Key takeaways
- Nighttime light exposure was associated with measurable changes in cardiac structure.
- Higher exposure was associated with reduced myocardial contraction and cardiac strain.
- Higher nighttime light exposure was associated with increased cardiovascular event risks.
- Shorter sleep statistically mediated some associations with cardiac measurements.
Darkness is part of the body’s nighttime rhythm, but artificial light can keep our surroundings bright long after the day has ended. Streetlights, indoor lighting, and other sources can make the biological night less dark than the body expects. That raises a simple but intriguing question: if the environment stays bright when the body is meant to be in its nighttime state, could the heart reflect that mismatch?
A new UK Biobank study explored this question by measuring nighttime light exposure with wrist-worn sensors and examining the heart with cardiac magnetic resonance imaging. Researchers found measurable differences in heart structure and function among people exposed to more light at night, along with associations with several cardiovascular outcomes. The findings provide a closer look at the relationship between nighttime light exposure and the heart, but the observational study cannot establish that the exposure caused these changes.
What does nighttime light exposure do to the heart?
A study published in the European Heart Journal found that higher nighttime light exposure was associated with several differences in cardiac structure and function. Researchers used light measurements from wrist-worn sensors and cardiac magnetic resonance imaging, or cardiac MRI, to examine the relationship. The study included more than 11,000 UK Biobank participants with suitable cardiac MRI data. Participants wore a wrist device containing a light sensor for seven days. Researchers defined each person’s biological night using the participant’s least active five-hour period and measured exposure above 3 lux.
The cardiac MRI results showed differences in several measurements among participants with higher nighttime light exposure. Compared with participants without exposure above 3 lux, the high-exposure group had a 2.4% greater left ventricular mass and a 1.5% greater mean wall thickness. The left ventricle is the chamber that pumps oxygen-rich blood through the body. Greater ventricular mass and wall thickness indicate differences in cardiac structure. The study does not establish that nighttime light exposure caused these differences.
The researchers also measured myocardial contraction fraction and cardiac strain. Myocardial contraction fraction was 1.9% lower in the high-exposure group. Global circumferential strain, global radial strain, and global longitudinal strain were also lower. Cardiac strain measures how the heart muscle changes shape during contraction. The findings indicate differences in cardiac function, but they do not show that participants had heart failure or another diagnosed cardiac condition.
Is light at night linked to cardiovascular disease?
The study also examined cardiovascular events during long-term follow-up. Depending on the outcome being studied, participants were followed for between 7.9 and 9.5 years. During follow-up, researchers recorded 1,391 myocardial infarctions, 996 strokes, 1,570 cases of heart failure, 3,195 cases of atrial fibrillation, and 884 cardiovascular deaths.
After adjustment for demographic, lifestyle, health, and environmental factors, higher nighttime light exposure was associated with higher risks of several cardiovascular outcomes. Compared with participants without exposure above 3 lux, the high-exposure group had a 24% higher risk of myocardial infarction, 33% higher risk of stroke, 29% higher risk of heart failure, 15% higher risk of atrial fibrillation, and 26% higher cardiovascular mortality.
These results are consistent with findings from an earlier JAMA Network Open study. That study followed 88,905 UK Biobank participants and found associations between brighter nighttime environments and coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke.
The two studies examined different outcomes. The earlier study focused on cardiovascular disease incidence, while the newer study combined cardiovascular outcomes with cardiac MRI measurements. The newer findings therefore provide information about cardiac structure and function as well as disease outcomes.
Does nighttime light cause heart problems?
The study does not show that nighttime light exposure causes changes in the heart or cardiovascular disease. It was an observational study, so participants were not assigned to different levels of nighttime light. Researchers adjusted for several potential confounding factors relevant to cardiovascular risk, and sensitivity analyses supported the main cardiac MRI findings. However, the study has limitations that affect how the results should be interpreted.
Light exposure was measured for only seven days. That period may not represent a person’s usual exposure over several years. The wrist sensors also did not measure the spectral composition of light, so the study could not determine whether specific wavelengths were associated more strongly with the cardiac findings. Shorter sleep may account for part of the observed association. The researchers found that shorter sleep statistically mediated some of the relationships between nighttime light exposure and cardiac measurements. For the relevant cardiac phenotypes, the estimated proportion mediated by sleep ranged from 24% to 49%.
