Nighttime light linked to subtle heart changes and higher heart‑disease risk

Most people have sat in a lit room late at night or slept with some light seeping through curtains. A new study finds that higher light exposure at night is associated with small but consistent changes in heart structure and function and with higher risks of several cardiovascular outcomes.

The study was led by Jin Dai, Wen Dai, Yoriko Heianza, and Lu Qi and published in the European Heart Journal on 09 September 2026. It used data from 11,071 UK Biobank participants who wore wrist accelerometers with light sensors for seven days between 2013 and 2015 and later underwent cardiovascular magnetic resonance imaging (CMR) a median of about three years after baseline.

How the study worked

Participants wore an Axivity AX3 accelerometer with an integrated light sensor on their dominant wrist for seven days under free-living conditions. Researchers defined each person’s circadian night using the least-active five hours (L5) and calculated nighttime light exposure as minutes above 3 lux, a level reported to suppress melatonin.

Cardiac structure and function were measured by CMR scans and processed with an automated deep learning pipeline. The team examined left ventricular (LV), right ventricular (RV), and atrial measures, including volumes, LV mass, wall thickness, ejection fraction, myocardial contraction fraction, and global strain indices. Models adjusted for demographic, lifestyle, health, and environmental factors and tested whether sleep duration mediated associations.

Main findings

Compared with participants with no nighttime light exposure >3 lux, those with high exposure had 2–3% greater LV mass indexed to height1.7 and about 1–2% greater mean wall thickness, along with about 2% lower myocardial contraction fraction.

Myocardial deformation was worse with higher exposure: absolute global LV circumferential strain was lower by 2.7%, radial by 2.9%, and longitudinal by 2.8%. The right ventricle showed modestly greater indexed end-diastolic and end-systolic volumes, and the left atrium had 2.3% greater maximum volume and 1.1% lower ejection fraction.

All associations followed linear dose–response patterns. Shorter sleep duration statistically mediated 24%–49% of the observed associations.

Clinical outcomes

In analyses of up to 73,286 participants for incident events, high (vs none) nighttime light exposure was associated with higher risks during about 8–10 years of follow-up: 29% higher risk of heart failure, 15% higher risk of atrial fibrillation, 24% higher risk of myocardial infarction, 33% higher risk of stroke, and 26% higher risk of cardiovascular mortality.

Limitations

The study reports associations, not proven causes. Sleep duration mediation analyses assume no unmeasured confounding. The CMR sample excluded participants with prior cardiovascular disease and those without CMR data, which affected sample size. Measurement relied on wrist sensors with a specific spectral sensitivity and device calibration.

Practical implications

The authors note that nighttime light exposure and sleep duration are linked to the cardiac measures observed. The report highlights the roles of dark nights and adequate sleep for cardiovascular health as relevant considerations.

What’s next

The researchers also examined daytime light exposure and its potential effects, and they used causal mediation analyses to assess mechanisms. Further follow-up and complementary studies would be needed to expand understanding of how light exposure timing and intensity relate to heart health.