What's new?

This is the first study in Poland to evaluate the association between light pollution (LP) and hospitalizations for cardiovascular diseases (CVDs) in the context of the external exposome. The study analyzed over 2 million hospitalizations within 9 years across 101 counties in eastern Poland, incorporating socioeconomic status and air pollution exposure. The effects of LP exposure vary depending on specific CVD, and are most pronounced in the case of ischemic stroke and atrial fibrillation. These findings underscore the harmful effects of nontraditional environmental risk factors on cardiovascular health, offering new insights into the broader implications of exposure to LP.

Introduction

Cardiovascular diseases (CVDs) remain a significant public health and socioeconomic challenge. Despite substantial progress in both the prevention and treatment methods, CVDs continue to be the leading cause of mortality globally.¹ Furthermore, the economic burden associated with comprehensive care for patients with CVD is immense, with scientific studies estimating it at 282 billion EUR annually for the population of the European Union.² For many years, efforts have been directed toward reducing the prevalence of well‑established, classic, and modifiable populational cardiovascular risk factors, such as smoking, hypertension, excessive body mass index (BMI), and lack of physical activity. However, in recent years, increasing attention has been given to the threats arising from the exposome, defined as the cumulative adverse impact of all environmental hazards to which an individual is exposed from birth to death.³

One component of the exposome is air pollution (AP), whose harmful effects on CVD occurrence are relatively well documented.^4-7 AP is associated with a higher number of attributable deaths than risk factors such as elevated low‑density lipoprotein cholesterol levels, kidney dysfunction, or high BMI.⁸ In recent years, the influence of other nonclassical cardiovascular risk factors has been increasingly recognized—one of which is light pollution (LP). This environmental risk factor is defined as an alteration in night sky brightness caused by anthropogenic light emissions.⁹ The prevalence of this pollutant was demonstrated by Falchi et al,⁹ showing that 83% of the global population and 99% of the populations in Europe and the United States live under light‑polluted night sky.

The association between exposure to LP and the prevalence and mortality caused by CVDs is a relatively new area of research. However, findings from recent publications, including a study by Sun et al,¹⁰ demonstrate a growing importance of this issue, given that increased LP intensity was associated with a higher risk of both hospitalization and death due to coronary artery disease (CAD). These results underscore the need for further comprehensive investigations into the impact of this nonclassical risk factor on human health.

Equally important is understanding the mechanisms through which exposure to nontraditional cardiovascular risk factors, such as LP, contributes to increased CVD risk. One widely discussed mechanism linking LP to adverse cardiovascular outcomes is a disruption of the circadian rhythm. LP can alter sleep architecture by reducing melatonin secretion and modifying the duration of sleep stages.¹¹ Sleep disturbances negatively impact the expression and function of circadian‑regulated genes, leading to endothelial dysfunction, impaired coagulation regulation, dysregulated blood pressure and heart rate—all of which are pathways to CVD development.¹² Another significant consequence of the circadian rhythm disruption is its impact on mental health, which is increasingly recognized as an indirect but potent contributor to CVD risk,^13,14 underscoring the multifaceted effects of circadian dysregulation. Despite growing evidence, further research is urgently needed to elucidate the precise mechanisms by which the exposome, including LP, affects human health. Such studies could pave the way for targeted interventions and improved preventive strategies.

Given the significant public health, economic, and social burden of CVDs, as well as the pressing need to identify and evaluate new, nonclassical harmful risk factors, our study assessed the relationship between LP intensity and the odds of hospitalizations for newly‑diagnosed ischemic stroke (IS), atrial fibrillation (AF), and myocardial infarction (MI), categorized as ST‑segment elevation MI (STEMI) and non‑STEMI (NSTEMI). The critical importance of these CVDs is underscored by the number of deaths they cause; for example, in 2021, they accounted for over 13.5 million deaths worldwide.¹ Our analysis, which covered 101 counties in eastern Poland and accounted for socioeconomic status (SES) and other exposome components, such as AP, addresses a significant gap in the current understanding of harmful effects of LP. The findings emphasize the need for further research on this emerging environmental risk factor.

