Overview
- Researchers used wrist-worn light sensors worn for about a week and cardiac MRI roughly three years later in more than 11,000 UK Biobank participants to test links between light at night and heart structure.
- Those with the brightest bedrooms (around 3 lux) showed modest cardiac remodelling, including about 2.4% greater left-ventricle muscle mass, 1.5% thicker LV wall, and 1.9% lower myocardial contraction fraction.
- In a larger follow-up of roughly 73,000 people tracked for up to a decade, higher night light exposure was associated with higher adjusted risks of heart failure, myocardial infarction, stroke, and related cardiovascular outcomes.
- Shorter sleep explained roughly 25%–50% of the associations, and authors suggest additional mechanisms such as circadian disruption, autonomic changes, inflammation, and vascular effects.
- The study is observational with limits — one-week light sampling, no spectral or eye-exposure data, and a mostly White, healthier cohort — so authors and societies recommend replication, longer and spectral measurements, intervention trials, and simple measures to reduce bedroom light such as blackout curtains, dim warm lights, and covering glowing electronics.