A New Concern for Heart Health
A new study published in the European Heart Journal has found that greater exposure to light during nighttime is associated with potentially harmful changes in heart structure and function.
Researchers found that people exposed to higher levels of nighttime light had signs of cardiac remodelling, including changes in the size and thickness of heart chambers and subtle reductions in cardiac function. The findings add to growing evidence that the modern habit of sleeping around artificial light may have consequences beyond sleep quality.
How Was the Study Conducted?
The researchers analysed data from more than 11,000 participants from the UK Biobank. Participants wore a wrist device containing a light sensor for seven days, allowing researchers to objectively measure their exposure to light during nighttime.
Around three years later, participants underwent cardiovascular magnetic resonance imaging, or CMR, to assess the structure and function of their hearts.
The researchers also examined longer term cardiovascular outcomes in a much larger group of more than 73,000 participants.
Even Low Levels of Light Were Examined
The study compared people with essentially no nighttime light exposure with those experiencing more than 3 lux of light.
For context, 3 lux is a relatively low level of illumination. It can be comparable to a dim hallway light entering through a partially open door or a phone screen operating at low brightness near the bed.
This is important because the study was not simply examining people sleeping under bright room lights. It looked at relatively subtle nighttime exposure as well.
Changes in the Left Side of the Heart
One of the major findings involved the left ventricle, the heart chamber responsible for pumping oxygen rich blood throughout the body.
People with higher nighttime light exposure had greater left ventricular mass and thicker heart walls. The study found a 2.4 percent greater indexed left ventricular mass and a 1.5 percent greater mean wall thickness compared with people without nighttime light exposure above 3 lux.
Researchers also observed a 1.9 percent lower myocardial contraction fraction, suggesting subtle changes in the heart’s ability to contract.
Other Heart Chambers Were Also Affected
The associations were not limited to the left ventricle.
Higher nighttime light exposure was also associated with changes involving the right ventricle and left atrium. Researchers observed larger right ventricular volumes and a larger left atrial volume, along with reduced left atrial ejection fraction.
The study also identified reduced myocardial deformation, another indicator of subtle changes in cardiac function that may occur before obvious clinical symptoms develop.
A Possible Link With Future Cardiovascular Disease
The researchers did not stop at imaging findings. They also followed participants for several years to examine cardiovascular outcomes.
Compared with people who had no nighttime light exposure above 3 lux, those with higher exposure had:
• 29 percent higher risk of heart failure
• 15 percent higher risk of atrial fibrillation
• 24 percent higher risk of myocardial infarction
• 33 percent higher risk of stroke
• 26 percent higher risk of cardiovascular disease mortality
These findings show an association and do not by themselves prove that nighttime light directly causes these cardiovascular conditions.
Sleep May Play an Important Role
One possible explanation involves sleep.
The researchers found that shorter sleep duration partly explained the relationship between nighttime light exposure and several adverse cardiac changes. Depending on the specific cardiac measurement, shorter sleep appeared to account for roughly 24 to 49 percent of the observed associations.
Nighttime light can interfere with the body’s circadian system, which helps regulate sleep, hormones, blood pressure and other cardiovascular processes.
This suggests that the problem may not simply be the light itself, but the biological disruption that nighttime light can create.
Why Light at Night Matters in Modern Life
Artificial light has become a normal part of modern living.
Streetlights, bedroom lighting, television screens, smartphones, charging indicators and other electronic devices can create continuous low level illumination after sunset.
Unlike many cardiovascular risk factors, nighttime light exposure is potentially modifiable. People can reduce unnecessary light in their sleeping environment without medication or complex interventions.
Simple Ways to Create a Darker Sleep Environment
The researchers suggest that reducing nighttime light could become one practical component of cardiovascular health strategies.
Simple measures include keeping unnecessary lights switched off, using curtains to block outdoor light, moving bright electronic devices away from the bed and using an eye mask when appropriate.
The broader goal is simple: create a darker environment during sleep while maintaining adequate and consistent sleep duration.
What This Study Does Not Prove
The findings should be interpreted carefully.
This was an observational study, meaning researchers identified associations between nighttime light exposure, cardiac changes and cardiovascular outcomes. It cannot establish that nighttime light directly caused the observed heart changes.
The study population was also predominantly White and generally healthier than the broader population, which may limit how widely the findings can be applied.
Further research will be needed to determine whether actively reducing nighttime light exposure can prevent or reverse cardiovascular changes.
A Small Lifestyle Factor With Potentially Large Implications
Heart health is influenced by many interconnected factors, including blood pressure, diabetes, smoking, physical activity, diet, stress and sleep.
Nighttime light may represent another environmental factor that deserves greater attention.
The new findings are particularly interesting because researchers were able to connect objectively measured nighttime light exposure with detailed cardiac imaging and longer term cardiovascular outcomes.
