Night Light and Circadian Disruption: Impacts on Cardiovascular Health

Recent research conducted by the Flinders Health and Medical Research Institute, in collaboration with teams from the UK and U.S., has identified a significant link between exposure to brighter night-time light and an increased risk of developing multiple cardiovascular diseases. The study, titled "Personal night light exposure predicts incidence of cardiovascular diseases in >88,000 individuals," analyzed data from over 88,900 UK Biobank participants who wore wrist-based light sensors for a week between 2013 and 2016 across various regions in the UK.

Circadian rhythms, the body's internal clock, regulate vital fluctuations in blood pressure, heart rate, hormone secretion, glucose metabolism, and platelet activity. Disruption to these rhythms has been associated with adverse health outcomes such as myocardial fibrosis, hypertension, inflammation, and impaired autonomic function. Prior studies often relied on satellite data or small cohorts, leaving a gap in understanding individual exposure at a population level.

In this extensive cohort analysis, researchers evaluated whether daytime and nighttime light exposure could predict the incidence of key cardiovascular conditions, including coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke. The analysis considered various factors, adjusting for age, sex, ethnicity, socioeconomic status, lifestyle habits, sleep patterns, clinical risk factors, and genetic predisposition.

Findings revealed that increased night-time light exposure correlates with a dose-response increase in cardiovascular risk across all five outcomes. Participants in the highest exposure percentile (90-100th percentile) demonstrated a 23–32% higher hazard for coronary artery disease, 42–47% for myocardial infarction, 45–56% for heart failure, 28–32% for atrial fibrillation, and 28–30% for stroke, compared to those in the lowest exposure group (0–50th percentile). These associations persisted even after controlling for physical activity, smoking, alcohol intake, diet, sleep duration, and genetic risk.

Notably, the study observed that women exhibited stronger links between night light exposure and certain conditions like heart failure and coronary artery disease, while younger participants showed more pronounced associations with heart failure and atrial fibrillation. The authors suggest that circadian misalignment caused by artificial light may induce metabolic and vascular disturbances, increasing disease susceptibility. Possible mechanisms include impaired glucose regulation leading to endothelial dysfunction and atherosclerosis, light-driven hypercoagulability raising thromboembolic risks, and sustained blood pressure elevation damaging vessel walls. Additionally, conflicting signals to cardiac rhythm nodes may heighten arrhythmia vulnerability.

Based on these insights, limiting exposure to bright artificial light during typical sleep hours is recommended as a practical addition to current cardiovascular prevention strategies. The authors advocate for circadian-informed lighting standards in homes, hospitals, and city planning to mitigate these risks.

This research underscores the importance of maintaining natural light-dark cycles for cardiovascular health and highlights the potential benefits of sleep hygiene and environmental modifications to support circadian alignment.