Patients and methods

Study design

This study employed a longitudinal model covering the years 2012–2020 in eastern Poland to assess the impact of chronic exposure to LP on cardiovascular health outcomes. Exposure variables were derived from the National Aeronautics and Space Administration (NASA) and other organizations’ satellite system and were aggregated at the annual level for all counties included in the analysis. Based on available satellite data, including night‑time light intensity, a selection process was conducted to identify the indicator that best represents the actual burden of LP. Following a literature review, minimization of data gaps, and the need for standardization independent of latitude and altitude, the area‑weighted night‑light radiance (nW/cm²/sr) was chosen for the final analysis. This metric accounts for both the light intensity detected by satellites and the geographic area of a given region, allowing for a more precise assessment of actual LP levels. The use of this indicator enables a more realistic evaluation of exposure than conventional metrics based solely on raw radiance values. By weighting for surface area, the index does not favor highly urbanized regions, where naturally higher light emissions occur, thus eliminating potential biases resulting from data aggregation. This approach prevents artifacts where higher light levels would merely reflect a larger population size and more intensive urban infrastructure development. A key element of the analysis was the use of individual‑level patient data, which were subsequently aggregated at the county level. This method prevented errors related to the aggregation of disease cases in urban environments, which could lead to misleading conclusions suggesting an association driven solely by higher concentrations of health care facilities and urban populations. Dependent variables included hospitalization rates for CVDs, based on over 2 million individual cases, obtained from the Polish National Health Fund. Due to the nature of the data, differences in reporting across regions, and inconsistencies in diagnosis coding, the final analysis focused on acute hospital admissions for NSTEMI, STEMI, AF, and IS. To ensure comparability between regions, standardized hospitalization rates (SHRs) were calculated for each county, effectively eliminating variations due to demographic differences and urbanization levels. Standardization was conducted with reference to the population of 27 countries of the European Union. To account for potential confounding factors, the analysis incorporated data on AP, SES, and meteorological conditions. AP exposure was determined based on the concentrations of particulate matter with diameter below 2.5 µg (PM_2.5), nitrogen dioxide (NO₂), carbon oxide (CO), and ozone (O₃), while SES was assessed using gross domestic product (GDP) per capita. Meteorological conditions, including temperature, humidity, and atmospheric pressure, were also considered. All variables were aggregated at the annual level for each county, facilitating the assessment of long‑term effects of LP exposure on the population health. The study design is presented in Figure 1.

Results

During the study period, data on over 2 million individual hospitalizations were obtained, including 55 081 emergency admissions due to STEMI, 69 112 due to NSTEMI, 228 410 cases of AF, and 131 085 cases of IS. The majority of NSTEMI cases involved men (60.9%) at a mean (SD) age of 70.2 (11.9) years. Similarly, STEMI hospitalizations predominantly affected men (64.6%) at a mean (SD) age of 67.5 (12.5) years. Conversely, the majority of hospitalizations for AF (52.7%) and IS (51.6%) involved women. The mean (SD) age was 73.9 (12.2) years for the IS patients, and 69.6 (11.2) years for the individuals with AF.

Median (IQR) SHR per 100 000 population was calculated for each condition and amounted to 80.83 (66.2–99.12) for STEMI, 107.62 (79.85–131.81) for NSTEMI, 279.92 (183.51–468.5) for AF, and 207.18 (172.16–244.71) for IS. Detailed baseline characteristics of the analyzed population and SHR values and trends are presented in Table 1 and in Supplementary material, Figure S1.

LP intensity was expressed in units of radiance (nW/cm²/sr). The median (IQR) value of area‑weighted radiance measurements was 2260.52 (1481.75–3961.17) nW/cm²/sr, the highest level of LP intensity reaching 23 548 nW/cm²/sr was observed in the Kielce county in 2012. Visualization of the average level of LP intensity for each county in the study period is provided in Supplementary material, Figure S2. The yearly averages of the assessed AP levels were higher than the World Health Organization threshold values.²⁶ According to the meteorological data, mean (SD) yearly temperature was 8.97 (0.81) °C, humidity was 78.46% (2.11%), and mean (SD) atmospheric pressure was 991.78 (6.23) hPa. Detailed information about LP, atmospheric conditions, and AP data are presented in Table 2 and Supplementary material, Figure S3.

In the unadjusted model, an increase in yearly LP intensity by 1 IQR was associated with 23% higher odds of hospitalizations for AF (OR, 1.23; 95% CI, 1.21–1.25; P <⁠0.001), a 10% increase for IS (OR, 1.1; 95% CI, 1.08–1.13; P <⁠0.001), and a 15% increase for STEMI (OR, 1.15; 95% CI, 1.11–1.19; P <⁠0.001). For NSTEMI, the 3% increase in odds (OR, 1.03; 95% CI, 0.99–1.06) was not significant.

Significant associations for AF and IS remained consistent across all adjusted models with confounding variables. In model 9, which included GDP, meteorological conditions, and concentrations of CO, NO₂, and PM_2.5 as confounding variables, and in model 10, which differed by including O₃ concentrations instead of CO, the ORs for AF were 1.16 (95% CI, 1.14–1.18; P <⁠0.001) and 1.15 (95% CI, 1.13–1.17; P <⁠0.001), respectively. For IS, the increase was 6% (OR, 1.06; 95% CI, 1.04–1.09; P <⁠0.001) and 7% (OR, 1.07; 95% CI, 1.05–1.1; P <⁠0.001), respectively.

