When sleeping, keep it dark!
"Exposure to light at night raises cardiovascular disease risk by up to 50 percent over sleeping in the dark, new research shows. But scientists say the effect isn’t from lack of sleep, but from disruption of the body’s master biological clock, the circadian rhythm. ...
For those experiencing the brightest nights, the research showed increased risk of between 30 percent and 50 percent for heart attack, stroke, heart failure, atrial fibrillation, and coronary artery disease. ...
The data did include light intensity but unfortunately provided no information about sources, such as streetlights, cellphone screens, nightlights, and television. ..."
From the key points and abstract:
"Key Points
Question Is personal light exposure at night associated with cardiovascular disease incidence?
Findings In this cohort study of 88 905 adults aged older than 40 years, exposure to brighter light at night was associated with higher risks of coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke, independent of established cardiovascular risk factors.
Meaning These findings suggest that avoiding exposure to night light may lower risk of cardiovascular diseases.
Abstract
Importance Light at night causes circadian disruption, which is a known risk factor for adverse cardiovascular outcomes. However, it is not well understood of cardiovascular diseases.
Objective To assess whether day and night light exposure is associated with incidence of cardiovascular diseases, and whether associations of light with cardiovascular diseases differ according to genetic susceptibility, sex, and age.
Design, Setting, and Participants This prospective cohort study analyzed cardiovascular disease records across 9.5 years (June 2013 to November 2022) from UK Biobank participants who wore light sensors in a naturalistic setting. Data were analyzed from September 2024 to July 2025.
Exposure Approximately 13 million hours of light exposure data, tracked by wrist-worn light sensors (1 week each), categorized into the 0 to 50th, 51st to 70th, 71st to 90th, and 91st to 100th percentiles.
Main Outcomes and Measures
Incidence of coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke after light tracking were derived from UK National Health Service records. Risks of cardiovascular diseases were assessed using Cox proportional hazards models (3 primary models adjusted at 3 levels) and reported as hazard ratios (HRs).
Results
A total of 88 905 individuals were included (mean [SD] age, 62.4 [7.8] years; 50 577 female [56.9%]). Compared with individuals with dark nights (0-50th percentiles),
those with the brightest nights (91st-100th percentiles) had significantly higher risks of developing coronary artery disease (adjusted HR [aHR], 1.32; 95% CI, 1.18-1.46), myocardial infarction (aHR, 1.47; 95% CI, 1.26-1.71), heart failure (aHR, 1.56; 95% CI, 1.34-1.81), atrial fibrillation (aHR, 1.32; 95% CI, 1.18-1.46), and stroke (aHR, 1.28; 95% CI, 1.06-1.55).
These associations were robust after adjusting for established cardiovascular risk factors, including physical activity, smoking, alcohol, diet, sleep duration, socioeconomic status, and polygenic risk.
Larger-magnitude associations of night light with risks of heart failure (P for interaction = .006) and coronary artery disease (P for interaction = .02) were observed for females, and larger-magnitude associations of night light with risks of heart failure (P for interaction = .04) and atrial fibrillation (P for interaction = .02) were observed for younger individuals in this cohort.
Conclusions and Relevance
In this cohort study, night light exposure was a significant risk factor for developing cardiovascular diseases among adults older than 40 years. These findings suggest that, in addition to current preventive measures, avoiding light at night may be a useful strategy for reducing risks of cardiovascular diseases."
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