These mediation results do not establish that shorter sleep is the mechanism connecting nighttime light exposure with cardiac changes. They indicate that sleep duration accounted for part of the statistical relationship observed in the study. The available evidence therefore shows an association between higher nighttime light exposure and differences in cardiac structure, cardiac function, and cardiovascular outcomes. The observational design means the findings cannot establish causation. Further research is needed to determine whether changing nighttime light exposure produces measurable changes in cardiovascular health.
FAQs on Nighttime Light Exposure effects on Heart Structure
Q: What is the link between nighttime light exposure and heart health?
A: Higher nighttime light exposure was associated with differences in heart structure and function in a large UK Biobank study. The researchers found greater left ventricular mass and wall thickness, along with differences in several measures of cardiac function, among people with higher exposure.
Q: Can exposure to light at night increase the risk of heart disease?
A: The study found that higher exposure to light during the biological night was associated with increased risks of myocardial infarction, stroke, heart failure, atrial fibrillation, and cardiovascular death. However, the study was observational, so it cannot establish that nighttime light directly causes cardiovascular disease.
Q: How does light at night affect the left ventricle?
A: Participants with higher nighttime light exposure had a 2.4% greater left ventricular mass and a 1.5% greater mean wall thickness compared with participants without exposure above 3 lux. The same group also had differences in myocardial contraction fraction and cardiac strain measurements.
Q: Is nighttime light exposure associated with heart failure?
A: Yes. The study found a 29% higher risk of heart failure in the high-exposure group compared with participants without exposure above 3 lux after adjustment for several demographic, lifestyle, health, and environmental factors. This is an association, not evidence that nighttime light exposure directly causes heart failure.
Q: Does sleeping with artificial light affect cardiovascular health?
A: The study found that shorter sleep duration statistically accounted for part of the association between nighttime light exposure and several cardiac measurements. The researchers estimated that sleep mediated between 24% and 49% of some associations, but the findings do not establish that reduced sleep is the mechanism responsible.
Q: How is nighttime light exposure measured in cardiovascular studies?
A: The UK Biobank study measured exposure using a wrist-worn device containing a light sensor. Participants wore the device for seven days, and researchers assessed light exposure above 3 lux during each participant’s biological night. This provided an objective individual-level measurement, although seven days may not represent long-term exposure.
Q: Is light pollution at night linked to stroke and atrial fibrillation?
A: The study found associations between higher nighttime light exposure and both stroke and atrial fibrillation. The high-exposure group had a 33% higher risk of stroke and a 15% higher risk of atrial fibrillation compared with the group without exposure above 3 lux.
Q: How does nighttime light exposure compare with daytime light exposure?
A: The researchers found that nighttime exposure showed stronger associations with cardiac measurements and cardiovascular outcomes than daytime bright-light exposure. Daytime exposure above 1,000 lux was associated with only one cardiac MRI phenotype and was not associated with cardiovascular disease outcomes or cardiovascular mortality in the analysis.
Q: Does sleeping in a dark room prevent heart disease?
A: The available study does not establish that sleeping in a dark room prevents heart disease. It shows an association between greater nighttime light exposure and cardiovascular outcomes, while important limitations include the observational design and the seven-day exposure measurement period. Further intervention studies are needed to determine whether reducing nighttime light changes cardiovascular risk.
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References
- European Society of Cardiology. Too much light at night changes the shape and working of the heart. Press Releases. Published on 10 Sep, 2026. Available from: https://www.escardio.org/news/press/press-releases/too-much-light-at-night-changes-the-shape-and-working-of-the-heart/
- Dai J, Dai W, Heianza Y, Qi L. Nighttime light exposure and cardiac structure and function. European Heart Journal. 2026: ehag563. Doi: 10.1093/eurheartj/ehag563.
- Windred DP, Burns AC, Rutter MK, Lane JM, Saxena R, Scheer FA, Cain SW, Phillips AJ. Light exposure at night and cardiovascular disease incidence. JAMA network open. 2025 Oct 23;8(10):e2539031. Doi: 10.1001/jamanetworkopen.2025.39031.