellbeing.
If you care about heart health, please read studies about how eating eggs can help reduce heart disease risk, and herbal supplements could harm your heart rhythm.
For more health information, please see recent studies about how drinking milk affects risks of heart disease and cancer, and results showing strawberries could help prevent Alzheimer’s disease.
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