Nocturnal Light Exposure: A Novel, Modifiable Cardiovascular Risk Factor
Night light = new CV risk factor
Brightest nights (≥91st percentile) → +32–56 % risk of CAD, MI, HF, AFib & stroke (fully adjusted HR 1.28–1.56; all p<0.001)
Dose-response
act on >70th percentile 0–50th (dark) = reference 51–70th ↑10 % | 71–90th ↑20 % | 91–100th ↑32–56 %
Daytime light is SAFE
More daytime lux = neutral or slightly protective. Only light during sleep hours harms.
Target these 2 groups first:
- Women: 50–60 % larger effect on HF & AFib
- Age <65: stronger signal for HF & AFib (p-interaction 0.02–0.04)
7 nights is enough to risk-stratify
One week of wrist light sensor (UK Biobank protocol) predicts 9-year events. Add to annual health-check or research studies.
2-minute patient script
“Doctor’s orders: after 11 pm your bedroom must be <1 lux. Phone → Night Shift, TV off, blackout curtains or eye-mask. Red night-light only.”
Conclusion
Night light is a new, independent heart risk as strong as smoking or salt. Switch off after 11 pm and cut your risk by up to 56 %. One week of dark sleep = 9 years of stronger heart.