For STEMI and NSTEMI, the adjusted models indicated higher but insignificant odds of hospitalization. Detailed results for each model are presented in Figure 2 and Supplementary material, Table S1.

Discussion

The principal finding of this study is that prolonged exposure to LP may be associated with higher odds of hospitalization associated with CVDs, especially IS and AF.

To our knowledge, it is the first research of this kind in Poland, and the first in the world to assess the relationship between this environmental risk factor and AF, the most common arrhythmia²⁷ in the general population and a significant public health issue, strongly connected with exposome, especially with AP.²⁸ The impact of LP on human health has been a subject of interest for several decades,²⁹ but its effects on the cardiovascular system have only recently gained significant attention. This study contributes to filling the gap in current evidence emphasizing the need for precise regulatory standards and targeted strategies to mitigate exposure to environmental risk factors such as LP. Moreover, they highlight the importance of developing more advanced and accurate methodologies to assess CVD risk within the entire exposome, ultimately enhancing preventive strategies for cardiovascular health.

The occurrence of AF may be linked to the dysregulation of clock‑controlled genes,³⁰ whose function is disrupted by LP, leading to circadian rhythm disturbances. In the case of IS, a CVD with the second highest death toll¹ and projected increasing incidence in the coming years,³¹ our findings align with those published by Yonghao et al³¹ showing that a 1‑IQR increase in LP intensity was associated with a 14% higher risk of IS (hazards ratio [HR], 1.14; 95% CI, 1–1.3). The rising prevalence of IS may be partly explained by the increased risk of AF among individuals exposed to LP, as AF accounts for approximately 25% of IS cases.³²

Another potential pathophysiological mechanism linking LP exposure to a higher IS risk is its association with carotid atherosclerosis. For example, Obayashi et al³³ demonstrated that greater LP exposure correlated with increased intima‑media thickness, further supporting the role of this nonclassical risk factor in IS development. The findings of this study align with the holistic or integrated care management of AF recommended in global guidelines that emphasize going beyond anticoagulation alone.^34-36 Similar integrated care approach has been proposed for stroke management.^37,38

Managing exposure to LP is an integral part of risk factor and comorbidity management (as well as lifestyle factors), and may contribute to a reduction in stroke incidence among AF patients. Additionally, by lowering the number of acute AF episodes, it plays a role in symptom management. Routine assessment of LP exposure is also a key component of regular review and evaluation, reinforcing its relevance within the comprehensive integrated care framework for AF management.³⁹

Regarding CAD risks, Sun et al¹⁰ demonstrated in 2021 that in an elderly population in Hong Kong, a 1‑IQR increase in the exposure to LP was associated with a HR increase for CAD‑related hospitalizations and deaths (HR, 1.11; 95% CI, 1.03–1.18 and HR, 1.1; 95% CI, 1–1.22, respectively) in fully adjusted models accounting for other exposome components, such as PM_2.5 concentrations and noise intensity. Difference in the results of this research regarding STEMI and NSTEMI could be attributed to considerable harmful effects of specific APs included in these models. This observation aligns with the unique characteristics of AP in the analyzed regions. Unlike classical smog types, such as the London smog, prevalent in highly‑urbanized areas and marked by high concentrations of SO₂, PM_2.5, and CO, or photochemical smog, also known as Los Angeles type smog,^40,41 the so‑called Polish smog, occurring in less‑urbanized areas of eastern Poland forms under specific atmospheric conditions, features relatively low concentrations of SO₂ and CO but elevated levels of PM_2.5. As demonstrated in our previous research, this distinct composition of APs is particularly detrimental in the context of acute coronary syndrome risk.⁴ These findings underline the necessity of considering regional pollution patterns and their interaction with LP in studies addressing cardiovascular risks.

An important issue in public health is the need to implement methods that enable a more individualized approach to CVD prevention. Currently, widely used tools for assessing the cardiovascular risk, such as the Systemic Coronary Risk Estimation 2 (SCORE2) and SCORE2‑Older Persons⁴² scales, do not account for nonclassical risk factors for CVD development. Incorporating exposure to AP into risk assessment models demonstrates strong predictive value for major cardiovascular events.⁴³ Therefore, it is essential to expand the existing risk stratification models by integrating the entire exposome, including exposure to LP, to facilitate a more holistic approach. Although there are currently no widely available methods that allow clinicians to assess the impact of LP on human health, we consider that informing patients may contribute to raising public awareness on this important issue.

One of the more significant challenges ahead is the need to establish thresholds for harmful LP levels and revise urban development policies in areas where the issue is most pronounced. Some countries, such as the Czech Republic, France, and Germany, have implemented policies aimed at reducing LP.^28,44 However, we believe it is essential to adopt universally accepted standards at a global level and initiate comprehensive efforts to achieve these goals. Such measures would improve health and well‑being of residents and ecosystems, as LP also negatively impacts numerous animal species.⁴⁵