Researchers have discovered that people exposed to brighter light at night face up to 50% higher risks of heart disease, while daytime light may protect the heart by reinforcing healthy circadian rhythms.
In their recent study published in JAMA Network Open, they explored whether being exposed to light at night is associated with a higher risk of developing heart disease, particularly for those of a specific age, sex, or genetic makeup.
Their findings indicate that people over 40 exposed to bright lights at night face higher risks of heart disease, including stroke and heart failure, reports News-Medical.net. Associations were larger in females for heart failure and coronary artery disease, and in younger participants for heart failure and atrial fibrillation, with no clear modification for myocardial infarction or stroke.
Background
Healthy cardiovascular function relies on well-regulated circadian rhythms, which in turn influence vascular function, glucose tolerance, hormone levels, blood pressure, and heart rate.
Disruption of these rhythms, through exposure to light or irregular sleep patterns, can elevate blood pressure and heart rate, increase inflammation, and reduce heart rate variability.
Animal studies show that prolonged circadian disruption can cause structural heart changes, such as hypertrophy and fibrosis. It worsens heart failure. Epidemiological evidence also links shift work, which disturbs these rhythms, to greater cardiovascular mortality, coronary heart disease, and heart failure.
Light exposure at night is a key source of circadian disruption and has been linked to higher rates of coronary artery disease and stroke, as well as conditions like obesity, diabetes, and hypertension, which are known cardiovascular risk factors. However, previous studies often relied on satellite-based measures of outdoor lighting or on small cohorts rather than on direct personal light-exposure data.
Using wrist-worn light sensors from about 89 000 UK Biobank participants, earlier research found that brighter nights were associated with higher cardiometabolic mortality and type 2 diabetes. Building on this, the present study examined whether individual day and night light exposures predict incident cardiovascular diseases over 9.5 years of follow-up.
Wrist-work sensors
The large-scale cohort study used data from UK Biobank participants who wore wrist-worn light sensors for one week between 2013 and 2016. Participants’ light exposure was recorded continuously, processed to remove invalid data, and averaged into 24-hour profiles.
Factor analysis identified two main exposure periods: daytime (7.30am-8.30pm) and night-time (12.30am-6am). Participants were categorised into light-exposure percentiles, with the 0-50th percentile representing the darkest nights.
Cardiovascular outcomes, including stroke, atrial fibrillation, heart failure, myocardial infarction, and coronary artery disease, were identified using hospital, primary-care, and death-registry records. Individuals with pre-existing cardiovascular disease (CVD) were excluded.
Cox proportional-hazards models assessed the relationship between light exposure and disease risk, adjusting sequentially for demographic factors (ethnicity, age and sex), socioeconomic variables (deprivation, education and income), and lifestyle factors (urbanicity, diet, alcohol, smoking and physical activity). Additional models were tested for potential interactions with genetic risk scores, age and sex.
Daytime better
The 88 905 UK Biobank participants had an average age of 62.4 years and 57% female, and the data were analysed over an average follow-up of 7.9 years. Participants were free of cardiovascular disease at baseline.
Night-time light exposure showed a clear, dose-dependent association with a higher risk of heart disease, while daytime light exposure was linked to lower risks in minimally and socioeconomically adjusted models, but these associations were not significant after full lifestyle adjustment. When physical activity was excluded from the full model, inverse associations re-emerged for heart failure and stroke.
Compared with those in the darkest-night environment, participants with the brightest night exposure had significantly greater risks of coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke after adjusting for lifestyle, demographic, and socioeconomic factors.
In contrast, an increase in night-light exposure by one standard deviation raised the risk of all five cardiovascular outcomes by about 5%-8%. The associations were consistent across models and remained robust after adjustments.
Sex and age showed selective modifying effects, with larger associations in females for heart failure and coronary artery disease, and in younger individuals for heart failure and atrial fibrillation, with no clear modification for myocardial infarction or stroke. Associations also remained after accounting for polygenic risk, suggesting gene–environment correlation is unlikely to explain the results.
Sleep disturbance
This large prospective study demonstrates strong associations of higher night-time light exposure with elevated cardiovascular risk, though causality cannot be inferred. The mechanisms underlying this association could include circadian disruption and sleep disturbance, leading to vascular and metabolic stress. Reduced melatonin secretion was not directly examined in this study.
In contrast, greater daytime light exposure may support cardiovascular health by reinforcing circadian rhythms.
Key strengths of this analysis include a large sample size, objective light measurements, and a long follow-up period. However, limitations include potential residual confounding, limited ethnic diversity (primarily white participants), lack of information on light sources, and the inability to infer causality.
Sleep duration and efficiency were objectively measured and included in sensitivity analyses; short sleep partially attenuated some associations. Source information was unavailable, limiting the ability to adjust for behaviours correlated with light exposure.
Overall, these findings highlight artificial night-time lighting as a potentially modifiable environmental risk factor for cardiovascular disease, underscoring the importance of maintaining dark nights and adequate daylight exposure in urban health strategies.
Study details:
Light exposure at night and cardiovascular disease incidence
Daniel Windred, Angus Burns, Martin Rutter et al.
Published in JAMA Network Open on 23 October 2025
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 analysed 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 analysed from September 2024 to July 2025.
Exposure
Approximately 13m hours of light exposure data, tracked by wrist-worn light sensors (one week each), categorised 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 (three primary models adjusted at three 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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