Overview
- A study published Sept. 9 in the European Heart Journal analyzed 11,071 UK Biobank participants who wore wrist light sensors for seven days and received cardiac MRI scans about three years later.
- Participants with nighttime exposure above roughly 3 lux showed small but consistent changes: about 2.4% greater left ventricular mass, 1.5% thicker heart walls, and a 1.9% lower myocardial contraction fraction, with clear dose–response patterns.
- Mediation analysis attributed roughly 24%–49% of the association to shorter sleep caused by night light, and authors cite likely roles for circadian disruption, melatonin suppression, blood pressure shifts, and inflammation for the remainder.
- The study cannot prove cause because it is observational and limited by a one-week wrist-measured exposure window, no measurement of light spectrum or eye exposure, and a predominantly White UK sample.
- Editors and the study team recommend low-cost steps such as blackout curtains, dim warm bedside lighting, covering LEDs and shielded or dimmable streetlights while urging replication, longer and spectral exposure studies, diverse cohorts, and interventional trials.