Brighter Nights, Higher Heart Disease Risk: Study links Light Exposure to Cardiovascular Problems
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A groundbreaking new study reveals that exposure to bright light at night is associated with a considerably increased risk of heart disease – up to 50% higher – while ample daytime light may offer a protective effect.
Published in JAMA Network Open in October 2025, the research underscores the critical role of healthy circadian rhythms in cardiovascular health and highlights artificial nighttime lighting as a perhaps modifiable risk factor.
Researchers analyzed data from nearly 89,000 participants in the UK Biobank, utilizing wrist-worn light sensors to objectively measure individual light exposure over a nine-and-a-half-year period. The findings demonstrate a clear, dose-dependent relationship between nighttime light and increased cardiovascular risk.
The Circadian Rhythm Connection
Healthy heart function is deeply intertwined with well-regulated circadian rhythms, which govern essential bodily functions, including sleep-wake cycles, hormone release, and metabolism. Disruptions to these rhythms, often caused by exposure to artificial light at night, can negatively impact cardiovascular health.
The study revealed that individuals over 40 exposed to bright lights at night faced a heightened risk of various heart conditions, including stroke and heart failure. Notably, the associations were more pronounced in women for heart failure and coronary artery disease, and in younger participants for heart failure and atrial fibrillation.There was no clear modification observed for myocardial infarction or stroke.
Specifically, participants with the brightest nighttime exposure exhibited significantly greater risks of coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke compared to those experiencing the darkest nights. An increase in night-light exposure by one standard deviation raised the risk of all five cardiovascular outcomes by approximately 5-8%.
Interestingly, while daytime light exposure was initially linked to lower risks, these associations were not statistically meaningful after accounting for lifestyle factors. However, when physical activity was removed from the analysis, inverse associations re-emerged for heart failure and stroke, suggesting a complex interplay between light exposure and lifestyle.
Limitations and Future Research
While the study’s large sample size, objective light measurements, and extended follow-up period represent significant strengths, researchers acknowledge certain limitations. The study population was primarily of White ethnicity, limiting the generalizability of the findings. Additionally, the lack of information on specific light sources – such as screen time versus outdoor lighting – and the inability to definitively prove causality are areas for future investigation.
Researchers also noted that sleep duration and efficiency were objectively measured and included in their analyses,with short sleep partially mitigating some of the observed associations.
Implications for public Health
These findings underscore the importance of minimizing exposure to artificial light at night and maximizing exposure to natural daylight. Maintaining dark nights and prioritizing adequate daylight exposure should be integral components of urban health strategies.
“This research highlights artificial nighttime lighting as a potentially modifiable environmental risk factor for cardiovascular disease,” a senior official stated. “It reinforces the need for public health initiatives focused on promoting healthy sleep habits and optimizing light environments.”
Further research is needed to fully elucidate the underlying mechanisms linking light exposure to cardiovascular disease, including the role of melatonin secretion, which was not directly examined in this study. Though,the current evidence strongly suggests that a conscious effort to regulate our exposure to light could significantly benefit heart health.
Journal reference: windred, D.P., burns, A.C., Rutter, M.K., Lane, J.M., Saxena, R., Scheer, F.A.J.L., Cain, S.W., Phillips, A.J.K. (2025). Light exposure at night and cardiovascular disease incidence. JAMA Network Open 8(10): e2539031. DOI: 10.1001/jamanetworkopen.2025.39031. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2840489
