Nighttime light exposure and cardiac structure and function.

BACKGROUND AND AIMS: Nighttime light exposure has emerged as a potential risk factor for cardiovascular disease (CVD). However, its impact on cardiac structure and function remains unknown. METHODS: This population-based cohort study included 11 071 UK Biobank participants who wore a wrist-worn accelerometer with an integrated light sensor for 7 days between 2013 and 2015 (baseline) and had subsequent cardiovascular magnetic resonance (CMR) imaging 3 years later. Nighttime light exposure >3 lux was estimated, and its dose-response relationships with CMR phenotypes were examined using generalized linear regression models. Associations of nighttime light exposure with incident CVD outcomes and mortality were examined using Cox models (n = 73 286). RESULTS: After multivariable adjustment, high (vs none) nighttime light exposure >3 lux was associated with left ventricular (LV) concentric hypertrophy and subclinical functional decline, including 2.4% (95% confidence interval 1.6%, 3.1%) greater LV mass indexed to height1.7, 1.5% (1.0%, 2.0%) greater mean wall thickness, and 1.9% (1.1%, 2.7%) lower myocardial contraction fraction. Nighttime light exposure was also associated with impaired myocardial deformation, including lower absolute global LV circumferential [-2.7% (-3.7%, -1.7%)], radial [-2.9% (-3.9%, -1.8%)], and longitudinal strain [-2.8% (-3.9%, -1.7%)] indices. Adverse associations were also observed for the right ventricle, including 0.9% (0.1%, 1.8%) greater end-diastolic and 1.6% (0.5%, 2.8%) greater end-systolic volumes indexed, and for the left atrium, including 2.3% (0.7%, 3.9%) greater maximum volume indexed and 1.1% (0.3%, 1.9%) lower ejection fraction. All associations exhibited linear dose-response relationships, with most partly mediated by shorter sleep duration (proportion mediated: 24%-49%). During 8-10 years of follow-up, participants with high (vs none) nighttime light exposure had 29% (12%, 49%) higher risk of heart failure, 15% (4%, 27%) higher risk of atrial fibrillation, 24% (7%, 44%) higher risk of myocardial infarction, 33% (11%, 59%) higher risk of stroke, and 26% (5%, 52%) higher risk of CVD mortality. CONCLUSIONS: Greater nighttime light exposure was associated with adverse cardiac remodelling and subclinical functional decline across multiple chambers, statistically mediated by shorter sleep duration. These findings provide potential mechanistic insights into how nighttime light exposure may elevate CVD risk and highlight dark nights and adequate sleep for cardiovascular health.